diff --git a/toolchain/semantics/BUILD b/toolchain/semantics/BUILD
index f21dc058fbca..700bc87a5825 100644
--- a/toolchain/semantics/BUILD
+++ b/toolchain/semantics/BUILD
@@ -2,6 +2,7 @@
 # Exceptions. See /LICENSE for license information.
 # SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
+load("//bazel/fuzzing:rules.bzl", "cc_fuzz_test")
 load("//bazel/sh_run:rules.bzl", "glob_sh_run")
 load("//testing/file_test:rules.bzl", "file_test")
 
@@ -115,6 +116,17 @@ file_test(
     ],
 )
 
+cc_fuzz_test(
+    name = "semantics_fuzzer",
+    size = "small",
+    srcs = ["semantics_fuzzer.cpp"],
+    corpus = glob(["fuzzer_corpus/*"]),
+    deps = [
+        "//toolchain/driver",
+        "@llvm-project//llvm:Support",
+    ],
+)
+
 glob_sh_run(
     args = [
         "$(location //toolchain/driver:carbon)",
diff --git a/toolchain/semantics/fuzzer_corpus/005cacf2254cee9c357347503a715e3b680b7284 b/toolchain/semantics/fuzzer_corpus/005cacf2254cee9c357347503a715e3b680b7284
new file mode 100644
index 000000000000..17dad87b1779
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/005cacf2254cee9c357347503a715e3b680b7284
@@ -0,0 +1,19 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+fn CompareStr(s: String) -> i32 {
+  if (s == "str\n") {
+    return 0;
+  }
+  return 1;
+}
+
+fn Main() -> i32 {
+  return CompareStr("str\n");
+}
diff --git a/toolchain/semantics/fuzzer_corpus/010856053137c0432260e9145d6f171ae227c715 b/toolchain/semantics/fuzzer_corpus/010856053137c0432260e9145d6f171ae227c715
new file mode 100644
index 000000000000..2b53199da4f2
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/010856053137c0432260e9145d6f171ae227c715
@@ -0,0 +1,15 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  var t2: {.x: i32, .y: i32} = {.x = 2, .y = 5};
+  t2.y = 3;
+  // 3 - 2 - 1
+  return t2.y - t2.x - 1;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/0112278cfd21507f5266dfd89b7dc51a6ea801b3 b/toolchain/semantics/fuzzer_corpus/0112278cfd21507f5266dfd89b7dc51a6ea801b3
new file mode 100644
index 000000000000..483083daf9df
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/0112278cfd21507f5266dfd89b7dc51a6ea801b3
@@ -0,0 +1,14 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 1
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  returned var x: i32;
+  x = 1;
+  return var;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/01cd4d9d3357b42f67e7b85e3b971ade1ab4a3d5 b/toolchain/semantics/fuzzer_corpus/01cd4d9d3357b42f67e7b85e3b971ade1ab4a3d5
new file mode 100644
index 000000000000..aa1ffe4f7c45
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/01cd4d9d3357b42f67e7b85e3b971ade1ab4a3d5
@@ -0,0 +1,17 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 5
+
+package ExplorerTest api;
+
+class A {
+  var n: i32;
+  fn Get[self: Self]() -> i32 { return self.n; }
+}
+
+fn Main() -> i32 {
+  return ({.n = 5} as A).Get();
+}
diff --git a/toolchain/semantics/fuzzer_corpus/03a9b31a0b80b5c661d405b654a51932bf3dabad b/toolchain/semantics/fuzzer_corpus/03a9b31a0b80b5c661d405b654a51932bf3dabad
new file mode 100644
index 000000000000..9f46c83fdc5a
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/03a9b31a0b80b5c661d405b654a51932bf3dabad
@@ -0,0 +1,44 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+interface HasTypes {
+  let A:! type;
+  let B:! type;
+  let C:! type;
+  let D:! type;
+  let E:! type;
+  let F:! type;
+}
+
+interface HasParams(A:! type, B:! type, C:! type, D:! type) {
+  let V:! HasTypes;
+}
+
+// Here we discover that there is a rewrite for `HasParams(...).V` only after
+// substitution converts each one to `HasParam(X, X, X, X).V`.
+fn F[X:! (HasTypes & HasParams(.Self, .Self, .Self, .Self)) where
+       .Self impls HasParams(.A, .A, .A, .A) and
+       .Self impls HasParams(.B, .B, .B, .B) and
+       .Self impls HasParams(.C, .C, .C, .C) and
+       .Self impls HasParams(.D, .D, .D, .D) and
+       .Self impls HasParams(.E, .E, .E, .E) and
+       .F = .Self.(HasParams(.E, .E, .E, .E).V).A and
+       .E = .Self.(HasParams(.D, .D, .D, .D).V).A and
+       .D = .Self.(HasParams(.C, .C, .C, .C).V).A and
+       .C = .Self.(HasParams(.B, .B, .B, .B).V).A and
+       .B = .Self.(HasParams(.A, .A, .A, .A).V).A and
+       .A = .Self and .V = .Self](x: X) -> X.F { return x; }
+
+impl i32 as HasTypes
+  where .A = .B and .B = .C and .C = .D and .D = .E and .E = .F and .F = i32 {}
+impl i32 as HasParams(i32, i32, i32, i32) where .V = i32 {}
+
+fn Main() -> i32 {
+  return F(0);
+}
diff --git a/toolchain/semantics/fuzzer_corpus/0447b0030b48fa60d3d9f9c9163d05acd789796f b/toolchain/semantics/fuzzer_corpus/0447b0030b48fa60d3d9f9c9163d05acd789796f
new file mode 100644
index 000000000000..5d4448e346a0
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/0447b0030b48fa60d3d9f9c9163d05acd789796f
@@ -0,0 +1,22 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+package ExplorerTest api;
+
+__mixin M1 {
+  fn F1[self: Self](x: Self) -> Self{
+     return x;
+  }
+  // CHECK:STDERR: COMPILATION ERROR: fail_recursive_mixing.carbon:[[@LINE+1]]: incomplete mixin `M1` used in mix declaration
+  __mix M1;
+}
+
+class C {
+  __mix M1;
+}
+
+fn Main() -> i32 {
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/0686bcb78820140c8d024e5b7d35adaa5eec3621 b/toolchain/semantics/fuzzer_corpus/0686bcb78820140c8d024e5b7d35adaa5eec3621
new file mode 100644
index 000000000000..b0016de3d3d8
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/0686bcb78820140c8d024e5b7d35adaa5eec3621
@@ -0,0 +1,26 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+choice Ints {
+  None,
+  One(i32),
+  Two(i32, i32)
+}
+
+fn Main() -> i32 {
+  let (var Ints.Two(a1: auto, var a2: auto),
+       ((b: auto, var c: auto), var (d: auto, e: auto))) =
+      (Ints.Two(1, 10), ((2, 3), (4, 5)));
+  a1 = 0;
+  a2 = 0;
+  c = 0;
+  d = 0;
+  e = 0;
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/08187c797a711bdfbd1e48edcba3d9102766cb9d b/toolchain/semantics/fuzzer_corpus/08187c797a711bdfbd1e48edcba3d9102766cb9d
new file mode 100644
index 000000000000..f80e7d911a92
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/08187c797a711bdfbd1e48edcba3d9102766cb9d
@@ -0,0 +1,16 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+fn ReturnSecond(_: i32, x: i32) -> i32 {
+  return x;
+}
+
+fn Main() -> i32 {
+  return ReturnSecond(1, 0);
+}
diff --git a/toolchain/semantics/fuzzer_corpus/086087f87f7a0618c32aaf7e1d9fb0408e54a448 b/toolchain/semantics/fuzzer_corpus/086087f87f7a0618c32aaf7e1d9fb0408e54a448
new file mode 100644
index 000000000000..f34df1d7e132
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/086087f87f7a0618c32aaf7e1d9fb0408e54a448
@@ -0,0 +1,22 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+class Point(T:! type) {
+  fn Create(x: T, y: T) -> Point(T) {
+    return {.x = x, .y = y};
+  }
+
+  var x: T;
+  var y: T;
+}
+
+fn Main() -> i32 {
+  // CHECK:STDERR: COMPILATION ERROR: fail_generic_class_arg.carbon:[[@LINE+1]]: wrong number of arguments in function call, expected 1 but got 2
+  var p: Point(i32) = Point(i32, i32).Create(0, 1);
+  return p.x;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/0896c31a99907299ead911e234074c472a70de30 b/toolchain/semantics/fuzzer_corpus/0896c31a99907299ead911e234074c472a70de30
new file mode 100644
index 000000000000..4ae60885e677
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/0896c31a99907299ead911e234074c472a70de30
@@ -0,0 +1,18 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+// Test a global variable depending on another global.
+
+var x: i32 = 0;
+
+var y: i32 = x;
+
+fn Main() -> i32 {
+  return y;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/08ea37d96dee020359a3cd25344d9b33b23fbe8c b/toolchain/semantics/fuzzer_corpus/08ea37d96dee020359a3cd25344d9b33b23fbe8c
new file mode 100644
index 000000000000..eee03b2060b2
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/08ea37d96dee020359a3cd25344d9b33b23fbe8c
@@ -0,0 +1,15 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  // CHECK:STDERR: SYNTAX ERROR: fail_newline.carbon:[[@LINE+2]]: missing closing quote in single-line string: "new
+  // CHECK:STDERR:
+  Print("new
+line");
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/091db65a1b8f6119b3ba148eccc667ac14e7b9b5 b/toolchain/semantics/fuzzer_corpus/091db65a1b8f6119b3ba148eccc667ac14e7b9b5
new file mode 100644
index 000000000000..9f8460dd6527
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/091db65a1b8f6119b3ba148eccc667ac14e7b9b5
@@ -0,0 +1,16 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 1
+
+package ExplorerTest api;
+
+fn snd[T:! type](x: i32, y: T) -> T {
+  return y;
+}
+
+fn Main() -> i32 {
+  return snd(0, 1);
+}
diff --git a/toolchain/semantics/fuzzer_corpus/0a16a746ed273e210abe5ee6cd3c63a475479a39 b/toolchain/semantics/fuzzer_corpus/0a16a746ed273e210abe5ee6cd3c63a475479a39
new file mode 100644
index 000000000000..49262ef0b7a3
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/0a16a746ed273e210abe5ee6cd3c63a475479a39
@@ -0,0 +1,33 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+interface Iface {
+  let T:! type;
+}
+
+fn F[T:! Iface where .T == i32](x: T) {}
+
+fn G[U:! Iface where .T == i32](x: U) {
+  F(x);
+}
+
+fn H[V:! Iface](x: V) {
+  // CHECK:STDERR: COMPILATION ERROR: fail_equal_to_dependent_type.carbon:[[@LINE+1]]: constraint requires that (T).(Iface.T) (with value (V).(Iface.T)) == i32, which is not known to be true
+  F(x);
+}
+
+class Class {
+  extend impl as Iface where .T = i32 {}
+}
+
+fn Main() -> i32 {
+  var x: Class = {};
+  G(x);
+  H(x);
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/0ad9d1e319b4e0ff9813edf6706823127c78cca5 b/toolchain/semantics/fuzzer_corpus/0ad9d1e319b4e0ff9813edf6706823127c78cca5
new file mode 100644
index 000000000000..6cb9027dc7cd
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/0ad9d1e319b4e0ff9813edf6706823127c78cca5
@@ -0,0 +1,18 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 1
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  returned var x: i32 = 1;
+  if (true) {
+    var x: i32 = 2;
+    return var;
+  }
+  x = 3;
+  return var;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/0c6afa669d8b0036a28c74fa19c7370515938300 b/toolchain/semantics/fuzzer_corpus/0c6afa669d8b0036a28c74fa19c7370515938300
new file mode 100644
index 000000000000..3bb6f24e8f75
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/0c6afa669d8b0036a28c74fa19c7370515938300
@@ -0,0 +1,16 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+class C {}
+
+// CHECK:STDERR: COMPILATION ERROR: fail_combine_rhs.carbon:[[@LINE+1]]: expected a constraint in second operand of `&`, found class C
+fn F[T:! type & C]();
+
+fn Main() -> i32 {
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/0d8919c02ea985fe0c9e02b75d4d01ac98e1ada7 b/toolchain/semantics/fuzzer_corpus/0d8919c02ea985fe0c9e02b75d4d01ac98e1ada7
new file mode 100644
index 000000000000..e56388f33abf
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/0d8919c02ea985fe0c9e02b75d4d01ac98e1ada7
@@ -0,0 +1,13 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  // CHECK:STDERR: COMPILATION ERROR: fail_no_impl.carbon:[[@LINE+1]]: i32 is not equality comparable with String (could not find implementation of interface EqWith(U = String) for i32)
+  Print("different types equal: {0}", if 1 == "1" then 1 else 0);
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/0e4dff74694458253dfba70df99260d46c4f7049 b/toolchain/semantics/fuzzer_corpus/0e4dff74694458253dfba70df99260d46c4f7049
new file mode 100644
index 000000000000..e125ccb7cf43
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/0e4dff74694458253dfba70df99260d46c4f7049
@@ -0,0 +1,14 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  var x: i32;
+  // CHECK:STDERR: COMPILATION ERROR: fail_compound_assign.carbon:[[@LINE+1]]: use of uninitialized variable x
+  x += 1;
+  return x;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/0f16578e125b372618b0f999fa14d20e64baa5c5 b/toolchain/semantics/fuzzer_corpus/0f16578e125b372618b0f999fa14d20e64baa5c5
new file mode 100644
index 000000000000..c2248734ce4c
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/0f16578e125b372618b0f999fa14d20e64baa5c5
@@ -0,0 +1,42 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: A
+// CHECK:STDOUT: c.a: 1
+// CHECK:STDOUT: c.b: 2
+// CHECK:STDOUT: c.c: 3
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+base class A {
+  fn FunctionA() {}
+  var a: i32;
+  var aa: String;
+}
+
+base class B {
+  extend base: A;
+  fn FunctionB() {}
+  var b: i32;
+}
+
+class C {
+  extend base: B;
+  fn FunctionC() {}
+  var c: i32;
+}
+
+fn Main() -> i32 {
+  var c: C = {.base={.base={.aa="A", .a=1}, .b=2, }, .c=3};
+  c.FunctionA();
+  c.FunctionB();
+  c.FunctionC();
+  Print(c.aa);
+  Print("c.a: {0}", c.a);
+  Print("c.b: {0}", c.b);
+  Print("c.c: {0}", c.c);
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/0f51cb18d302c1493cbf5389ca74fa97a49090c5 b/toolchain/semantics/fuzzer_corpus/0f51cb18d302c1493cbf5389ca74fa97a49090c5
new file mode 100644
index 000000000000..5d5f7ac8242a
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/0f51cb18d302c1493cbf5389ca74fa97a49090c5
@@ -0,0 +1,23 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 1
+
+package ExplorerTest api;
+
+class Point(T:! type, V:! T) {
+  fn Get[self: Self]() -> T {
+    return V;
+  }
+}
+
+fn F(p: Point(i32, 1)) -> i32 {
+  return p.Get();
+}
+
+fn Main() -> i32 {
+  var v: Point(i32, 1) = {};
+  return F(v);
+}
diff --git a/toolchain/semantics/fuzzer_corpus/1016cb8abba49330ca337c3c650f8b887a8eec56 b/toolchain/semantics/fuzzer_corpus/1016cb8abba49330ca337c3c650f8b887a8eec56
new file mode 100644
index 000000000000..82570013a8f6
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/1016cb8abba49330ca337c3c650f8b887a8eec56
@@ -0,0 +1,41 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+interface Vector {
+  fn Add[self: Self](b: Self) -> Self;
+  fn Scale[self: Self](v: i32) -> Self;
+}
+
+class Point {
+  var x: i32;
+  var y: i32;
+  extend impl as Vector {
+    fn Add[self: Point](b: Point) -> Point {
+      return {.x = self.x + b.x, .y = self.y + b.y};
+    }
+    fn Scale[self: Point](v: i32) -> Point {
+      return {.x = self.x * v, .y = self.y * v};
+    }
+  }
+}
+
+fn ScaleGeneric[U:! Vector](c: U, s: i32) -> U {
+  return c.Scale(s);
+}
+
+fn AddAndScaleGeneric[T:! Vector](a: T, b: T, s: i32) -> T {
+  return ScaleGeneric(a.Add(b), s);
+}
+
+fn Main() -> i32 {
+  var a: Point = {.x = 1, .y = 1};
+  var b: Point = {.x = 2, .y = 3};
+  var p: Point = AddAndScaleGeneric(a, b, 5);
+  return p.x - 15;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/105bf041eb0ec468660023a131981170036c4aa4 b/toolchain/semantics/fuzzer_corpus/105bf041eb0ec468660023a131981170036c4aa4
new file mode 100644
index 000000000000..ad06d1e3be4f
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/105bf041eb0ec468660023a131981170036c4aa4
@@ -0,0 +1,19 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+fn CompareStr(s: String) -> i32 {
+  if (s == ##"str"##) {
+    return 0;
+  }
+  return 1;
+}
+
+fn Main() -> i32 {
+  return CompareStr(#####"str"#####);
+}
diff --git a/toolchain/semantics/fuzzer_corpus/10d1744fbabedd2d7b67aeeba5ccfad33dde54eb b/toolchain/semantics/fuzzer_corpus/10d1744fbabedd2d7b67aeeba5ccfad33dde54eb
new file mode 100644
index 000000000000..8e5514e31611
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/10d1744fbabedd2d7b67aeeba5ccfad33dde54eb
@@ -0,0 +1,28 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+// TODO: Implement this with some kind of reflection?
+impl {.x: i32, .y: i32} as EqWith(Self) {
+  fn Equal[self: Self](other: Self) -> bool {
+    return self.x == other.x and self.y == other.y;
+  }
+  fn NotEqual[self: Self](other: Self) -> bool {
+    return self.x != other.x or self.y != other.y;
+  }
+}
+
+fn Main() -> i32 {
+  var t1: {.x: i32, .y: i32} = {.x = 5, .y = 2};
+  var t2: {.x: i32,} = {.x = 5,};
+  // CHECK:STDERR: COMPILATION ERROR: fail_equality_type.carbon:[[@LINE+1]]: {.x: i32, .y: i32} is not equality comparable with {.x: i32} (could not find implementation of interface EqWith(U = {.x: i32}) for {.x: i32, .y: i32})
+  if (t1 == t2) {
+    return 1;
+  } else {
+    return 0;
+  }
+}
diff --git a/toolchain/semantics/fuzzer_corpus/10ed248ac6874c3c6ee8fed1ffff5e2d4f0c5ec5 b/toolchain/semantics/fuzzer_corpus/10ed248ac6874c3c6ee8fed1ffff5e2d4f0c5ec5
new file mode 100644
index 000000000000..914675479276
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/10ed248ac6874c3c6ee8fed1ffff5e2d4f0c5ec5
@@ -0,0 +1,17 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+fn F() {}
+alias A = F;
+
+// CHECK:STDERR: COMPILATION ERROR: fail_wrong_fn_alias_use.carbon:[[@LINE+1]]: alias A cannot be used as a name qualifier
+fn A.Foo() {}
+
+fn Main() -> i32 {
+    return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/1171a926d8aa677aec7042fe5f9e29c1632f5300 b/toolchain/semantics/fuzzer_corpus/1171a926d8aa677aec7042fe5f9e29c1632f5300
new file mode 100644
index 000000000000..2d6a1df0bd49
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/1171a926d8aa677aec7042fe5f9e29c1632f5300
@@ -0,0 +1,17 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package EmptyIdentifier impl;
+
+fn A() {
+  // CHECK:STDERR: RUNTIME ERROR: fail_function_recursion.carbon:[[@LINE+1]]: stack overflow: too many interpreter actions on stack
+  A();
+}
+
+fn Main() -> i32 {
+  A();
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/119ac0fd33bccc1f9d8d4c78f485db62b8261039 b/toolchain/semantics/fuzzer_corpus/119ac0fd33bccc1f9d8d4c78f485db62b8261039
new file mode 100644
index 000000000000..9e166d23cc84
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/119ac0fd33bccc1f9d8d4c78f485db62b8261039
@@ -0,0 +1,14 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  var x: i32;
+  // CHECK:STDERR: COMPILATION ERROR: fail_rhs_def.carbon:[[@LINE+1]]: use of uninitialized variable x
+  var y: i32 = x;
+  return x;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/119e4e694e8b998c45200f2f9bba291c8f18de86 b/toolchain/semantics/fuzzer_corpus/119e4e694e8b998c45200f2f9bba291c8f18de86
new file mode 100644
index 000000000000..0c94487e789f
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/119e4e694e8b998c45200f2f9bba291c8f18de86
@@ -0,0 +1,16 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  var a: i32 = 1;
+  let a_pinned: i32 = a;
+  // OK: Value unused after being mutated.
+  a = 2;
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/1259d0decfb6c2fd6808fda42a9654bbad1640de b/toolchain/semantics/fuzzer_corpus/1259d0decfb6c2fd6808fda42a9654bbad1640de
new file mode 100644
index 000000000000..5c6264444b2b
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/1259d0decfb6c2fd6808fda42a9654bbad1640de
@@ -0,0 +1,45 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: DESTRUCTOR A 1
+// CHECK:STDOUT: DESTRUCTOR A 2
+// CHECK:STDOUT: DESTRUCTOR A 3
+// CHECK:STDOUT: DESTRUCTOR A 4
+// CHECK:STDOUT: result: 2
+
+package ExplorerTest api;
+
+class A{
+    destructor[self: Self]{
+        Print("DESTRUCTOR A {0}",self.n);
+    }
+    var n: i32;
+}
+
+fn ident(x: bool)-> bool{
+    return x;
+}
+
+fn ident_i32(x: i32)-> i32{
+    return x;
+}
+// It should be enforced that different runtime scopes are on the stack.
+//So that it can be tested that the wrong scopes are not removed from the stack.
+fn Main() -> i32 {
+  var i: i32 = 0;
+  var d: A = {.n = 4};
+  if(ident(true)){
+    var a: A = {.n = 3};
+    if(true){
+       var b: A = {.n = 2};
+       ident_i32(2);
+       if(ident_i32(0) == 0){
+         var c: A = {.n = 1};
+         return 2;
+       }
+    }
+  }
+  return 1;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/128de0e2a70878988fcd7bf60bdd862ef764b92f b/toolchain/semantics/fuzzer_corpus/128de0e2a70878988fcd7bf60bdd862ef764b92f
new file mode 100644
index 000000000000..b51098000623
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/128de0e2a70878988fcd7bf60bdd862ef764b92f
@@ -0,0 +1,16 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  // CHECK:STDERR: SYNTAX ERROR: fail_raw_block_more_hash_tags_on_right.carbon:[[@LINE+1]]: invalid character '\x23' in source file.
+  var s: String = #'''
+    error: there are more #s on the right than the left.
+  '''##;
+
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/12b34eb2c07d14c7b6c964bed06d9cd9b295570a b/toolchain/semantics/fuzzer_corpus/12b34eb2c07d14c7b6c964bed06d9cd9b295570a
new file mode 100644
index 000000000000..13c2bbbd016e
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/12b34eb2c07d14c7b6c964bed06d9cd9b295570a
@@ -0,0 +1,19 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 2
+
+package ExplorerTest api;
+
+var call_count: i32 = 0;
+fn ReturnFalse() -> bool {
+  call_count = call_count + 1;
+  return false;
+}
+
+fn Main() -> i32 {
+  var result: bool = ReturnFalse() or ReturnFalse();
+  return if not result then call_count else -1;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/137565f0078baddcd33c03bcb752cd91e0c15195 b/toolchain/semantics/fuzzer_corpus/137565f0078baddcd33c03bcb752cd91e0c15195
new file mode 100644
index 000000000000..ecd4920bb8d2
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/137565f0078baddcd33c03bcb752cd91e0c15195
@@ -0,0 +1,17 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+abstract class B {
+}
+
+// CHECK:STDERR: COMPILATION ERROR: fail_instantiate_global_abstract.carbon:[[@LINE+1]]: Cannot instantiate abstract class B
+var b: B = {};
+
+fn Main() -> i32 {
+    return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/13936e89e497ed4f7b0555ad0fe8142c71385208 b/toolchain/semantics/fuzzer_corpus/13936e89e497ed4f7b0555ad0fe8142c71385208
new file mode 100644
index 000000000000..bd575721370c
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/13936e89e497ed4f7b0555ad0fe8142c71385208
@@ -0,0 +1,17 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+fn add1(x: i32) -> i32 {
+  return x + 1;
+}
+
+fn Main() -> i32 {
+  var f: __Fn(i32)->i32 = add1;
+  return f(-1);
+}
diff --git a/toolchain/semantics/fuzzer_corpus/1397a4fbdf1addb0892345321c7fbc14adf77b4c b/toolchain/semantics/fuzzer_corpus/1397a4fbdf1addb0892345321c7fbc14adf77b4c
new file mode 100644
index 000000000000..76b4f3c180a2
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/1397a4fbdf1addb0892345321c7fbc14adf77b4c
@@ -0,0 +1,24 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+interface Has(T:! type) {
+  fn Get() -> T;
+}
+impl i32 as Has(type) {
+  fn Get() -> type { return Self; }
+}
+
+class WithType(T:! Has(type)) {
+  fn Get() -> type { return T.Get(); }
+}
+
+fn Main() -> i32 {
+  var v: WithType(i32).Get() = 0;
+  return v;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/14bf3c7665fe5282a469b474df3d2485550adbd4 b/toolchain/semantics/fuzzer_corpus/14bf3c7665fe5282a469b474df3d2485550adbd4
new file mode 100644
index 000000000000..10bd559201d0
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/14bf3c7665fe5282a469b474df3d2485550adbd4
@@ -0,0 +1,14 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+constraint X {
+  // CHECK:STDERR: COMPILATION ERROR: fail_associated_constant.carbon:[[@LINE+1]]: associated constant not permitted in named constraint
+  let N:! type;
+}
+
+fn Main() -> i32 { return 0; }
diff --git a/toolchain/semantics/fuzzer_corpus/1554c1eb73ff3932ad2e83351d6b0c98fca9492c b/toolchain/semantics/fuzzer_corpus/1554c1eb73ff3932ad2e83351d6b0c98fca9492c
new file mode 100644
index 000000000000..bba45c3d6211
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/1554c1eb73ff3932ad2e83351d6b0c98fca9492c
@@ -0,0 +1,19 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+fn CompareStr(s: String) -> i32 {
+  if (s == "str;\x07") {
+    return 0;
+  }
+  return 1;
+}
+
+fn Main() -> i32 {
+  return CompareStr("\x73\x74\x72\x3B\x07");
+}
diff --git a/toolchain/semantics/fuzzer_corpus/164cd743faa60d9495a35aeeaaac5ebcbaaed5c8 b/toolchain/semantics/fuzzer_corpus/164cd743faa60d9495a35aeeaaac5ebcbaaed5c8
new file mode 100644
index 000000000000..383a6f1896a7
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/164cd743faa60d9495a35aeeaaac5ebcbaaed5c8
@@ -0,0 +1,12 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  // CHECK:STDERR: COMPILATION ERROR: fail_destination_not_type.carbon:[[@LINE+1]]: type error in type expression: 'i32' is not implicitly convertible to 'type'
+  return 4 as 7;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/17ec5002557db4205de08c6daad9a3f6cb529076 b/toolchain/semantics/fuzzer_corpus/17ec5002557db4205de08c6daad9a3f6cb529076
new file mode 100644
index 000000000000..3600b36cc6a3
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/17ec5002557db4205de08c6daad9a3f6cb529076
@@ -0,0 +1,22 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 1
+
+package ExplorerTest api;
+
+fn IntDiff(a: i32, b: i32) -> i32 {
+  if (a == b) {
+    returned var ret: i32 = a - b;
+    return var;
+  } else {
+    returned var ret2: i32 = b - a;
+    return var;
+  }
+}
+
+fn Main() -> i32 {
+  return IntDiff(1, 2);
+}
diff --git a/toolchain/semantics/fuzzer_corpus/188ed5d12d9c374702dfc38ab438dfe4b8cbabfd b/toolchain/semantics/fuzzer_corpus/188ed5d12d9c374702dfc38ab438dfe4b8cbabfd
new file mode 100644
index 000000000000..cf224b8f9a76
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/188ed5d12d9c374702dfc38ab438dfe4b8cbabfd
@@ -0,0 +1,46 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: c.Foo() -> 1
+// CHECK:STDOUT: c.Bar() -> 2
+// CHECK:STDOUT: d.Foo() -> 3
+// CHECK:STDOUT: d.Bar() -> 4
+// CHECK:STDOUT: cc.Foo() -> 3
+// CHECK:STDOUT: cc.Bar() -> 2
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+base class C {
+  virtual fn Foo[self: Self]() -> i32 {
+    return 1;
+  }
+  fn Bar[self: Self]() -> i32 {
+    return 2;
+  }
+}
+
+class D {
+  extend base: C;
+  impl fn Foo[self: Self]() -> i32 {
+    return 3;
+  }
+  fn Bar[self: Self]() -> i32 {
+    return 4;
+  }
+}
+
+fn Main() -> i32 {
+  var c: C = {};
+  Print("c.Foo() -> {0}", c.Foo());
+  Print("c.Bar() -> {0}", c.Bar());
+  var d: D = {.base = {}};
+  Print("d.Foo() -> {0}", d.Foo());
+  Print("d.Bar() -> {0}", d.Bar());
+  var cc: C* = &d;
+  Print("cc.Foo() -> {0}", (*cc).Foo());
+  Print("cc.Bar() -> {0}", (*cc).Bar());
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/18ec728eade91679104b23c3a949271089132321 b/toolchain/semantics/fuzzer_corpus/18ec728eade91679104b23c3a949271089132321
new file mode 100644
index 000000000000..ebeaeefe12e9
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/18ec728eade91679104b23c3a949271089132321
@@ -0,0 +1,19 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+class Point {
+  var x: i32;
+  var y: i32;
+}
+
+var p: Point = {.x = 1, .y = 2};
+
+fn Main() -> i32 {
+  return p.y - p.x - 1;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/1913a5458321a159544fff949d3f7b0f9d52065a b/toolchain/semantics/fuzzer_corpus/1913a5458321a159544fff949d3f7b0f9d52065a
new file mode 100644
index 000000000000..f0faf2e26524
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/1913a5458321a159544fff949d3f7b0f9d52065a
@@ -0,0 +1,16 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+fn fst[T:! type](x: T, y: T) -> T {
+  return x;
+}
+
+fn Main() -> i32 {
+  return fst(0, 1);
+}
diff --git a/toolchain/semantics/fuzzer_corpus/19d6f8cf04b59808515a78af96abc89cd4c2583e b/toolchain/semantics/fuzzer_corpus/19d6f8cf04b59808515a78af96abc89cd4c2583e
new file mode 100644
index 000000000000..6bd5f56a56d1
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/19d6f8cf04b59808515a78af96abc89cd4c2583e
@@ -0,0 +1,21 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+class C {
+  fn F() {}
+  fn G[self: Self]() {}
+}
+
+fn H[T:! type](x: T) {}
+
+fn Main() -> i32 {
+  H(C.F);
+  // CHECK:STDERR: COMPILATION ERROR: fail_method_deduced.carbon:[[@LINE+1]]: member name G can only be used in a member access or alias
+  H(C.G);
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/1ad7c0030d4448143955e4e047868426e46a08e6 b/toolchain/semantics/fuzzer_corpus/1ad7c0030d4448143955e4e047868426e46a08e6
new file mode 100644
index 000000000000..60a2677ef4b1
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/1ad7c0030d4448143955e4e047868426e46a08e6
@@ -0,0 +1,14 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  var x: i32;
+  // CHECK:STDERR: COMPILATION ERROR: fail_field_value.carbon:[[@LINE+1]]: use of uninitialized variable x
+  var p: auto = {.x = x,};
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/1af0cf0cfeabefdff968d557c1b67a32a424f357 b/toolchain/semantics/fuzzer_corpus/1af0cf0cfeabefdff968d557c1b67a32a424f357
new file mode 100644
index 000000000000..702247213d8a
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/1af0cf0cfeabefdff968d557c1b67a32a424f357
@@ -0,0 +1,14 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 1
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  var x: i32;
+  x = 1;
+  return x;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/1b5911a616ba8ae35eb39f855270fa9b766c3afc b/toolchain/semantics/fuzzer_corpus/1b5911a616ba8ae35eb39f855270fa9b766c3afc
new file mode 100644
index 000000000000..1fa446a9f608
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/1b5911a616ba8ae35eb39f855270fa9b766c3afc
@@ -0,0 +1,44 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: Foo(c1): 1
+// CHECK:STDOUT: Foo(c2): 1
+// CHECK:STDOUT: Foo(d): 1
+// CHECK:STDOUT: Foo(&e): 1
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+base class C {
+  var val: i32;
+}
+
+base class D {
+  extend base: C;
+  var val: i32;
+}
+
+class E {
+  extend base: D;
+  var val: i32;
+}
+
+fn Foo(c: C*) -> i32 {
+  return (*c).val;
+}
+
+fn Main() -> i32 {
+  var e: E = { .val = 3, .base = {.val = 2,.base = {.val = 1}}};
+  var d: D* = &e;
+  var c1: C* = &e;
+  var c2: C* = d;
+
+  Print("Foo(c1): {0}", Foo(c1));
+  Print("Foo(c2): {0}", Foo(c2));
+  Print("Foo(d): {0}", Foo(d));
+  Print("Foo(&e): {0}", Foo(&e));
+
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/1c939f5777f53aaf53300f4e54c1f2380b8b4f6a b/toolchain/semantics/fuzzer_corpus/1c939f5777f53aaf53300f4e54c1f2380b8b4f6a
new file mode 100644
index 000000000000..4bdf729d8ee5
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/1c939f5777f53aaf53300f4e54c1f2380b8b4f6a
@@ -0,0 +1,34 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: 1
+// CHECK:STDOUT: 2
+// CHECK:STDOUT: 3
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+base class A {
+  var a: i32;
+}
+
+base class B {
+  extend base: A;
+  var b: i32;
+}
+
+class C {
+  extend base: B;
+  var c: i32;
+}
+
+fn Main() -> i32 {
+  var c: C = {.base = {.base = {.a = 1}, .b = 2}, .c = 3};
+  let (pa: A*, pb: B*, pc: C*) = (&c, &c, &c);
+  Print("{0}", pa->a);
+  Print("{0}", pb->b);
+  Print("{0}", pc->c);
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/1d5b8ef87c518dfd90dfaf7e98886a4ef791ab93 b/toolchain/semantics/fuzzer_corpus/1d5b8ef87c518dfd90dfaf7e98886a4ef791ab93
new file mode 100644
index 000000000000..a949a82d457d
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/1d5b8ef87c518dfd90dfaf7e98886a4ef791ab93
@@ -0,0 +1,37 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: Class 1
+// CHECK:STDOUT: Class 2
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+base class C {
+  fn BasePrint(v: i32) {
+    Print("Class {0}", v);
+  }
+  fn Method1[self: Self]() {
+    self.BasePrint(self.value_c);
+  }
+
+  var value_c: i32;
+}
+
+class D {
+  extend base: C;
+  fn Method2[self: Self]() {
+    self.BasePrint(self.value_d);
+  }
+
+  var value_d: i32;
+}
+
+fn Main() -> i32 {
+  var d: D = {.base = {.value_c = 1}, .value_d = 2};
+  d.Method1();
+  d.Method2();
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/1d6d70723cfa13913d715a7ba2d7efa03d521df9 b/toolchain/semantics/fuzzer_corpus/1d6d70723cfa13913d715a7ba2d7efa03d521df9
new file mode 100644
index 000000000000..fcba0882728d
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/1d6d70723cfa13913d715a7ba2d7efa03d521df9
@@ -0,0 +1,55 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+interface Vector {
+  fn Add[self: Self](b: Self) -> Self;
+  fn Scale[self: Self](v: i32) -> Self;
+}
+
+class Point1 {
+  var x: i32;
+  var y: i32;
+  extend impl as Vector {
+    fn Add[self: Point1](b: Point1) -> Point1 {
+      return {.x = self.x + b.x, .y = self.y + b.y};
+    }
+    fn Scale[self: Point1](v: i32) -> Point1 {
+      return {.x = self.x * v, .y = self.y * v};
+    }
+  }
+}
+
+class Point2 {
+  var x: i32;
+  var y: i32;
+  extend impl as Vector {
+    fn Add[self: Point2](b: Point2) -> Point2 {
+      return {.x = self.x + b.x + 1, .y = self.y + b.y + 1};
+    }
+    fn Scale[self: Point2](v: i32) -> Point2 {
+      return {.x = self.x * v * 2, .y = self.y * v * 2};
+    }
+  }
+}
+
+fn ScaleGeneric[U:! Vector](c: U, s: i32) -> U {
+  return c.Scale(s);
+}
+
+fn AddAndScaleGeneric[T:! Vector, V:! Vector](a: T, b: V, s: i32) -> (T, V) {
+  return (ScaleGeneric(a.Add(a), s),
+  	  ScaleGeneric(b.Add(b), s));
+}
+
+fn Main() -> i32 {
+  var a: Point1 = {.x = 1, .y = 1};
+  var b: Point2 = {.x = 2, .y = 3};
+  var (p: Point1, q: Point2) = AddAndScaleGeneric(a, b, 5);
+  return q.x - p.x - 40;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/1dddc76f0ab71e0db413ccbd3eb8440ce69fe0e0 b/toolchain/semantics/fuzzer_corpus/1dddc76f0ab71e0db413ccbd3eb8440ce69fe0e0
new file mode 100644
index 000000000000..55917600e6a0
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/1dddc76f0ab71e0db413ccbd3eb8440ce69fe0e0
@@ -0,0 +1,25 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+interface Iface {
+  let N:! i32;
+}
+
+fn F(T:! Iface where .N == 5) {}
+
+class Good {}
+class Bad {}
+impl Good as Iface where .N = 5 {}
+impl Bad as Iface where .N = 4 {}
+
+fn Main() -> i32 {
+  F(Good);
+  // CHECK:STDERR: COMPILATION ERROR: fail_different_value.carbon:[[@LINE+1]]: constraint requires that (T).(Iface.N) (with value 4) == 5, which is not known to be true
+  F(Bad);
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/1e4c94040dcf313929b6e45bb96932198f296d9e b/toolchain/semantics/fuzzer_corpus/1e4c94040dcf313929b6e45bb96932198f296d9e
new file mode 100644
index 000000000000..625dc56c9858
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/1e4c94040dcf313929b6e45bb96932198f296d9e
@@ -0,0 +1,18 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 4
+
+package ExplorerTest api;
+
+alias TypeAlias = i32;
+
+fn Main() -> TypeAlias {
+  var n: TypeAlias = 1;
+  var m: i32 = n;
+  var p: i32* = &n;
+  var q: TypeAlias* = &m;
+  return *p + *q + m + n;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/1ee86793bb703120496039d708f7562e9abfbc5c b/toolchain/semantics/fuzzer_corpus/1ee86793bb703120496039d708f7562e9abfbc5c
new file mode 100644
index 000000000000..31427690b9f9
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/1ee86793bb703120496039d708f7562e9abfbc5c
@@ -0,0 +1,16 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+fn F() {}
+
+// CHECK:STDERR: COMPILATION ERROR: fail_qualifier_not_namespace.carbon:[[@LINE+1]]: fn F cannot be used as a name qualifier
+fn F.G() {}
+
+fn Main() -> i32 {
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/1f287f6a07c7bf4e14bd2563f2877e1ca28c52c3 b/toolchain/semantics/fuzzer_corpus/1f287f6a07c7bf4e14bd2563f2877e1ca28c52c3
new file mode 100644
index 000000000000..ac4b65305ada
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/1f287f6a07c7bf4e14bd2563f2877e1ca28c52c3
@@ -0,0 +1,13 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  Assert(true, "HALLO WELT");
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/1fc793d170552ec217bfa6554c43444b5bc1a30d b/toolchain/semantics/fuzzer_corpus/1fc793d170552ec217bfa6554c43444b5bc1a30d
new file mode 100644
index 000000000000..f8db3b2fbe66
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/1fc793d170552ec217bfa6554c43444b5bc1a30d
@@ -0,0 +1,46 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: 6
+// CHECK:STDOUT: 5
+// CHECK:STDOUT: 6
+// CHECK:STDOUT: 5
+// CHECK:STDOUT: 6
+// CHECK:STDOUT: 5
+// CHECK:STDOUT: 6
+// CHECK:STDOUT: 5
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+class A { var n: i32; }
+
+impl A as Inc {
+  fn Op[addr self: Self*]() { ++self->n; }
+}
+impl A as Dec {
+  fn Op[addr self: Self*]() { --self->n; }
+}
+
+fn Main() -> i32 {
+  var a: A = {.n = 5};
+  ++a.n;
+  Print("{0}", a.n);
+  --a.n;
+  Print("{0}", a.n);
+  ++a;
+  Print("{0}", a.n);
+  --a;
+  Print("{0}", a.n);
+  a.n.(Inc.Op)();
+  Print("{0}", a.n);
+  a.n.(Dec.Op)();
+  Print("{0}", a.n);
+  a.(Inc.Op)();
+  Print("{0}", a.n);
+  a.(Dec.Op)();
+  Print("{0}", a.n);
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/2038a206d7fa99068235bb2ba54820e768b29cb9 b/toolchain/semantics/fuzzer_corpus/2038a206d7fa99068235bb2ba54820e768b29cb9
new file mode 100644
index 000000000000..23ef654fbd7d
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/2038a206d7fa99068235bb2ba54820e768b29cb9
@@ -0,0 +1,18 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 1
+
+package Foo api;
+interface A { fn F[self: Self]() -> i32; }
+class X {
+  extend impl as A {
+    fn F[self: Self]() -> i32 { return 1; }
+  }
+}
+fn Main() -> i32 {
+  var a: X = {};
+  return a.(X.(A.F))();
+}
diff --git a/toolchain/semantics/fuzzer_corpus/20bbc444ffd3b0a688732fe0aa1eeff6969c33cc b/toolchain/semantics/fuzzer_corpus/20bbc444ffd3b0a688732fe0aa1eeff6969c33cc
new file mode 100644
index 000000000000..296d4d1132c3
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/20bbc444ffd3b0a688732fe0aa1eeff6969c33cc
@@ -0,0 +1,13 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest impl;
+
+fn Main() -> i32 {
+  // CHECK:STDERR: RUNTIME ERROR: fail_single_brace.carbon:[[@LINE+1]]: `{` must be followed by a second `{` or index in `{`
+  Print("{");
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/21e0d305628d54204f02591a43b61527cda5d976 b/toolchain/semantics/fuzzer_corpus/21e0d305628d54204f02591a43b61527cda5d976
new file mode 100644
index 000000000000..9816b7c8dc4c
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/21e0d305628d54204f02591a43b61527cda5d976
@@ -0,0 +1,12 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+// CHECK:STDERR: COMPILATION ERROR: fail_nontype_tuple_as_type.carbon:[[@LINE+1]]: type error in type of name binding: '(i32, i32)' is not implicitly convertible to 'type'
+fn F[T:! (i32, i32)](x: T);
+
+fn Main() -> i32;
diff --git a/toolchain/semantics/fuzzer_corpus/22d9a3333ee8d54f7e1233bf62920026ca8f3a1d b/toolchain/semantics/fuzzer_corpus/22d9a3333ee8d54f7e1233bf62920026ca8f3a1d
new file mode 100644
index 000000000000..29428f43db77
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/22d9a3333ee8d54f7e1233bf62920026ca8f3a1d
@@ -0,0 +1,21 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+interface X { fn F(); }
+impl i32 as X { fn F() {} }
+
+fn G[T:! X](v: T) -> type {
+  v.F();
+  return i32;
+}
+
+fn Main() -> i32 {
+  var v: G(0) = 0;
+  return v;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/23e9f18ca5b5c85f4a44e3c472bbd23d1420013b b/toolchain/semantics/fuzzer_corpus/23e9f18ca5b5c85f4a44e3c472bbd23d1420013b
new file mode 100644
index 000000000000..73dea8d9b58d
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/23e9f18ca5b5c85f4a44e3c472bbd23d1420013b
@@ -0,0 +1,13 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest impl;
+
+fn Main() -> i32 {
+  // CHECK:STDERR: RUNTIME ERROR: fail_index_bounds1.carbon:[[@LINE+1]]: Index invalid with argument count of 1 at offset 12 in `Print: {0} {1}`
+  Print("Print: {0} {1}", 1);
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/2464b8df7ccb3280edff4bce116483b5b165a953 b/toolchain/semantics/fuzzer_corpus/2464b8df7ccb3280edff4bce116483b5b165a953
new file mode 100644
index 000000000000..c574e7dc230b
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/2464b8df7ccb3280edff4bce116483b5b165a953
@@ -0,0 +1,14 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+fn add(x: i32, y: i32) -> auto { return x + y; }
+
+fn Main() -> i32 {
+  return add(1, 2) - 3;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/25337ce57e0a62b2091a8b41a217cc54d65d0d80 b/toolchain/semantics/fuzzer_corpus/25337ce57e0a62b2091a8b41a217cc54d65d0d80
new file mode 100644
index 000000000000..8269f1145cd7
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/25337ce57e0a62b2091a8b41a217cc54d65d0d80
@@ -0,0 +1,31 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: 8
+// CHECK:STDOUT: 4
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  if (1 << 0 != 1) { return 1; }
+  if (1 << 3 != 8) { return 2; }
+  if (0 << 3 != 0) { return 3; }
+  if (3 << 1 != 6) { return 4; }
+  if (-1 << 2 != -4) { return 5; }
+  if (1 >> 0 != 1) { return 6; }
+  if (1 >> 1 != 0) { return 7; }
+  if (3 >> 1 != 1) { return 8; }
+  if (-1 >> 1 != -1) { return 9; }
+  if (-2 >> 1 != -1) { return 10; }
+
+  var n: i32 = 1;
+  n <<= 3;
+  Print("{0}", n);
+  n >>= 1;
+  Print("{0}", n);
+
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/25502eb01b8fec80bd8f99258c8e2c4db7ebd1dd b/toolchain/semantics/fuzzer_corpus/25502eb01b8fec80bd8f99258c8e2c4db7ebd1dd
new file mode 100644
index 000000000000..9c41ed48b655
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/25502eb01b8fec80bd8f99258c8e2c4db7ebd1dd
@@ -0,0 +1,13 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  // CHECK:STDERR: RUNTIME ERROR: fail_overflow_add.carbon:[[@LINE+1]]: integer overflow
+  var a: auto = 2147483647 + 1;
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/2552f1d3328f74b706d9138c53a14ff62b3b6bb3 b/toolchain/semantics/fuzzer_corpus/2552f1d3328f74b706d9138c53a14ff62b3b6bb3
new file mode 100644
index 000000000000..b046cb26ce4e
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/2552f1d3328f74b706d9138c53a14ff62b3b6bb3
@@ -0,0 +1,19 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+fn CompareStr(s: String) -> i32 {
+  if (s == "HELLO WORLD!!") {
+    return 0;
+  }
+  return 1;
+}
+
+fn Main() -> i32 {
+  return CompareStr("\u{0048}\u{0045}\u{004C}\u{004C}\u{004F} \u{0057}\u{004F}\u{0052}\u{004C}\u{0044}\u{0021}\u{21}");
+}
diff --git a/toolchain/semantics/fuzzer_corpus/26ce51c2c7f8a1d9f1b0c03722e8619f4e6eb1a5 b/toolchain/semantics/fuzzer_corpus/26ce51c2c7f8a1d9f1b0c03722e8619f4e6eb1a5
new file mode 100644
index 000000000000..472a8f4d1152
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/26ce51c2c7f8a1d9f1b0c03722e8619f4e6eb1a5
@@ -0,0 +1,16 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+class C {}
+
+// CHECK:STDERR: SYNTAX ERROR: fail_type_only.carbon:[[@LINE+1]]: syntax error, unexpected RIGHT_SQUARE_BRACKET, expecting COLON
+fn f[x:! i32, addr C]() {}
+
+fn Main() -> i32 {
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/27b81cef471374f0e9d02dcf2be5e79e45c0de2c b/toolchain/semantics/fuzzer_corpus/27b81cef471374f0e9d02dcf2be5e79e45c0de2c
new file mode 100644
index 000000000000..2999dd63533a
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/27b81cef471374f0e9d02dcf2be5e79e45c0de2c
@@ -0,0 +1,44 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+interface Vector {
+  fn Zero() -> Self;
+  fn Add[self: Self](b: Self) -> Self;
+  fn Scale[self: Self](v: i32) -> Self;
+}
+
+class Point(T:! type) {
+  var x: T;
+  var y: T;
+}
+
+impl Point(i32) as Vector {
+  // Allowed: `Self` means `Point(i32)` here.
+  fn Zero() -> Self {
+    return {.x = 0, .y = 0};
+  }
+
+  fn Add[self: Self](b: Self) -> Self {
+    return {.x = self.x + b.x, .y = self.y + b.y};
+  }
+
+  fn Scale[self: Self](v: i32) -> Self {
+    return {.x = self.x * v, .y = self.y * v};
+  }
+}
+
+fn AddAndScaleGeneric[T:! Vector](a: T, s: i32) -> T {
+  return a.Add(T.Zero()).Scale(s);
+}
+
+fn Main() -> i32 {
+  var a: Point(i32) = {.x = 2, .y = 1};
+  var p: Point(i32) = AddAndScaleGeneric(a, 5);
+  return p.x - 10;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/28720cdeeeba8921f97c137876b6dbe6e2a3225f b/toolchain/semantics/fuzzer_corpus/28720cdeeeba8921f97c137876b6dbe6e2a3225f
new file mode 100644
index 000000000000..984ded1576a5
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/28720cdeeeba8921f97c137876b6dbe6e2a3225f
@@ -0,0 +1,22 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 2
+
+package ExplorerTest api;
+
+interface Vector {
+  let Dim:! i32;
+}
+
+class Point {
+  var x: i32;
+  var y: i32;
+  extend impl as Vector where .Dim = 2 {}
+}
+
+fn Main() -> i32 {
+  return Point.(Vector.Dim);
+}
diff --git a/toolchain/semantics/fuzzer_corpus/291af82d79bec74264cef40a43fcd6198593d0b5 b/toolchain/semantics/fuzzer_corpus/291af82d79bec74264cef40a43fcd6198593d0b5
new file mode 100644
index 000000000000..eff5ba92c4ab
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/291af82d79bec74264cef40a43fcd6198593d0b5
@@ -0,0 +1,20 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 3
+
+package ExplorerTest api;
+
+class TypeLike {
+  extend impl as ImplicitAs(type) {
+    fn Convert[self: Self]() -> type { return i32; }
+  }
+  fn Make() -> Self { return {}; }
+}
+
+fn Main() -> TypeLike.Make() {
+  var x: {.a: TypeLike.Make(), .b: TypeLike.Make()} = {.a = 1, .b = 2};
+  return x.a + x.b;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/292afba18cbb0ca2936ed77ebc79534ac76eeea4 b/toolchain/semantics/fuzzer_corpus/292afba18cbb0ca2936ed77ebc79534ac76eeea4
new file mode 100644
index 000000000000..3d51f9b42bf9
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/292afba18cbb0ca2936ed77ebc79534ac76eeea4
@@ -0,0 +1,16 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  if (0 == 1) {
+    return 1;
+  }
+
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/29366dc2c3a372bec197172efb4c3b245a6b6e95 b/toolchain/semantics/fuzzer_corpus/29366dc2c3a372bec197172efb4c3b245a6b6e95
new file mode 100644
index 000000000000..f596f4832a1f
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/29366dc2c3a372bec197172efb4c3b245a6b6e95
@@ -0,0 +1,19 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package EmptyIdentifier impl;
+
+fn Main() -> i32 {
+  while (true) {
+    // Ideally we would hit an OOM here, but it's too difficult to OOM from heap
+    // allocations before hitting max steps. Maybe with string operations we
+    // could trigger actual excessive memory allocations by just doubling the
+    // size of the string each time.
+    // CHECK:STDERR: RUNTIME ERROR: fail_allocate.carbon:[[@LINE+1]]: possible infinite loop: too many interpreter steps executed
+    heap.New((0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 0));
+  }
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/293b69131b73f32057424dee21a24ea04530399a b/toolchain/semantics/fuzzer_corpus/293b69131b73f32057424dee21a24ea04530399a
new file mode 100644
index 000000000000..f8b6c2d0248b
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/293b69131b73f32057424dee21a24ea04530399a
@@ -0,0 +1,19 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+fn CompareStr(s: String) -> i32 {
+  // CHECK:STDERR: SYNTAX ERROR: fail_raw_block_single_line.carbon:[[@LINE+1]]: Invalid block string: Too few lines
+  if (s == #'''raw string literal starting with '''#) {
+    return 0;
+  }
+  return 1;
+}
+
+fn Main() -> i32 {
+  return CompareStr("\"\"raw string literal starting with \"\"");
+}
diff --git a/toolchain/semantics/fuzzer_corpus/299dc67e6adcc047d41fb7c54c8733ae1f5a730f b/toolchain/semantics/fuzzer_corpus/299dc67e6adcc047d41fb7c54c8733ae1f5a730f
new file mode 100644
index 000000000000..ce3030e49b34
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/299dc67e6adcc047d41fb7c54c8733ae1f5a730f
@@ -0,0 +1,13 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 1
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  var x: i32;
+  return 1;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/2c68b43d8a3accf3dffde64ee1346170c321cf8a b/toolchain/semantics/fuzzer_corpus/2c68b43d8a3accf3dffde64ee1346170c321cf8a
new file mode 100644
index 000000000000..085ce2153955
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/2c68b43d8a3accf3dffde64ee1346170c321cf8a
@@ -0,0 +1,13 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  // CHECK:STDERR: RUNTIME ERROR: fail_div_by_zero.carbon:[[@LINE+1]]: division by zero
+  var a: auto = 5 / 0;
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/2c8bd9d51c37b6e039d31465180dcd971e372a33 b/toolchain/semantics/fuzzer_corpus/2c8bd9d51c37b6e039d31465180dcd971e372a33
new file mode 100644
index 000000000000..34d71a7caeea
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/2c8bd9d51c37b6e039d31465180dcd971e372a33
@@ -0,0 +1,20 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+fn ReturnIndirectly[T:! type](direct: bool, x: T) -> type {
+  if (direct) {
+    return T;
+  } else {
+    return ReturnIndirectly(true, x);
+  }
+}
+
+fn Main() -> ReturnIndirectly(false, 0) {
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/2cd24a29608035201b59f604b1c06ffd230df13e b/toolchain/semantics/fuzzer_corpus/2cd24a29608035201b59f604b1c06ffd230df13e
new file mode 100644
index 000000000000..068365f7c1e1
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/2cd24a29608035201b59f604b1c06ffd230df13e
@@ -0,0 +1,18 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 1
+
+package ExplorerTest api;
+class A(T:! type) {
+  var v: T;
+}
+fn F(T:! type, x: T) -> T {
+  var v: A(T) = {.v = x};
+  return v.v;
+}
+fn Main() -> i32 {
+  return F(i32, 1);
+}
diff --git a/toolchain/semantics/fuzzer_corpus/2e7f4e15df56d8a05046d80c7a7ce01e6cb6779b b/toolchain/semantics/fuzzer_corpus/2e7f4e15df56d8a05046d80c7a7ce01e6cb6779b
new file mode 100644
index 000000000000..7cae1fe42d40
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/2e7f4e15df56d8a05046d80c7a7ce01e6cb6779b
@@ -0,0 +1,75 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: MemberF.F
+// CHECK:STDOUT: ImplF.(HasF.F)
+// CHECK:STDOUT: BothFs.(HasF.F)
+// CHECK:STDOUT: BothFs.F
+// CHECK:STDOUT: BothFs.F
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+choice ImplKind {
+  Checked,
+  ConstrainedTemplate,
+  UnconstrainedTemplate
+}
+
+interface CallF(K:! ImplKind) {
+  fn DoIt[self: Self]();
+}
+
+interface HasF {
+  fn F[self: Self]();
+}
+
+impl forall [T:! HasF] T as CallF(ImplKind.Checked) {
+  fn DoIt[self: Self]() { self.F(); }
+}
+
+impl forall [template T:! HasF] T as CallF(ImplKind.ConstrainedTemplate) {
+  fn DoIt[self: Self]() { self.F(); }
+}
+
+impl forall [template T:! type] T as CallF(ImplKind.UnconstrainedTemplate) {
+  fn DoIt[self: Self]() { self.F(); }
+}
+
+class MemberF {
+  fn F[self: Self]() { Print("MemberF.F"); }
+}
+
+class ImplF {}
+impl ImplF as HasF {
+  fn F[self: Self]() { Print("ImplF.(HasF.F)"); }
+}
+
+class BothFs {
+  fn F[self: Self]() { Print("BothFs.F"); }
+}
+impl BothFs as HasF {
+  fn F[self: Self]() { Print("BothFs.(HasF.F)"); }
+}
+
+fn Main() -> i32 {
+  var mem: MemberF = {};
+  var imp: ImplF = {};
+  var both: BothFs = {};
+
+  mem.(CallF(ImplKind.UnconstrainedTemplate).DoIt)();
+
+  imp.(CallF(ImplKind.Checked).DoIt)();
+  // TODO: Should be valid, but currently fails during instantiation.
+  //imp.(CallF(ImplKind.ConstrainedTemplate).DoIt)();
+
+  both.(CallF(ImplKind.Checked).DoIt)();
+  // TODO: Should be rejected, but currently incorrectly accepted.
+  // This line can be deleted once it starts failing; we test that this is
+  // rejected in fail_name_lookup.carbon.
+  both.(CallF(ImplKind.ConstrainedTemplate).DoIt)();
+  both.(CallF(ImplKind.UnconstrainedTemplate).DoIt)();
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/2f13aa997ff8ff9e53fa3e0d38fd27ff214319d9 b/toolchain/semantics/fuzzer_corpus/2f13aa997ff8ff9e53fa3e0d38fd27ff214319d9
new file mode 100644
index 000000000000..5535e4c6a276
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/2f13aa997ff8ff9e53fa3e0d38fd27ff214319d9
@@ -0,0 +1,18 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  if (0 == 1) {
+    return 1;
+  } else if (0 == 0) {
+    return 0;
+  }
+
+  return 1;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/2f1e5bc51212e421a902e31273599bea2ede8c62 b/toolchain/semantics/fuzzer_corpus/2f1e5bc51212e421a902e31273599bea2ede8c62
new file mode 100644
index 000000000000..0d8151d4d252
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/2f1e5bc51212e421a902e31273599bea2ede8c62
@@ -0,0 +1,16 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 1
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  var n: i32 = 0;
+  match (n) {
+    case 1 => { return 0; }
+  }
+  return 1;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/2fb9acfa600396821f70f238b1c20f95e40a25b9 b/toolchain/semantics/fuzzer_corpus/2fb9acfa600396821f70f238b1c20f95e40a25b9
new file mode 100644
index 000000000000..b4ac5bc4c3c2
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/2fb9acfa600396821f70f238b1c20f95e40a25b9
@@ -0,0 +1,21 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+interface I {}
+impl i32 as I {}
+
+fn F(A:! i32, B:! i32, C:! i32, D:! i32, E:! i32,
+     T:! I where A == B and C == D and C == E and B == D) {
+  // CHECK:STDERR: COMPILATION ERROR: fail_combine_equality.carbon:[[@LINE+1]]: member access, F not in interface I where T impls interface I and A == B and C == D and C == E and B == D
+  T.F();
+}
+
+fn Main() -> i32 {
+  F(1, 1, 1, 1, 1, i32);
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/30243c0f830ca810070c9dc52e11026d673fd3de b/toolchain/semantics/fuzzer_corpus/30243c0f830ca810070c9dc52e11026d673fd3de
new file mode 100644
index 000000000000..1163222aaeb2
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/30243c0f830ca810070c9dc52e11026d673fd3de
@@ -0,0 +1,19 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 6
+
+package ExplorerTest api;
+
+namespace N;
+
+fn OuterI32() -> type { return i32; }
+fn One() -> i32 { return 1; }
+
+fn N.I32() -> type { return i32; }
+fn N.Five() -> I32() { return 5; }
+fn N.Six() -> OuterI32() { return Five() + One(); }
+
+fn Main() -> i32 { return N.Six(); }
diff --git a/toolchain/semantics/fuzzer_corpus/3079f1de829d6dad1caef247d2d2965ab0a2233f b/toolchain/semantics/fuzzer_corpus/3079f1de829d6dad1caef247d2d2965ab0a2233f
new file mode 100644
index 000000000000..a5b2054edaf7
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/3079f1de829d6dad1caef247d2d2965ab0a2233f
@@ -0,0 +1,30 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+__mixin M1 {
+  fn Scale10[self: Self](x:i32) -> i32{
+     return x * 10;
+  }
+}
+
+__mixin M2 {
+  __mix M1;
+  fn Square[self: Self](x:i32) -> i32{
+    return x * x;
+  }
+}
+
+class C {
+  __mix M2;
+}
+
+fn Main() -> i32 {
+  var c: C = {};
+  return c.Square(11) - c.Scale10(10) - 21;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/307b97c6b60b4f05d53a656201995e1fb502af02 b/toolchain/semantics/fuzzer_corpus/307b97c6b60b4f05d53a656201995e1fb502af02
new file mode 100644
index 000000000000..e488093f738e
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/307b97c6b60b4f05d53a656201995e1fb502af02
@@ -0,0 +1,17 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+class C {
+  // CHECK:STDERR: COMPILATION ERROR: fail_use_before_typecheck.carbon:[[@LINE+1]]: incomplete type `class C` used in member access
+  var n: if not C.WrapInStruct() then i32 else {.n: i32};
+  fn WrapInStruct() -> bool { return true; }
+}
+
+fn Main() -> i32 {
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/3161b5f7fb9fc09982d28e2255f3d2ae27fc5ce1 b/toolchain/semantics/fuzzer_corpus/3161b5f7fb9fc09982d28e2255f3d2ae27fc5ce1
new file mode 100644
index 000000000000..9ce6d82be110
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/3161b5f7fb9fc09982d28e2255f3d2ae27fc5ce1
@@ -0,0 +1,15 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 1
+
+package ExplorerTest api;
+
+var x: i32;
+
+fn Main() -> i32 {
+  x = 1;
+  return x;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/31e0e6f587bdffffc37922b7b3f771680232bb31 b/toolchain/semantics/fuzzer_corpus/31e0e6f587bdffffc37922b7b3f771680232bb31
new file mode 100644
index 000000000000..206753a770b7
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/31e0e6f587bdffffc37922b7b3f771680232bb31
@@ -0,0 +1,13 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  var x: [[i32; 3]; 2] = ((0, 1, 2), (3, 4, 5));
+  return x[1][2] - 5;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/31ef33085e7420998380c7dd66d8529ad975f7a4 b/toolchain/semantics/fuzzer_corpus/31ef33085e7420998380c7dd66d8529ad975f7a4
new file mode 100644
index 000000000000..a61c420989ab
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/31ef33085e7420998380c7dd66d8529ad975f7a4
@@ -0,0 +1,56 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: bool: 1
+// CHECK:STDOUT: bool: 1
+// CHECK:STDOUT: bool: 1
+// CHECK:STDOUT: bool: 1
+// CHECK:STDOUT: bool: 1
+// CHECK:STDOUT: bool: 1
+// CHECK:STDOUT: bool: 1
+// CHECK:STDOUT: bool: 1
+// CHECK:STDOUT: string: 1
+// CHECK:STDOUT: string: 1
+// CHECK:STDOUT: string: 1
+// CHECK:STDOUT: string: 1
+// CHECK:STDOUT: string: 1
+// CHECK:STDOUT: string: 1
+// CHECK:STDOUT: string: 1
+// CHECK:STDOUT: string: 1
+// CHECK:STDOUT: int: 1
+// CHECK:STDOUT: int: 1
+// CHECK:STDOUT: int: 1
+// CHECK:STDOUT: int: 1
+// CHECK:STDOUT: int: 1
+// CHECK:STDOUT: int: 1
+// CHECK:STDOUT: int: 1
+// CHECK:STDOUT: int: 1
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+fn CompareEqualValues[T:! EqWith(.Self)](format: String, a: T, b: T) {
+  Print(format, if a == b then 1 else 0);
+  Print(format, if a != b then 0 else 1);
+}
+
+fn CompareDifferentValues[U:! EqWith(.Self)](format: String, a: U, b: U) {
+  Print(format, if a == b then 0 else 1);
+  Print(format, if a != b then 1 else 0);
+}
+
+fn CompareAll[V:! EqWith(.Self)](format: String, a: V, b: V) {
+  CompareEqualValues(format, a, a);
+  CompareEqualValues(format, b, b);
+  CompareDifferentValues(format, a, b);
+  CompareDifferentValues(format, b, a);
+}
+
+fn Main() -> i32 {
+  CompareAll("bool: {0}", false, true);
+  CompareAll("string: {0}", "hello", "world");
+  CompareAll("int: {0}", 1, 2);
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/3246530de7e46a174acd24fd87d38695fd5e36c9 b/toolchain/semantics/fuzzer_corpus/3246530de7e46a174acd24fd87d38695fd5e36c9
new file mode 100644
index 000000000000..f15dfd9788e7
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/3246530de7e46a174acd24fd87d38695fd5e36c9
@@ -0,0 +1,43 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: DESTRUCTOR A 1
+// CHECK:STDOUT: DESTRUCTOR B 2
+// CHECK:STDOUT: DESTRUCTOR A 3
+// CHECK:STDOUT: DESTRUCTOR A 4
+// CHECK:STDOUT: DESTRUCTOR A 5
+// CHECK:STDOUT: result: 1
+
+package ExplorerTest api;
+
+class A{
+    destructor[self: Self]{
+        Print("DESTRUCTOR A {0}",self.n);
+    }
+    fn Create(x: i32) -> A{
+        return {.n = x};
+    }
+    var n: i32;
+}
+
+class B{
+    destructor[self: Self]{
+        Print("DESTRUCTOR B {0}",self.n);
+    }
+    fn Create(x: i32) -> B{
+       return {.n = x, .a1 = A.Create(4),.a2 = A.Create(3) };
+    }
+    var a1: A;
+    var n: i32;
+    var a2: A;
+}
+
+
+fn Main() -> i32 {
+  var a: A = A.Create(5);
+  var b: B = B.Create(2);
+  var c: A = A.Create(1);
+  return 1;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/326f616ba0e75fe934290f59801ffeecb97fad51 b/toolchain/semantics/fuzzer_corpus/326f616ba0e75fe934290f59801ffeecb97fad51
new file mode 100644
index 000000000000..37998dabe8b9
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/326f616ba0e75fe934290f59801ffeecb97fad51
@@ -0,0 +1,17 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+class A {
+  fn F[self: Self]() -> i32;
+}
+
+fn Main() -> i32 {
+  var a: A = {};
+  // CHECK:STDERR: RUNTIME ERROR: fail_call_undefined_method.carbon:[[@LINE+1]]: attempt to call function `F` that has not been defined
+  return a.F();
+}
diff --git a/toolchain/semantics/fuzzer_corpus/328768bbd4cee309586c935aa27bedf19202ef39 b/toolchain/semantics/fuzzer_corpus/328768bbd4cee309586c935aa27bedf19202ef39
new file mode 100644
index 000000000000..92caffe5e46a
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/328768bbd4cee309586c935aa27bedf19202ef39
@@ -0,0 +1,13 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  // CHECK:STDERR: SYNTAX ERROR: fail_octal.carbon:[[@LINE+1]]: Invalid escaping in string: "str\01"
+  Print("str\01");
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/32ab1efa550be4f04cc3d07bf05a8804d09b754b b/toolchain/semantics/fuzzer_corpus/32ab1efa550be4f04cc3d07bf05a8804d09b754b
new file mode 100644
index 000000000000..95a4fd8449ad
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/32ab1efa550be4f04cc3d07bf05a8804d09b754b
@@ -0,0 +1,16 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  var (x: i32, y: i32);
+  // CHECK:STDERR: COMPILATION ERROR: fail_while_cond.carbon:[[@LINE+1]]: use of uninitialized variable x
+  while (x == 0) {
+    y = 1;
+  }
+  return 1;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/33346b680817ff4c2a003195a0a712daee297f8f b/toolchain/semantics/fuzzer_corpus/33346b680817ff4c2a003195a0a712daee297f8f
new file mode 100644
index 000000000000..1f29b4a8300f
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/33346b680817ff4c2a003195a0a712daee297f8f
@@ -0,0 +1,15 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package Foo api;
+fn F[self: i32]() {}
+fn Main() -> i32 {
+  // TODO: It's unclear whether this is valid per the current rules. See
+  // https://github.com/carbon-language/carbon-lang/pull/1122
+  // CHECK:STDERR: COMPILATION ERROR: fail_qualified_non_member.carbon:[[@LINE+1]]: expected name of instance member or interface member in compound member access, found fn [self: i32]() -> ()
+  42.(F)();
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/347494c3bd46b47f162b4abe214f5f71881dd126 b/toolchain/semantics/fuzzer_corpus/347494c3bd46b47f162b4abe214f5f71881dd126
new file mode 100644
index 000000000000..75fbf9f76f57
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/347494c3bd46b47f162b4abe214f5f71881dd126
@@ -0,0 +1,22 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+class Point {
+  fn Origin() -> Point {
+    return {.x = 0, .y = 0};
+  }
+
+  var x: i32;
+  var y: i32;
+}
+
+fn Main() -> i32 {
+  var p: Point = Point.Origin();
+  return p.x;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/34d5a979143e2dac42a721445d89d3681f13f4cd b/toolchain/semantics/fuzzer_corpus/34d5a979143e2dac42a721445d89d3681f13f4cd
new file mode 100644
index 000000000000..b9f2a8f7a34c
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/34d5a979143e2dac42a721445d89d3681f13f4cd
@@ -0,0 +1,25 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+interface Container {
+  let Element:! type;
+  fn Front[self: Self]() -> Element;
+}
+
+fn A[T:! Container where .Element = i32](x: T) -> T.Element {
+  return x.Front();
+}
+
+fn B[T:! Container](x: T) -> i32 {
+  // CHECK:STDERR: COMPILATION ERROR: fail_missing_rewrite.carbon:[[@LINE+1]]: constraint requires that (T).(Container.Element) (with value (T).(Container.Element)) == i32, which is not known to be true
+  return A(x);
+}
+
+fn Main() -> i32 {
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/34ff001dd827e172826dd1a040df88b4f7d15a01 b/toolchain/semantics/fuzzer_corpus/34ff001dd827e172826dd1a040df88b4f7d15a01
new file mode 100644
index 000000000000..b8da28ebed8f
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/34ff001dd827e172826dd1a040df88b4f7d15a01
@@ -0,0 +1,52 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: Initialize c1 from initializing expression (returned var)
+// CHECK:STDOUT: Before nested init
+// CHECK:STDOUT: 0: Heap{}, 1: !Uninit<class C>
+// CHECK:STDOUT: Nested call return
+// CHECK:STDOUT: 0: Heap{}, 1: C{}
+// CHECK:STDOUT: First call return
+// CHECK:STDOUT: 0: Heap{}, 1: C{}
+// CHECK:STDOUT: Declaration scope
+// CHECK:STDOUT: 0: Heap{}, 1: C{}
+// CHECK:STDOUT: c destroyed
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+class C {
+  destructor[self: Self] {
+    Print("c destroyed");
+  }
+}
+
+fn CallWithReturnedVar2() -> C {
+  Print("Before nested init");
+  heap.PrintAllocs();
+  returned var c: C = {};
+  Print("Nested call return");
+  heap.PrintAllocs();
+  return var;
+}
+
+fn CallWithReturnedVar() -> C {
+  returned var c: C = CallWithReturnedVar2();
+  Print("First call return");
+  heap.PrintAllocs();
+  return var;
+}
+
+fn FromInitializingExpression_ReturnedVar() {
+  Print("Initialize c1 from initializing expression (returned var)");
+  let c: C = CallWithReturnedVar();
+  Print("Declaration scope");
+  heap.PrintAllocs();
+}
+
+fn Main() -> i32 {
+  FromInitializingExpression_ReturnedVar();
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/35538f6224efb57c9edb0fa3da9f3679a1a1ceed b/toolchain/semantics/fuzzer_corpus/35538f6224efb57c9edb0fa3da9f3679a1a1ceed
new file mode 100644
index 000000000000..976faf397261
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/35538f6224efb57c9edb0fa3da9f3679a1a1ceed
@@ -0,0 +1,27 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: 6
+// CHECK:STDOUT: 3
+// CHECK:STDOUT: 1
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+class A { var n: i32; }
+
+impl A as DivWith(i32) where .Result = A {
+  fn Op[self: Self](rhs: i32) -> A { return {.n = self.n / rhs}; }
+}
+
+fn Main() -> i32 {
+  var a: A = {.n = 19};
+  a = a / 3;
+  Print("{0}", a.n);
+  a /= 2;
+  Print("{0}", a.n);
+  Print("{0}", (a / 2).n);
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/36717d4dda9919479b60d7150b62df44499a51fd b/toolchain/semantics/fuzzer_corpus/36717d4dda9919479b60d7150b62df44499a51fd
new file mode 100644
index 000000000000..8cc3aafe567c
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/36717d4dda9919479b60d7150b62df44499a51fd
@@ -0,0 +1,32 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: DESTRUCTOR A 1
+// CHECK:STDOUT: DESTRUCTOR A 2
+// CHECK:STDOUT: DESTRUCTOR A 3
+// CHECK:STDOUT: DESTRUCTOR A 1
+// CHECK:STDOUT: DESTRUCTOR A 2
+// CHECK:STDOUT: DESTRUCTOR A 3
+// CHECK:STDOUT: result: 1
+
+package ExplorerTest api;
+
+class A{
+    destructor[self: Self]{
+        Print("DESTRUCTOR A {0}",self.n);
+    }
+    var n: i32;
+}
+
+fn Main() -> i32 {
+  var i: i32 = 0;
+  while( i < 2){
+    var a: A = {.n = 3};
+    var b: A = {.n = 2};
+    var c: A = {.n = 1};
+    i = i + 1;
+  }
+  return 1;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/36b957f732d3b3eb30b528c109683f3ff3e738f9 b/toolchain/semantics/fuzzer_corpus/36b957f732d3b3eb30b528c109683f3ff3e738f9
new file mode 100644
index 000000000000..409b82628c8a
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/36b957f732d3b3eb30b528c109683f3ff3e738f9
@@ -0,0 +1,23 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: 3
+// CHECK:STDOUT: 4
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  var a: (i32, i32) = (1, 2);
+  var p: (i32, i32)* = &a;
+
+  a[0] = 3;
+  Print("{0}", (*p)[0]);
+
+  (*p)[1] = 4;
+  Print("{0}", a[1]);
+
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/374e96ca0653e9f238dad0aa53e6d8243460302e b/toolchain/semantics/fuzzer_corpus/374e96ca0653e9f238dad0aa53e6d8243460302e
new file mode 100644
index 000000000000..92c34d605e83
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/374e96ca0653e9f238dad0aa53e6d8243460302e
@@ -0,0 +1,16 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+fn Main() -> i32{
+  var x: Optional(String) = Optional(String).CreateEmpty();
+  if(x.HasValue()){
+    return -1;
+  }
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/3974726c6015a615360574cb1221200e183175c2 b/toolchain/semantics/fuzzer_corpus/3974726c6015a615360574cb1221200e183175c2
new file mode 100644
index 000000000000..13f0b6f496c7
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/3974726c6015a615360574cb1221200e183175c2
@@ -0,0 +1,17 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 12
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  var cond: if true then bool else i32 = true;
+  if (if cond then true else false) {}
+  while (if cond then false else true) {}
+  return if if cond then true or false else false and true
+         then if not cond then 1 + 2 else 3 * 4
+         else if not cond then 5 + 6 else 7 * 8;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/3a4ba37f94cf21edb7969ed61c1fea9a0f3eb56c b/toolchain/semantics/fuzzer_corpus/3a4ba37f94cf21edb7969ed61c1fea9a0f3eb56c
new file mode 100644
index 000000000000..241384329919
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/3a4ba37f94cf21edb7969ed61c1fea9a0f3eb56c
@@ -0,0 +1,15 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  var p: i32* = __intrinsic_new(0);
+  var y: i32 = *p;
+  __intrinsic_delete(p);
+  return y;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/3bddb2be6780b792248656a086347171ecca2f1d b/toolchain/semantics/fuzzer_corpus/3bddb2be6780b792248656a086347171ecca2f1d
new file mode 100644
index 000000000000..ccc4905c53c4
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/3bddb2be6780b792248656a086347171ecca2f1d
@@ -0,0 +1,66 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: Allocate D
+// CHECK:STDOUT: DESTRUCTOR B
+// CHECK:STDOUT: DESTRUCTOR A
+// CHECK:STDOUT: DESTRUCTOR D
+// CHECK:STDOUT: DESTRUCTOR C
+// CHECK:STDOUT: Delete B from A*
+// CHECK:STDOUT: DESTRUCTOR B
+// CHECK:STDOUT: DESTRUCTOR A
+// CHECK:STDOUT: Delete D from C*
+// CHECK:STDOUT: DESTRUCTOR D
+// CHECK:STDOUT: DESTRUCTOR C
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+base class A {
+  virtual destructor[self: Self] {
+    Print("DESTRUCTOR A");
+  }
+}
+
+class B {
+  extend base: A;
+  fn Create() -> Self{
+    return {.base={}};
+  }
+  impl destructor[self: Self] {
+    Print("DESTRUCTOR B");
+  }
+}
+
+base class C {
+  virtual destructor[self: Self] {
+    Print("DESTRUCTOR C");
+  }
+}
+
+class D {
+  extend base: C;
+  fn Create() -> Self{
+    return {.base={}, .d_pa=heap.New(B.Create())};
+  }
+  impl destructor[self: Self] {
+    Print("DESTRUCTOR D");
+  }
+  var d_pa: A*;
+}
+
+fn Main() -> i32 {
+  Print("Allocate D");
+  var pd: D* = heap.New(D.Create());
+  var pc: C* = pd;
+
+  Print("Delete B from A*");
+  heap.Delete(pd->d_pa);
+
+  Print("Delete D from C*");
+  heap.Delete(pc);
+
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/3def80179ffa13dd5984676ace7c0d8e9cac2031 b/toolchain/semantics/fuzzer_corpus/3def80179ffa13dd5984676ace7c0d8e9cac2031
new file mode 100644
index 000000000000..206fba708b83
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/3def80179ffa13dd5984676ace7c0d8e9cac2031
@@ -0,0 +1,26 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+class Point(T:! type) {
+  fn Origin(zero: T) -> Point(T) {
+    return {.x = zero, .y = zero};
+  }
+
+  fn GetX[self: Point(T)]() -> T {
+    return self.x;
+  }
+
+  var x: T;
+  var y: T;
+}
+
+fn Main() -> i32 {
+  var p: Point(i32) = Point(i32).Origin(0);
+  return p.GetX();
+}
diff --git a/toolchain/semantics/fuzzer_corpus/3e51c009c54026d5e2cbbfe253b38765d4e71c63 b/toolchain/semantics/fuzzer_corpus/3e51c009c54026d5e2cbbfe253b38765d4e71c63
new file mode 100644
index 000000000000..47d14bc8c5a0
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/3e51c009c54026d5e2cbbfe253b38765d4e71c63
@@ -0,0 +1,23 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+// Check that even generic parameters are looked up in the namespace of an
+// entity.
+namespace N;
+
+interface N.Interface {}
+
+class N.A(T:! Interface) {}
+interface N.B(T:! Interface) {}
+constraint N.C(T:! Interface) {}
+__mixin N.D(T:! Interface) {}
+choice N.E(T:! Interface) {}
+fn N.F[T:! Interface](a: A(T)) {}
+
+fn Main() -> i32 { return 0; }
diff --git a/toolchain/semantics/fuzzer_corpus/3fa85a4f6a6e080e9c47b7de21848308a54fb12d b/toolchain/semantics/fuzzer_corpus/3fa85a4f6a6e080e9c47b7de21848308a54fb12d
new file mode 100644
index 000000000000..4bac78fe11bf
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/3fa85a4f6a6e080e9c47b7de21848308a54fb12d
@@ -0,0 +1,13 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  // CHECK:STDERR: RUNTIME ERROR: fail_overflow_multiply.carbon:[[@LINE+1]]: integer overflow
+  var a: auto = 1000000000 * 1000000000;
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/40ec85973059ea2eb5ad4495a0e72412427eb429 b/toolchain/semantics/fuzzer_corpus/40ec85973059ea2eb5ad4495a0e72412427eb429
new file mode 100644
index 000000000000..5967d6f82ae0
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/40ec85973059ea2eb5ad4495a0e72412427eb429
@@ -0,0 +1,19 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 5
+
+package ExplorerTest api;
+
+class A { var n: i32; }
+
+impl A as ImplicitAs(i32) {
+  fn Convert[self: Self]() -> i32 { return self.n; }
+}
+
+fn Main() -> i32 {
+  var a: A = {.n = 5};
+  return a as i32;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/410e360fb25137ae34bb10ba8f43389970784769 b/toolchain/semantics/fuzzer_corpus/410e360fb25137ae34bb10ba8f43389970784769
new file mode 100644
index 000000000000..5f3377aa8111
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/410e360fb25137ae34bb10ba8f43389970784769
@@ -0,0 +1,34 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 1234
+
+package ExplorerTest api;
+
+interface A {
+  fn F() -> i32;
+}
+interface B {
+  fn F() -> i32;
+  fn G() -> i32;
+}
+interface C(T:! type) {
+  fn H() -> T;
+}
+
+impl i32 as A {
+  fn F() -> i32 { return 1; }
+}
+
+impl i32 as B & C(i32) where .Self impls A {
+  fn F() -> i32 { return 2; }
+  fn G() -> i32 { return 3; }
+  fn H() -> i32 { return 4; }
+}
+
+fn Main() -> i32 {
+  let n: i32 = 0;
+  return n.(A.F)() * 1000 + n.(B.F)() * 100 + n.(B.G)() * 10 + n.(C(i32).H)();
+}
diff --git a/toolchain/semantics/fuzzer_corpus/431046fc9aad6d960aac0e19b676292fb66cba26 b/toolchain/semantics/fuzzer_corpus/431046fc9aad6d960aac0e19b676292fb66cba26
new file mode 100644
index 000000000000..1e96daef965f
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/431046fc9aad6d960aac0e19b676292fb66cba26
@@ -0,0 +1,34 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+// TODO: Should this work?
+
+package ExplorerTest api;
+
+interface Vector {
+  let Dim:! i32;
+}
+impl (i32, i32, i32) as Vector where .Dim = 3 {}
+
+class Point(Scalar:! type, Dim:! i32) {}
+
+fn F[Scalar:! type, V:! Vector where .Dim == 3](p: Point(Scalar, V.Dim), v: V) {}
+
+fn G[Scalar:! type](p: Point(Scalar, 3)) {}
+fn H[V:! Vector where .Dim == 3](v: V) {
+  var p: Point(i32, V.Dim) = {};
+  // CHECK:STDERR: COMPILATION ERROR: fail_match_in_deduction.carbon:[[@LINE+1]]: mismatch in non-deduced values, `(V).(Vector.Dim)` != `3`
+  G(p);
+}
+
+fn Main() -> i32 {
+  var p: Point(i32, 3) = {};
+  // Deduce Point(Scalar, V.Dim) from Point(i32, 3).
+  F(p, (0, 0, 0));
+  // Deduce Point(Scalar, 3) from Point(i32, V.Dim).
+  H((0, 0, 0));
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/4354d5620d966751cc545a5e9a7c55d263875c66 b/toolchain/semantics/fuzzer_corpus/4354d5620d966751cc545a5e9a7c55d263875c66
new file mode 100644
index 000000000000..4b77def8ecdb
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/4354d5620d966751cc545a5e9a7c55d263875c66
@@ -0,0 +1,17 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+fn F() {
+  return;
+}
+
+fn Main() -> i32 {
+  F();
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/4367b235dfdad01ab5652abfe5052b5b1a410d82 b/toolchain/semantics/fuzzer_corpus/4367b235dfdad01ab5652abfe5052b5b1a410d82
new file mode 100644
index 000000000000..4cdb1378da07
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/4367b235dfdad01ab5652abfe5052b5b1a410d82
@@ -0,0 +1,27 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: 10
+// CHECK:STDOUT: 30
+// CHECK:STDOUT: 210
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+class A { var n: i32; }
+
+impl A as MulWith(i32) where .Result = A {
+  fn Op[self: Self](rhs: i32) -> A { return {.n = self.n * rhs}; }
+}
+
+fn Main() -> i32 {
+  var a: A = {.n = 5};
+  a = a * 2;
+  Print("{0}", a.n);
+  a *= 3;
+  Print("{0}", a.n);
+  Print("{0}", (a * 7).n);
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/43921c8fea3dd42753e50ac91c5d83d87e1c3bea b/toolchain/semantics/fuzzer_corpus/43921c8fea3dd42753e50ac91c5d83d87e1c3bea
new file mode 100644
index 000000000000..91ca3a7a3aaf
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/43921c8fea3dd42753e50ac91c5d83d87e1c3bea
@@ -0,0 +1,17 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+class C {
+  // CHECK:STDERR: COMPILATION ERROR: fail_circular_inheritance.carbon:[[@LINE+4]]: could not find `class C {
+  // CHECK:STDERR: extend base: C;
+  // CHECK:STDERR: }
+  // CHECK:STDERR: `
+  extend base: C;
+}
+
+fn Main() -> i32 { return 0; }
diff --git a/toolchain/semantics/fuzzer_corpus/4487e8bd672c03926d372d25aa108d6fa909c11a b/toolchain/semantics/fuzzer_corpus/4487e8bd672c03926d372d25aa108d6fa909c11a
new file mode 100644
index 000000000000..91325ed4b3c8
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/4487e8bd672c03926d372d25aa108d6fa909c11a
@@ -0,0 +1,41 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 3
+
+package ExplorerTest api;
+
+class Cell(T:! type) {
+  fn Create(x: T) -> Cell(T) { return { .data = x }; }
+
+  fn Get[self: Self]() -> T {
+    return self.data;
+  }
+  fn Put[addr self: Self*](x: T) {
+    (*self).data = x;
+  }
+  fn Update[addr self: Self*, U:! ImplicitAs(T)](x: U) {
+    (*self).data = x;
+  }
+  fn CreateOther[self: Self, U:! type](x: U) -> Cell(U) {
+    return {.data = x};
+  }
+  var data: T;
+}
+
+class Integer {
+  var int: i32;
+}
+
+fn Main() -> i32 {
+  var i: Integer = {.int = 1};
+  var c: Cell(Integer) = Cell(Integer).Create(i); // c contains 1
+  i = {.int = 2};
+  var j: Integer = c.Get(); // j == 1
+  c.Put(i);    // c contains 2
+  c.Update(j); // c contains 1
+  var d: Cell(Integer) = c.CreateOther(i); // d contains 2
+  return c.data.int + d.data.int;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/44b9bb4873ea7ed7eeddd3cd5af4bbb71507e31d b/toolchain/semantics/fuzzer_corpus/44b9bb4873ea7ed7eeddd3cd5af4bbb71507e31d
new file mode 100644
index 000000000000..545436a5286d
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/44b9bb4873ea7ed7eeddd3cd5af4bbb71507e31d
@@ -0,0 +1,30 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+interface X(T:! type) {}
+
+interface Y(T:! type) {
+    let M:! X(T);
+}
+
+interface Z {
+  // The `i32 impls X(.Self)` constraint is indirectly required by
+  // specifying that `.M = i32`.
+  let N:! Y(.Self) where i32 impls X(.Self) and .M = i32;
+}
+
+impl i32 as X(i32) {}
+impl i32 as Y(i32) where .M = i32 {}
+impl i32 as Z where .N = i32 {}
+
+fn F[A:! Z](a: A) -> A { return a; }
+
+fn Main() -> i32 {
+  return F(0);
+}
diff --git a/toolchain/semantics/fuzzer_corpus/45254859420f71824fe5123a1ce3fd71e25bc505 b/toolchain/semantics/fuzzer_corpus/45254859420f71824fe5123a1ce3fd71e25bc505
new file mode 100644
index 000000000000..35f46a5c49af
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/45254859420f71824fe5123a1ce3fd71e25bc505
@@ -0,0 +1,17 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+class A {
+  class B {}
+  alias C = B;
+}
+
+fn Main() -> i32 {
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/45579d56ffeffc9eb8926dc0cbcf5e86f34762a9 b/toolchain/semantics/fuzzer_corpus/45579d56ffeffc9eb8926dc0cbcf5e86f34762a9
new file mode 100644
index 000000000000..a655dd2b8f95
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/45579d56ffeffc9eb8926dc0cbcf5e86f34762a9
@@ -0,0 +1,48 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+interface Number {
+  fn Zero() -> Self;
+  fn Add[self: Self](other: Self) -> Self;
+}
+
+class Point(T:! Number) {
+  var x: T;
+  var y: T;
+}
+
+impl i32 as Number {
+  fn Zero() -> i32 { return 0; }
+  fn Add[self: i32](other: i32) -> i32 { return self + other; }
+}
+
+impl forall [U:! Number] Point(U) as Number {
+  fn Zero() -> Point(U) { return {.x = U.Zero(), .y = U.Zero() }; }
+  fn Add[self: Point(U)](other: Point(U)) -> Point(U) {
+    return {.x = self.x.Add(other.x), .y = self.y.Add(other.y)};
+  }
+}
+
+fn Sum[E:! Number](x: E, y: E) -> E {
+  var total: E = E.Zero();
+  total = total.Add(x);
+  total = total.Add(y);
+  return total;
+}
+
+fn SumPoints[E:! Number](p: Point(E), q: Point(E)) -> Point(E) {
+  return Sum(p, q);
+}
+
+fn Main() -> i32 {
+  var p: Point(i32) = {.x = 1, .y = 2};
+  var q: Point(i32) = {.x = 4, .y = 3};
+  var r: Point(i32) = SumPoints(p, q);
+  return r.x - r.y;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/4577557849cfb38a618ee2da85894b9295c24506 b/toolchain/semantics/fuzzer_corpus/4577557849cfb38a618ee2da85894b9295c24506
new file mode 100644
index 000000000000..1ebf69c056d6
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/4577557849cfb38a618ee2da85894b9295c24506
@@ -0,0 +1,20 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+class Point {
+  var x: i32;
+  var y: i32;
+}
+
+fn Main() -> i32 {
+  var p1: Point = {.x = 1, .y = 2};
+  var p2: auto = p1;
+  p2.x = 3;
+  return p1.x - 1;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/45de89d2347b547989589fb86ada1b4af7f9d556 b/toolchain/semantics/fuzzer_corpus/45de89d2347b547989589fb86ada1b4af7f9d556
new file mode 100644
index 000000000000..6442b1afc6ea
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/45de89d2347b547989589fb86ada1b4af7f9d556
@@ -0,0 +1,16 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+fn f(x: i32) -> i32 {
+  return x - 1;
+}
+
+fn Main() -> i32 {
+  return f(1);
+}
diff --git a/toolchain/semantics/fuzzer_corpus/46821819012bbf66e1018171eb9bdd984c20f353 b/toolchain/semantics/fuzzer_corpus/46821819012bbf66e1018171eb9bdd984c20f353
new file mode 100644
index 000000000000..4f52cd2d48b9
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/46821819012bbf66e1018171eb9bdd984c20f353
@@ -0,0 +1,13 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  // CHECK:STDERR: COMPILATION ERROR: fail_unexpected_tuple.carbon:[[@LINE+1]]: didn't expect a tuple
+  var a: (auto,) = 1;
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/46a6da10d752a337c1d2639132658d885a75ee3b b/toolchain/semantics/fuzzer_corpus/46a6da10d752a337c1d2639132658d885a75ee3b
new file mode 100644
index 000000000000..44be53061f50
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/46a6da10d752a337c1d2639132658d885a75ee3b
@@ -0,0 +1,13 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 5
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  let n: i32 = 5;
+  return n as i32;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/46c4faddda6395f30cf8690eb32cd453b255f015 b/toolchain/semantics/fuzzer_corpus/46c4faddda6395f30cf8690eb32cd453b255f015
new file mode 100644
index 000000000000..6a52c1ffc27a
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/46c4faddda6395f30cf8690eb32cd453b255f015
@@ -0,0 +1,17 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+// Test mutation of a global variable.
+
+var zero: i32 = 1;
+
+fn Main() -> i32 {
+  zero = 0;
+  return zero;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/498b32b5cb688f465783e654f788300fd2636a19 b/toolchain/semantics/fuzzer_corpus/498b32b5cb688f465783e654f788300fd2636a19
new file mode 100644
index 000000000000..f00d5ef381f1
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/498b32b5cb688f465783e654f788300fd2636a19
@@ -0,0 +1,48 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: 75
+// CHECK:STDOUT: 100
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+interface Vector {
+  fn Zero() -> Self;
+  fn Add[addr self: Self*](b: Self);
+  fn Scale[addr self: Self*](v: i32);
+}
+
+class Point {
+  var x: i32;
+  var y: i32;
+  extend impl as Vector {
+    fn Zero() -> Self {
+      return {.x = 1, .y = 1};
+    }
+    fn Add[addr self: Self*](b: Self) {
+      (*self).x = (*self).x + b.x;
+      (*self).y = (*self).y + b.y;
+    }
+    fn Scale[addr self: Self*](v: i32) {
+      (*self).x = (*self).x * v;
+      (*self).y = (*self).y * v;
+    }
+  }
+}
+
+fn AddAndScaleGeneric[T:! Vector](p: T*, s: i32) {
+  (*p).Add(T.Zero());
+  (*p).(Vector.Scale)(s);
+  (*p).(T.(Vector.Scale))(s);
+}
+
+fn Main() -> i32 {
+  var a: Point = {.x = 2, .y = 3};
+  AddAndScaleGeneric(&a, 5);
+  Print("{0}", a.x);
+  Print("{0}", a.y);
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/4b82dcd5072f57a2b04077c7e256b32c79410963 b/toolchain/semantics/fuzzer_corpus/4b82dcd5072f57a2b04077c7e256b32c79410963
new file mode 100644
index 000000000000..13be68480348
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/4b82dcd5072f57a2b04077c7e256b32c79410963
@@ -0,0 +1,13 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest impl;
+
+fn Main() -> i32 {
+  // CHECK:STDERR: RUNTIME ERROR: fail_index_empty.carbon:[[@LINE+1]]: Invalid `{}` in `Print: {}`
+  Print("Print: {}");
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/503f8d4fc4bb0e1f1e6cb23cd6b02751684bb242 b/toolchain/semantics/fuzzer_corpus/503f8d4fc4bb0e1f1e6cb23cd6b02751684bb242
new file mode 100644
index 000000000000..c006d8160279
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/503f8d4fc4bb0e1f1e6cb23cd6b02751684bb242
@@ -0,0 +1,27 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+class Point(T:! type) {
+  // Allowed: `Self` means `Point(T)` here.
+  fn Origin(zero: T) -> Self {
+    return {.x = zero, .y = zero};
+  }
+
+  fn GetX[self: Self]() -> T {
+    return self.x;
+  }
+
+  var x: T;
+  var y: T;
+}
+
+fn Main() -> i32 {
+  var p: Point(i32) = Point(i32).Origin(0);
+  return p.GetX();
+}
diff --git a/toolchain/semantics/fuzzer_corpus/5109f6e45e2667ab4a696441b235ab125d247ddb b/toolchain/semantics/fuzzer_corpus/5109f6e45e2667ab4a696441b235ab125d247ddb
new file mode 100644
index 000000000000..e7d023e35bca
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/5109f6e45e2667ab4a696441b235ab125d247ddb
@@ -0,0 +1,31 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 5
+
+package ExplorerTest api;
+
+interface A(T:! type) { let AResult:! type; }
+interface B(T:! type) { let BResult:! A(T); }
+interface I(T:! type) {
+  let X:! B(T);
+  // The constraints introduced by X should be in scope here.
+  let Y:! X.BResult.AResult;
+}
+
+class CA {
+  extend impl as A(i32) where .AResult = i32 {}
+}
+class CB {
+  extend impl as B(i32) where .BResult = CA {}
+}
+class CI {
+  extend impl as I(i32) where .X = CB and .Y = 5 {}
+}
+
+fn Main() -> i32 {
+  var v: CI = {};
+  return v.(I(i32).Y);
+}
diff --git a/toolchain/semantics/fuzzer_corpus/52092056bd9f5f8e5b73e07cf40278c70af4d078 b/toolchain/semantics/fuzzer_corpus/52092056bd9f5f8e5b73e07cf40278c70af4d078
new file mode 100644
index 000000000000..725cd4590cd2
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/52092056bd9f5f8e5b73e07cf40278c70af4d078
@@ -0,0 +1,40 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+interface Vector(Scalar:! type) {
+  fn Zero() -> Self;
+  fn Add[self: Self](b: Self) -> Self;
+  fn Scale[self: Self](v: Scalar) -> Self;
+}
+
+class Point {
+  var x: i32;
+  var y: i32;
+  extend impl as Vector(i32) {
+    fn Zero() -> Point {
+      return {.x = 0, .y = 0};
+    }
+    fn Add[self: Point](b: Point) -> Point {
+      return {.x = self.x + b.x, .y = self.y + b.y};
+    }
+    fn Scale[self: Point](v: i32) -> Point {
+      return {.x = self.x * v, .y = self.y * v};
+    }
+  }
+}
+
+fn AddAndScaleGeneric[T:! type, U:! Vector(T)](a: U, s: T) -> U {
+  return a.Add(U.Zero()).Scale(s);
+}
+
+fn Main() -> i32 {
+  var a: Point = {.x = 2, .y = 1};
+  var p: Point = AddAndScaleGeneric(a, 5);
+  return p.x - 10;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/52d56f074421d8a0d70b7165db6df02000f35359 b/toolchain/semantics/fuzzer_corpus/52d56f074421d8a0d70b7165db6df02000f35359
new file mode 100644
index 000000000000..ee52aa3a9fe9
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/52d56f074421d8a0d70b7165db6df02000f35359
@@ -0,0 +1,42 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 1
+
+package ExplorerTest api;
+
+choice Ints {
+  None,
+  One(i32),
+  Two(i32, i32)
+}
+
+// Test some alternate syntaxes
+choice MoreInts {
+  None(),
+  One(i32),
+  Two(i32, i32),
+}
+
+fn Main() -> i32 {
+  var x: Ints = Ints.None;
+  var y: Ints = Ints.One(42);
+  var z: MoreInts = MoreInts.None();
+  var n: i32 = 0;
+  match (y) {
+    case Ints.None => { n = n + 2; }
+    case Ints.One(x: auto) => { n = x + 1 - 42; }
+    case Ints.Two(a: auto, b: auto) => { n = 2; }
+  }
+  match (x) {
+    case Ints.One(x: auto) => { n = x + 2; }
+    case Ints.None => { n = n - 1; }
+    case Ints.Two(x: auto, y: auto) => { n = 5; }
+  }
+  match (z) {
+    case MoreInts.None() => { ++n; }
+  }
+  return n;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/535b24afa4a13f10f1a4d60a54bc1e1274c2b59b b/toolchain/semantics/fuzzer_corpus/535b24afa4a13f10f1a4d60a54bc1e1274c2b59b
new file mode 100644
index 000000000000..e8fee33057c2
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/535b24afa4a13f10f1a4d60a54bc1e1274c2b59b
@@ -0,0 +1,23 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+class Point {
+  var x: i32;
+  var y: i32;
+}
+
+fn Main() -> i32 {
+  var p: Point;
+  if (1 == 0) {
+    p = {.x = 0, .y = 0};
+  }
+  // CHECK:STDERR: RUNTIME ERROR: fail_store_to_uninitialized_class.carbon:[[@LINE+1]]: undefined behavior: store to subobject of uninitialized value Uninit<Placeholder<p>>
+  p.x = 1;
+  p.y = 2;
+  return p.x;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/53ac25de61ca8f6ef9ed06f4582063bdc8380c9a b/toolchain/semantics/fuzzer_corpus/53ac25de61ca8f6ef9ed06f4582063bdc8380c9a
new file mode 100644
index 000000000000..ce0ba783896e
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/53ac25de61ca8f6ef9ed06f4582063bdc8380c9a
@@ -0,0 +1,16 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  // CHECK:STDERR: SYNTAX ERROR: fail_block_quotes_not_on_own_line.carbon:[[@LINE+1]]: Invalid block string: Should end with triple quotes: error: closing '''
+  var s: String = '''
+    error: closing ''' is not on its own line.
+  ''';
+
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/54bd36f9dc54f3a8ba2462aaf7203360c74c0eff b/toolchain/semantics/fuzzer_corpus/54bd36f9dc54f3a8ba2462aaf7203360c74c0eff
new file mode 100644
index 000000000000..a00c432768b8
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/54bd36f9dc54f3a8ba2462aaf7203360c74c0eff
@@ -0,0 +1,26 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 3
+
+package ExplorerTest api;
+
+interface Frob {
+  let Result:! type;
+  fn F[self: Self]() -> Result;
+}
+
+fn Use[T:! Frob where .Result = .Self](x: T) -> T {
+  var v: T = x.F();
+  return v;
+}
+
+impl i32 as Frob where .Result = i32 {
+  fn F[self: Self]() -> i32 { return self + 1; }
+}
+
+fn Main() -> i32 {
+  return Use(2);
+}
diff --git a/toolchain/semantics/fuzzer_corpus/557e6261740982882c25ec653adb828d1fd636d9 b/toolchain/semantics/fuzzer_corpus/557e6261740982882c25ec653adb828d1fd636d9
new file mode 100644
index 000000000000..67765a9097f9
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/557e6261740982882c25ec653adb828d1fd636d9
@@ -0,0 +1,28 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 5
+
+package ExplorerTest api;
+
+interface ConvertsFromInt {
+  require i32 impls ImplicitAs(Self);
+}
+
+fn ConvertIntTo(T:! ConvertsFromInt, n: i32) -> T {
+  return n;
+}
+
+class IntHolder {
+  var n: i32;
+}
+impl i32 as ImplicitAs(IntHolder) {
+  fn Convert[self: Self]() -> IntHolder { return {.n = self}; }
+}
+impl IntHolder as ConvertsFromInt {}
+
+fn Main() -> i32 {
+  return ConvertIntTo(IntHolder, 5).n;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/55b33f1ae3ad484d9adbe539da4055e6e12e8737 b/toolchain/semantics/fuzzer_corpus/55b33f1ae3ad484d9adbe539da4055e6e12e8737
new file mode 100644
index 000000000000..4a3436edd4d7
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/55b33f1ae3ad484d9adbe539da4055e6e12e8737
@@ -0,0 +1,20 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  var s: String = '''
+    A "block" ""string"" literal
+      with indent.
+    ''';
+  if (s == "A \"block\" \"\"string\"\" literal\n  with indent.\n") {
+    return 0;
+  } else {
+    return 1;
+  }
+}
diff --git a/toolchain/semantics/fuzzer_corpus/564500cfc2d733d6691063b77ec9685c1aca5326 b/toolchain/semantics/fuzzer_corpus/564500cfc2d733d6691063b77ec9685c1aca5326
new file mode 100644
index 000000000000..9cdc1992b14e
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/564500cfc2d733d6691063b77ec9685c1aca5326
@@ -0,0 +1,77 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+interface I {
+  fn F() -> i32;
+  fn M[self: Self]() -> i32;
+}
+class A {
+  var n: i32;
+  extend impl as I {
+    fn F() -> i32 { return 1; }
+    fn M[self: Self]() -> i32 { return 2; }
+  }
+  fn G[self: Self]() -> i32 { return 3; }
+}
+impl i32 as I {
+  fn F() -> i32 { return 4; }
+  fn M[self: Self]() -> i32 { return 5; }
+}
+
+alias IF = I.F;
+alias IM = I.M;
+alias AIF = A.(IF);
+alias AIM = A.(IM);
+alias AG = A.G;
+alias i32IF = i32.(IF);
+alias i32IM = i32.(IM);
+
+fn Main() -> i32 {
+  var a: A = {.n = 0};
+  if (A.(IF)() != 1) {
+    return 1;
+  }
+  if (a.(IF)() != 1) {
+    return 2;
+  }
+  if (a.(IM)() != 2) {
+    return 3;
+  }
+  if (a.(A.(IM))() != 2) {
+    return 4;
+  }
+  if (AIF() != 1) {
+    return 5;
+  }
+  if (a.(AIM)() != 2) {
+    return 6;
+  }
+  if (a.(AG)() != 3) {
+    return 7;
+  }
+  if (i32.(IF)() != 4) {
+    return 8;
+  }
+  if (0.(IF)() != 4) {
+    return 9;
+  }
+  if (0.(IM)() != 5) {
+    return 10;
+  }
+  if (0.(i32.(IM))() != 5) {
+    return 11;
+  }
+  if (i32IF() != 4) {
+    return 12;
+  }
+  if (0.(i32IM)() != 5) {
+    return 13;
+  }
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/57b625d24d4e508e02fd4d013c5b8542b01925a2 b/toolchain/semantics/fuzzer_corpus/57b625d24d4e508e02fd4d013c5b8542b01925a2
new file mode 100644
index 000000000000..2e0266db484d
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/57b625d24d4e508e02fd4d013c5b8542b01925a2
@@ -0,0 +1,14 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  {
+    // CHECK:STDERR: SYNTAX ERROR: fail_block.carbon:[[@LINE+1]]: syntax error, unexpected RETURN, expecting PERIOD or RIGHT_CURLY_BRACE
+    return 0;
+  }
+}
diff --git a/toolchain/semantics/fuzzer_corpus/585e5c74fac0d5cee731959d16d129154a776dd8 b/toolchain/semantics/fuzzer_corpus/585e5c74fac0d5cee731959d16d129154a776dd8
new file mode 100644
index 000000000000..717fd816a49f
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/585e5c74fac0d5cee731959d16d129154a776dd8
@@ -0,0 +1,22 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+class ConvertTo(T:! type) {
+  var v: T;
+  extend impl as ImplicitAs(T) {
+    fn Convert[self: Self]() -> T { return self.v; }
+  }
+}
+
+fn Main() -> i32 {
+  // CHECK:STDERR: COMPILATION ERROR: fail_intrinsic_no_convert.carbon:[[@LINE+3]]: type error in __intrinsic_assert argument 0
+  // CHECK:STDERR: expected: bool
+  // CHECK:STDERR: actual: class ConvertTo(T = bool)
+  __intrinsic_assert({.v = true} as ConvertTo(bool), {.v = "Pass"} as ConvertTo(String));
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/58f5a5b2c0b164ab3ab191696c790a041a5b14c1 b/toolchain/semantics/fuzzer_corpus/58f5a5b2c0b164ab3ab191696c790a041a5b14c1
new file mode 100644
index 000000000000..6df132e2d9ee
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/58f5a5b2c0b164ab3ab191696c790a041a5b14c1
@@ -0,0 +1,41 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: (*c).a: 1
+// CHECK:STDOUT: (*c).Foo(): 1
+// CHECK:STDOUT: (*c).Bar(): 1
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+base class C {
+  var a: i32;
+  fn Foo[self: Self]() -> i32 {
+    return 1;
+  }
+  fn Bar() -> i32 {
+    return 1;
+  }
+}
+
+class D {
+  extend base: C;
+  var b: i32;
+  fn Foo[self: Self]() -> i32 {
+    return 2;
+  }
+  fn Bar() -> i32 {
+    return 2;
+  }
+}
+
+fn Main() -> i32 {
+  var d: D = { .base = {.a = 1}, .b = 2 };
+  var c: C* = &d;
+  Print("(*c).a: {0}", (*c).a);
+  Print("(*c).Foo(): {0}", (*c).Foo());
+  Print("(*c).Bar(): {0}", (*c).Bar());
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/595a50f41bad8481dd7dc4d2dde4691c48645254 b/toolchain/semantics/fuzzer_corpus/595a50f41bad8481dd7dc4d2dde4691c48645254
new file mode 100644
index 000000000000..7d5058783889
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/595a50f41bad8481dd7dc4d2dde4691c48645254
@@ -0,0 +1,20 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+fn f(x: i32) -> i32 {
+  if (x == 0) {
+    return x;
+  } else {
+    return f(x - 1);
+  }
+}
+
+fn Main() -> i32 {
+  return f(2);
+}
diff --git a/toolchain/semantics/fuzzer_corpus/5aedd13d71226154caf5100b513031d29105850b b/toolchain/semantics/fuzzer_corpus/5aedd13d71226154caf5100b513031d29105850b
new file mode 100644
index 000000000000..21963c4d3c94
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/5aedd13d71226154caf5100b513031d29105850b
@@ -0,0 +1,18 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+fn Foo() -> () {
+  returned var x: () = ();
+  return var;
+}
+
+fn Main() -> i32 {
+  Foo();
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/5b649a15ff03bc16c5037f2e2019f5bbf953a6c9 b/toolchain/semantics/fuzzer_corpus/5b649a15ff03bc16c5037f2e2019f5bbf953a6c9
new file mode 100644
index 000000000000..a4e6df96db2e
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/5b649a15ff03bc16c5037f2e2019f5bbf953a6c9
@@ -0,0 +1,38 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: Initialize c from initializing expression (return <expr>)
+// CHECK:STDOUT: 0: Heap{}, 1: !Uninit<class C>, 2: C{}
+// CHECK:STDOUT: Object created, returning
+// CHECK:STDOUT: c destroyed
+// CHECK:STDOUT: 0: Heap{}, 1: C{}, 2: !!C{}
+// CHECK:STDOUT: c destroyed
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+class C {
+  destructor[self: Self] {
+    Print("c destroyed");
+  }
+}
+
+fn CallWithReturnExpression() -> C {
+  var c: C = {};
+  heap.PrintAllocs();
+  Print("Object created, returning");
+  return c;
+}
+
+fn FromInitializingExpression_ReturnExpr() {
+  Print("Initialize c from initializing expression (return <expr>)");
+  let c: C = CallWithReturnExpression();
+  heap.PrintAllocs();
+}
+
+fn Main() -> i32 {
+  FromInitializingExpression_ReturnExpr();
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/5c4072175e53c4fd0807395cb22c147179eed87b b/toolchain/semantics/fuzzer_corpus/5c4072175e53c4fd0807395cb22c147179eed87b
new file mode 100644
index 000000000000..bd016a6746ea
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/5c4072175e53c4fd0807395cb22c147179eed87b
@@ -0,0 +1,17 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+class A {}
+
+fn Main() -> i32 {
+  var a: A = {};
+  var b: A* = &a;
+  // CHECK:STDERR: COMPILATION ERROR: fail_invalid_ptr_conversion1.carbon:[[@LINE+1]]: type error in initializer of variable: 'class A*' is not implicitly convertible to 'i32'
+  var c: i32 = b;
+  return 1;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/5d3e40b473f22a3492d91fa5ae3cdb49ba717c24 b/toolchain/semantics/fuzzer_corpus/5d3e40b473f22a3492d91fa5ae3cdb49ba717c24
new file mode 100644
index 000000000000..72e58d0acbcc
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/5d3e40b473f22a3492d91fa5ae3cdb49ba717c24
@@ -0,0 +1,17 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+fn F() -> () {
+  // CHECK:STDERR: COMPILATION ERROR: fail_explicit_with_plain_return.carbon:[[@LINE+1]]: return; should provide a return value, to match the function's signature.
+  return;
+}
+
+fn Main() -> i32 {
+  F();
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/5dd74b1e5b931d243d08196dc0d1a4c7489d045a b/toolchain/semantics/fuzzer_corpus/5dd74b1e5b931d243d08196dc0d1a4c7489d045a
new file mode 100644
index 000000000000..e7c0682fcade
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/5dd74b1e5b931d243d08196dc0d1a4c7489d045a
@@ -0,0 +1,39 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+interface Vector {
+  fn Add[self: Self](b: Self) -> Self;
+  fn Scale[self: Self](v: i32) -> Self;
+}
+
+class Point {
+  var x: i32;
+  var y: i32;
+  extend impl as Vector {
+    fn Add[self: Point](b: Point) -> Point {
+      return {.x = self.x + b.x, .y = self.y + b.y};
+    }
+    fn Scale[self: Point](v: i32) -> Point {
+      return {.x = self.x * v, .y = self.y * v};
+    }
+  }
+}
+
+fn AddAndScaleGeneric[T:! Vector](t: (T, T), s: i32) -> T {
+  var m: auto = t[0].Add;
+  var n: auto = m(t[1]).Scale;
+  return n(s);
+}
+
+fn Main() -> i32 {
+  var a: Point = {.x = 1, .y = 1};
+  var b: Point = {.x = 2, .y = 3};
+  var p: Point = AddAndScaleGeneric((a, b), 5);
+  return p.x - 15;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/6271c667c707f9f332f8d672db458d12c99a85e6 b/toolchain/semantics/fuzzer_corpus/6271c667c707f9f332f8d672db458d12c99a85e6
new file mode 100644
index 000000000000..4ad8f7d5a9f7
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/6271c667c707f9f332f8d672db458d12c99a85e6
@@ -0,0 +1,21 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+namespace A;
+namespace A.B;
+namespace A.B.C;
+fn A.B.C.
+  // CHECK:STDERR: COMPILATION ERROR: fail_missing_nested.carbon:[[@LINE+1]]: name 'D' has not been declared in namespace A.B.C
+  D
+  // Don't combine with the previous line. This test is verifying that the
+  // diagnostic points at the right token.
+  .E.F() {}
+
+fn Main() -> i32 {
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/62843918195183e17a993c061b9c88d636ca28f0 b/toolchain/semantics/fuzzer_corpus/62843918195183e17a993c061b9c88d636ca28f0
new file mode 100644
index 000000000000..f221d1e3adea
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/62843918195183e17a993c061b9c88d636ca28f0
@@ -0,0 +1,143 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// This doesn't test trace ouptut because it's too slow.
+// AUTOUPDATE
+// CHECK:STDOUT: String list length is: 7
+// CHECK:STDOUT: This is a String Entry 4
+// CHECK:STDOUT: Value 1337
+// CHECK:STDOUT: result: 0
+package ExplorerTest api;
+
+class Node(T:! type) {
+  fn Create(value: T)-> Node(T) {
+    return {
+      .value = Optional(T).Create(value),
+      .next = Optional(Node(T)*).CreateEmpty(),
+      .prev = Optional(Node(T)*).CreateEmpty()
+    };
+  }
+  fn set_next[addr self: Self*](n: Optional(Node(T)*)) {
+    (*self).next = n;
+  }
+  fn set_prev[addr self: Self*](n: Optional(Node(T)*)) {
+    (*self).prev = n;
+  }
+  var value: Optional(T);
+  var next: Optional(Node(T)*);
+  var prev: Optional(Node(T)*);
+}
+
+class LinkedList(T:! type) {
+  fn Create() -> LinkedList(T) {
+    return {
+      .head = Optional(Node(T)*).CreateEmpty(),
+      .tail = Optional(Node(T)*).CreateEmpty(),
+      .len = 0
+    };
+  }
+  fn PushBack[addr self: Self*](value:T) {
+    (*self).len = (*self).len + 1;
+    if(not (*self).head.HasValue()) {
+      (*self).head = Optional(Node(T)*).Create(heap.New(Node(T).Create(value)));
+      (*self).tail = (*self).head;
+      return;
+    }
+    var last: Optional(Node(T)*) = (*self).tail;
+    var last_value:Node(T)* = last.Get();
+    var v_wrapped:Optional(Node(T)*) = Optional(Node(T)*).Create(heap.New(Node(T).Create(value)));
+    (*last_value).set_next(v_wrapped);
+    (*v_wrapped.Get()).set_prev(last);
+    (*self).tail = v_wrapped;
+  }
+  fn PushFront[addr self: Self*](value:T) {
+    (*self).len = (*self).len + 1;
+    if(not (*self).head.HasValue()) {
+      (*self).head = Optional(Node(T)*).Create(heap.New(Node(T).Create(value)));
+      (*self).tail = (*self).head;
+      return;
+    }
+    var v_wrapped:Optional(Node(T)*) = Optional(Node(T)*).Create(heap.New(Node(T).Create(value)));
+    var current_head: Optional(Node(T)*) = (*self).head;
+    var current_head_value: Node(T)* = current_head.Get();
+    (*v_wrapped.Get()).set_next(current_head);
+    (*current_head_value).set_prev(v_wrapped);
+    (*self).head = v_wrapped;
+  }
+  fn Clear[addr self: Self*]() {
+    if((*self).len == 0) {
+      return;
+    }
+    var iter: auto = (*self).head;
+    while(iter.HasValue()) {
+      var current: auto = iter;
+      iter = (*iter.Get()).next;
+      heap.Delete(current.Get());
+    }
+    (*self).head = Optional(Node(T)*).CreateEmpty();
+    (*self).tail = Optional(Node(T)*).CreateEmpty();
+    (*self).len = 0;
+  }
+  fn Length[self: Self]() -> i32 {
+    return self.len;
+  }
+  var head: Optional(Node(T)*);
+  var tail: Optional(Node(T)*);
+  var len: i32;
+}
+
+// This function exists as a helper the context of this test case specifically and does not represent
+// the common case for index based lookups in list like structures.
+fn GetListEntryByIndex[T:! type](list: LinkedList(T)*, target_index: i32) -> Optional(T) {
+  let list_length: i32 = (*list).Length();
+  if(target_index > list_length - 1 or target_index < 0) {
+    // Not in possible range
+    return Optional(T).CreateEmpty();
+  }
+  var search_backwards:bool = target_index > list_length / 2;
+  var iter:Optional(Node(T)*) = if search_backwards then (*list).tail else (*list).head;
+  var c:i32 = if search_backwards then list_length -1 else 0;
+  while(c != target_index) {
+    var node: Node(T) = *(iter.Get());
+    if(search_backwards) {
+      c = c - 1;
+      iter = node.prev;
+    } else {
+      iter = node.next;
+      c = c + 1;
+    }
+  }
+
+  return (*(iter.Get())).value;
+}
+
+fn Main() -> i32 {
+  var test_list:auto = LinkedList(String).Create();
+  test_list.PushBack("This is a String Entry 0");
+  test_list.PushBack("This is a String Entry 1");
+  test_list.PushBack("This is a String Entry 2");
+  test_list.PushBack("This is a String Entry 3");
+  test_list.PushBack("This is a String Entry 4");
+  test_list.PushBack("This is a String Entry 5");
+  test_list.PushFront("This is a prepended String -1");
+  Print("String list length is: {0}", test_list.Length());
+  var search_index:i32 = 5;
+  var retrieved_entry: auto = GetListEntryByIndex(&test_list,search_index);
+  if(retrieved_entry.HasValue()) {
+    var retrieved_value:String = retrieved_entry.Get();
+    Print(retrieved_value);
+  } else {
+    Print("No entry found in String list for index {0}!", search_index);
+  }
+  test_list.Clear();
+
+  var second_list: auto = LinkedList(i32*).Create();
+  var number: i32 = 1337;
+  var number_ptr: i32* = &number;
+  second_list.PushBack(number_ptr);
+  var retrieved_ptr:i32* = GetListEntryByIndex(&second_list, 0).Get();
+  var value: i32 = *retrieved_ptr;
+  Print("Value {0}", value);
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/62dfbc885389ef6d5d68bf236c814ab1b50a830f b/toolchain/semantics/fuzzer_corpus/62dfbc885389ef6d5d68bf236c814ab1b50a830f
new file mode 100644
index 000000000000..6f9f6d3894d5
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/62dfbc885389ef6d5d68bf236c814ab1b50a830f
@@ -0,0 +1,17 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+interface IFace {}
+
+impl {.IFace : (type where type == i32 and type == i32 and type == i32, )} as IFace {
+}
+
+fn Main() -> i32 {
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/6587b22ba1c43ce2feb22483a911799a4d0b4864 b/toolchain/semantics/fuzzer_corpus/6587b22ba1c43ce2feb22483a911799a4d0b4864
new file mode 100644
index 000000000000..93d0662f6bbb
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/6587b22ba1c43ce2feb22483a911799a4d0b4864
@@ -0,0 +1,20 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+// Test that assignment performs a copy and does not create an alias.
+
+fn Main() -> i32 {
+  var x: i32 = -1;
+  if (true) {
+    var y: i32 = 0;
+    x = y;
+    // y dies here
+  }
+  return x;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/66246b4676440f9d7e081eeba1db52967485be20 b/toolchain/semantics/fuzzer_corpus/66246b4676440f9d7e081eeba1db52967485be20
new file mode 100644
index 000000000000..95fe1a28a198
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/66246b4676440f9d7e081eeba1db52967485be20
@@ -0,0 +1,14 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 3
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  var t: auto = (1, 2);
+  var a: [i32; 2] = t;
+  return a[0] + a[1];
+}
diff --git a/toolchain/semantics/fuzzer_corpus/668a14b9e1911baad9eb3b1029bce4fa4cb22c50 b/toolchain/semantics/fuzzer_corpus/668a14b9e1911baad9eb3b1029bce4fa4cb22c50
new file mode 100644
index 000000000000..1db423532beb
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/668a14b9e1911baad9eb3b1029bce4fa4cb22c50
@@ -0,0 +1,13 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  var x: [i32; 2] = (0, 1);
+  // CHECK:STDERR: RUNTIME ERROR: fail_index.carbon:[[@LINE+1]]: index 2 out of range in (0, 1)
+  return x[2];
+}
diff --git a/toolchain/semantics/fuzzer_corpus/674b0a11f56cfc231154426154f979971f269f04 b/toolchain/semantics/fuzzer_corpus/674b0a11f56cfc231154426154f979971f269f04
new file mode 100644
index 000000000000..599ee7820979
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/674b0a11f56cfc231154426154f979971f269f04
@@ -0,0 +1,23 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 3
+
+package ExplorerTest api;
+
+// The bodies of member functions are processed after all immediately enclosing
+// classes, impl declarations, and interfaces.
+class A {
+  fn F[self: Self]() -> i32 {
+    return G() + self.H();
+  }
+  fn G() -> i32 { return 1; }
+  fn H[self: Self]() -> i32 { return 2; }
+}
+
+fn Main() -> i32 {
+  var a: A = {};
+  return a.F();
+}
diff --git a/toolchain/semantics/fuzzer_corpus/676a9a2e7d85dd808d2d0ba40a0f73713ffb6836 b/toolchain/semantics/fuzzer_corpus/676a9a2e7d85dd808d2d0ba40a0f73713ffb6836
new file mode 100644
index 000000000000..286f573d5c66
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/676a9a2e7d85dd808d2d0ba40a0f73713ffb6836
@@ -0,0 +1,17 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 3
+
+package ExplorerTest api;
+
+fn AddInt(a: i32, b: i32) -> i32 {
+  returned var ret: i32 = a + b;
+  return var;
+}
+
+fn Main() -> i32 {
+  return AddInt(1, 2);
+}
diff --git a/toolchain/semantics/fuzzer_corpus/6967d4554a79d967765e2f4f4f4d9f660388ae35 b/toolchain/semantics/fuzzer_corpus/6967d4554a79d967765e2f4f4f4d9f660388ae35
new file mode 100644
index 000000000000..a5c9fcdb3108
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/6967d4554a79d967765e2f4f4f4d9f660388ae35
@@ -0,0 +1,13 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  // CHECK:STDERR: RUNTIME ERROR: fail_overflow_div.carbon:[[@LINE+1]]: integer overflow
+  var a: auto = (-2147483647 -1) /-1;
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/69c04a4e172b38ee2bd233cf2e16bc54e64f86c8 b/toolchain/semantics/fuzzer_corpus/69c04a4e172b38ee2bd233cf2e16bc54e64f86c8
new file mode 100644
index 000000000000..3efac610b817
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/69c04a4e172b38ee2bd233cf2e16bc54e64f86c8
@@ -0,0 +1,14 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 1
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  var (x: i32, y: i32);
+  x = 1;
+  return x;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/6bacf9e89d7d4ecc9d6fd27310cccdd491d03040 b/toolchain/semantics/fuzzer_corpus/6bacf9e89d7d4ecc9d6fd27310cccdd491d03040
new file mode 100644
index 000000000000..a9d7c40c116b
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/6bacf9e89d7d4ecc9d6fd27310cccdd491d03040
@@ -0,0 +1,17 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+fn Id(t: type) -> auto { return t; }
+
+// Test non-trivial type expression in variable declaration statement.
+
+fn Main() -> i32 {
+  var x: Id(i32) = 0;
+  return x;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/6bee596e11d3b23cb1b5a66320949a056ed670a7 b/toolchain/semantics/fuzzer_corpus/6bee596e11d3b23cb1b5a66320949a056ed670a7
new file mode 100644
index 000000000000..f6562f988e01
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/6bee596e11d3b23cb1b5a66320949a056ed670a7
@@ -0,0 +1,37 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+interface Number {
+  fn Zero() -> Self;
+  fn Add[self: Self](other: Self) -> Self;
+}
+
+class Point(T:! Number) {
+  fn Origin() -> Point(T) {
+    return {.x = T.Zero(), .y = T.Zero()};
+  }
+  fn Clone[self: Point(T)]() -> Point(T) {
+    return {.x = self.x, .y = self.y};
+  }
+  fn SumXY[self: Point(T)]() -> T {
+    return self.x.Add(self.y);
+  }
+  var x: T;
+  var y: T;
+}
+
+impl i32 as Number {
+  fn Zero() -> i32 { return 0; }
+  fn Add[self: i32](other: i32) -> i32 { return self + other; }
+}
+
+fn Main() -> i32 {
+  var p: Point(i32) = Point(i32).Origin();
+  return p.Clone().SumXY();
+}
diff --git a/toolchain/semantics/fuzzer_corpus/6ca9f18aa125c49880d2596552e3faa81c63efb3 b/toolchain/semantics/fuzzer_corpus/6ca9f18aa125c49880d2596552e3faa81c63efb3
new file mode 100644
index 000000000000..13c4f8b56ad1
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/6ca9f18aa125c49880d2596552e3faa81c63efb3
@@ -0,0 +1,16 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+fn BadSimpleMemberAccess[T:! type](a: T) -> T {
+  // CHECK:STDERR: COMPILATION ERROR: fail_field_access_on_generic.carbon:[[@LINE+1]]: member access in unconstrained type
+  return a.x;
+}
+
+fn Main() -> i32 {
+  return BadSimpleMemberAccess(0);
+}
diff --git a/toolchain/semantics/fuzzer_corpus/6d1d2d78afae37c48771a7d9e1ebb943b4043d6e b/toolchain/semantics/fuzzer_corpus/6d1d2d78afae37c48771a7d9e1ebb943b4043d6e
new file mode 100644
index 000000000000..700cb6a070ab
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/6d1d2d78afae37c48771a7d9e1ebb943b4043d6e
@@ -0,0 +1,15 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+var x: i32 = 0;
+
+fn Main() -> i32 {
+  var x: i32 = 0;
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/6e17f17d5bfc65e44683079702a3ff6fb2eb5599 b/toolchain/semantics/fuzzer_corpus/6e17f17d5bfc65e44683079702a3ff6fb2eb5599
new file mode 100644
index 000000000000..a633e90577ac
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/6e17f17d5bfc65e44683079702a3ff6fb2eb5599
@@ -0,0 +1,13 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDERR: RUNTIME ERROR: {{.*}}/explorer/data/prelude.carbon:{{.*}}: Integer overflow
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  var a: auto = 5 << -1;
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/6ec937ca4086b447092cfc13d8d2e77c9536cf24 b/toolchain/semantics/fuzzer_corpus/6ec937ca4086b447092cfc13d8d2e77c9536cf24
new file mode 100644
index 000000000000..f4f4cf654b19
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/6ec937ca4086b447092cfc13d8d2e77c9536cf24
@@ -0,0 +1,20 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  var s: String = #'''
+    A block string literal
+    \#'''#
+    '''#;
+  if (s == "A block string literal\n'''#\n") {
+    return 0;
+  } else {
+    return 1;
+  }
+}
diff --git a/toolchain/semantics/fuzzer_corpus/7210b63a30c6f2ca76270eeca909274971db9b36 b/toolchain/semantics/fuzzer_corpus/7210b63a30c6f2ca76270eeca909274971db9b36
new file mode 100644
index 000000000000..dacedd79e935
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/7210b63a30c6f2ca76270eeca909274971db9b36
@@ -0,0 +1,13 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  var a: [i32;] = ();
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/723771f1826c803bbd50afe6e703268a89d6edab b/toolchain/semantics/fuzzer_corpus/723771f1826c803bbd50afe6e703268a89d6edab
new file mode 100644
index 000000000000..c83b78705689
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/723771f1826c803bbd50afe6e703268a89d6edab
@@ -0,0 +1,8 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+// CHECK:STDERR: SYNTAX ERROR: fail_invalid_char.carbon:[[@LINE+1]]: invalid character '\xEF' in source file.
+�
diff --git a/toolchain/semantics/fuzzer_corpus/7317dc5445182496edbdede5df5cc895f598dd2f b/toolchain/semantics/fuzzer_corpus/7317dc5445182496edbdede5df5cc895f598dd2f
new file mode 100644
index 000000000000..e3ad9a23a777
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/7317dc5445182496edbdede5df5cc895f598dd2f
@@ -0,0 +1,40 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+__mixin Operations {
+  fn Square[self: Self](x:i32) -> i32{
+    return x * x;
+  }
+}
+
+class Point {
+  var x: i32;
+  var y: i32;
+  fn DistanceSquare[self: Self](other:Self) -> i32 {
+    return self.Square(self.x - other.x) + self.Square(self.y - other.y);
+  }
+  __mix Operations;
+}
+
+class Complex {
+  var r: i32;
+  var i: i32;
+  __mix Operations;
+  fn AbsSquare[self: Self]() -> i32 {
+    return self.Square(self.r) + self.Square(self.i);
+  }
+}
+
+
+fn Main() -> i32 {
+  var p1: Point = {.x = 1, .y = 2 };
+  var p2: Point = {.x = 4, .y = 3 };
+  var c: Complex = {.r = 5, .i = 6 };
+  return c.AbsSquare() - p1.DistanceSquare(p2) - 51;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/738455622faabb9ac57e4742ab9774f277769d1d b/toolchain/semantics/fuzzer_corpus/738455622faabb9ac57e4742ab9774f277769d1d
new file mode 100644
index 000000000000..c28e620b92a0
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/738455622faabb9ac57e4742ab9774f277769d1d
@@ -0,0 +1,18 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+interface HasThreeTypes {
+  let A:! type;
+  let B:! type;
+  let C:! type;
+}
+
+// CHECK:STDERR: COMPILATION ERROR: fail_incomplete_impl_2.carbon:[[@LINE+1]]: implementation doesn't provide a concrete value for interface HasThreeTypes.C
+impl i32 as HasThreeTypes where .A = i32 and .B = .C {}
+
+fn Main() -> i32 { return 0; }
diff --git a/toolchain/semantics/fuzzer_corpus/738e3314d89604cb56233d3d1d985b895264250f b/toolchain/semantics/fuzzer_corpus/738e3314d89604cb56233d3d1d985b895264250f
new file mode 100644
index 000000000000..68076512a659
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/738e3314d89604cb56233d3d1d985b895264250f
@@ -0,0 +1,33 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 3
+
+package ExplorerTest api;
+
+choice Opt {
+  None(),
+  Some(i32)
+}
+
+fn A(a: Opt, b: Opt) -> i32 {
+  match ((a, b)) {
+    case (Opt.Some(n: i32), _: auto) => { return n; }
+    case (_: auto, Opt.Some(n: i32)) => { return n; }
+    case (Opt.None(), Opt.None()) => { return 0; }
+  }
+}
+
+fn B(a: Opt, b: Opt) -> i32 {
+  match ((a, b)) {
+    case (Opt.None(), _: auto) => { return 0; }
+    case (Opt.Some(n: i32), Opt.None()) => { return n; }
+    case (Opt.Some(n: i32), Opt.Some(m: i32)) => { return n + m; }
+  }
+}
+
+fn Main() -> i32 {
+  return A(Opt.None(), Opt.Some(1)) + B(Opt.Some(2), Opt.None());
+}
diff --git a/toolchain/semantics/fuzzer_corpus/73b4d1aee1031af813cfe9efbf1427f3b2d10f6b b/toolchain/semantics/fuzzer_corpus/73b4d1aee1031af813cfe9efbf1427f3b2d10f6b
new file mode 100644
index 000000000000..d95c1ecc7337
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/73b4d1aee1031af813cfe9efbf1427f3b2d10f6b
@@ -0,0 +1,21 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 3
+
+package ExplorerTest api;
+
+fn AddInt(a: i32, b: i32) -> i32 {
+  if (a == b) {
+    returned var ret: i32 = a + b;
+    return var;
+  } else {
+    return a + b;
+  }
+}
+
+fn Main() -> i32 {
+  return AddInt(1, 2);
+}
diff --git a/toolchain/semantics/fuzzer_corpus/73da4596259bfcfb0dc1a29e39f7c3b0944b1e32 b/toolchain/semantics/fuzzer_corpus/73da4596259bfcfb0dc1a29e39f7c3b0944b1e32
new file mode 100644
index 000000000000..78a52935a83d
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/73da4596259bfcfb0dc1a29e39f7c3b0944b1e32
@@ -0,0 +1,18 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+fn DoNothing() {
+  // Empty block
+}
+
+fn Main() -> i32 {
+  var x: i32 = 0;
+  DoNothing();
+  return x;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/741d81851f3d0d1ad8e1a1b2584d04390c1de134 b/toolchain/semantics/fuzzer_corpus/741d81851f3d0d1ad8e1a1b2584d04390c1de134
new file mode 100644
index 000000000000..e6b07fcdb4d4
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/741d81851f3d0d1ad8e1a1b2584d04390c1de134
@@ -0,0 +1,25 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: ab.a: 2
+// CHECK:STDOUT: ab.b: 1
+// CHECK:STDOUT: ba.a: 2
+// CHECK:STDOUT: ba.b: 1
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+alias AB = {.a: i32, .b: i32};
+alias BA = {.b: i32, .a: i32};
+
+fn Main() -> i32 {
+  var ab: AB = {.b = 1, .a = 2};
+  var ba: BA = ab;
+  Print("ab.a: {0}", ab.a);
+  Print("ab.b: {0}", ab.b);
+  Print("ba.a: {0}", ba.a);
+  Print("ba.b: {0}", ba.b);
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/7439f0e12680c8328592155e4b3b38db983860ad b/toolchain/semantics/fuzzer_corpus/7439f0e12680c8328592155e4b3b38db983860ad
new file mode 100644
index 000000000000..f0efb8b74d9d
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/7439f0e12680c8328592155e4b3b38db983860ad
@@ -0,0 +1,13 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  var v: [i32; 2];
+  // CHECK:STDERR: COMPILATION ERROR: fail_array.carbon:[[@LINE+1]]: use of uninitialized variable v
+  return v[0];
+}
diff --git a/toolchain/semantics/fuzzer_corpus/743bcc2582c9d359eb545c9c2234b31d20686ab1 b/toolchain/semantics/fuzzer_corpus/743bcc2582c9d359eb545c9c2234b31d20686ab1
new file mode 100644
index 000000000000..d25ef02db91a
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/743bcc2582c9d359eb545c9c2234b31d20686ab1
@@ -0,0 +1,18 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 1
+
+package ExplorerTest api;
+
+fn map[T:! type](f: __Fn (T) -> T, tuple: (T, T)) -> (T, T) {
+  return (f(tuple[0]), f(tuple[1]));
+}
+
+fn inc(x: i32) -> i32 { return x + 1; }
+
+fn Main() -> i32 {
+  return map(inc, (0, 2))[0];
+}
diff --git a/toolchain/semantics/fuzzer_corpus/74668979673c76a468906cbf4fb6c6807deb1ce7 b/toolchain/semantics/fuzzer_corpus/74668979673c76a468906cbf4fb6c6807deb1ce7
new file mode 100644
index 000000000000..12f90d6a4d92
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/74668979673c76a468906cbf4fb6c6807deb1ce7
@@ -0,0 +1,13 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  // CHECK:STDERR: COMPILATION ERROR: fail_size_mismatch.carbon:[[@LINE+1]]: type error in initializer of variable: '(i32, i32, i32)' is not implicitly convertible to '[i32; 2]'
+  var x: [i32; 2] = (0, 1, 2);
+  return x[0];
+}
diff --git a/toolchain/semantics/fuzzer_corpus/766f0c11773ae0fa80bdb4e441c61024fe08dbfa b/toolchain/semantics/fuzzer_corpus/766f0c11773ae0fa80bdb4e441c61024fe08dbfa
new file mode 100644
index 000000000000..8441a4200d53
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/766f0c11773ae0fa80bdb4e441c61024fe08dbfa
@@ -0,0 +1,20 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+class C(T:! type) {}
+
+fn F(T:! type) -> type {
+  return C(T);
+}
+
+fn Main() -> i32 {
+  var v: F(i32) = {};
+  var w: C(i32) = v;
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/76aa1704b7412be324a2fc194e4aaf03c0aae190 b/toolchain/semantics/fuzzer_corpus/76aa1704b7412be324a2fc194e4aaf03c0aae190
new file mode 100644
index 000000000000..17590b9c9364
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/76aa1704b7412be324a2fc194e4aaf03c0aae190
@@ -0,0 +1,13 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  // CHECK:STDERR: RUNTIME ERROR: fail_mod_by_zero.carbon:[[@LINE+1]]: division by zero
+  var a: auto = 5 % 0;
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/789722555be3fb72c649473531436974c36c0b99 b/toolchain/semantics/fuzzer_corpus/789722555be3fb72c649473531436974c36c0b99
new file mode 100644
index 000000000000..b9d27ad8d582
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/789722555be3fb72c649473531436974c36c0b99
@@ -0,0 +1,51 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: c.Foo(): 1
+// CHECK:STDOUT: d.Foo(): 2
+// CHECK:STDOUT: e.Foo(): 3
+// CHECK:STDOUT: (*dp).Foo(): 3
+// CHECK:STDOUT: (*dc).Foo(): 3
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+base class C {
+  var value_c: i32;
+  virtual fn Foo[self: Self]() -> i32 {
+    return self.value_c;
+  }
+}
+
+base class D {
+  extend base: C;
+  var value_d: i32;
+  impl fn Foo[self: Self]() -> i32 {
+    return self.value_d;
+  }
+}
+
+class E {
+  extend base: D;
+  var value_e: i32;
+  impl fn Foo[self: Self]() -> i32 {
+    return self.value_e;
+  }
+}
+
+fn Main() -> i32 {
+  var c: C = {.value_c = 1};
+  Print("c.Foo(): {0}", c.Foo());
+  var d: D = {.value_d = 2, .base = {.value_c = 1}};
+  Print("d.Foo(): {0}", d.Foo());
+  var e: E = {.value_e = 3, .base={.value_d = 2, .base = {.value_c = 1}}};
+  Print("e.Foo(): {0}", e.Foo());
+  var dp: D* = &e;
+  Print("(*dp).Foo(): {0}", (*dp).Foo());
+  var dc: C* = &e;
+  Print("(*dc).Foo(): {0}", (*dc).Foo());
+
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/78b31fa3b989055733f498c49e86a6211e1316bc b/toolchain/semantics/fuzzer_corpus/78b31fa3b989055733f498c49e86a6211e1316bc
new file mode 100644
index 000000000000..23dbe9af936a
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/78b31fa3b989055733f498c49e86a6211e1316bc
@@ -0,0 +1,16 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  // CHECK:STDERR: SYNTAX ERROR: fail_raw_block_quotes_not_on_own_line.carbon:[[@LINE+1]]: Invalid block string: Should end with triple quotes: error: closing '''
+  var s: String = #'''
+    error: closing '''# is not on its own line.
+  '''#;
+
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/795411f0b98335ca22f12b48b685bde1fc75bb61 b/toolchain/semantics/fuzzer_corpus/795411f0b98335ca22f12b48b685bde1fc75bb61
new file mode 100644
index 000000000000..5cffe47f0b68
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/795411f0b98335ca22f12b48b685bde1fc75bb61
@@ -0,0 +1,40 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+choice AB {
+  A(),
+  B()
+}
+
+fn F() -> AB { return AB.A(); }
+
+fn Main() -> i32 {
+  // This is T9 from http://moscova.inria.fr/~maranget/papers/warn/warn014.html
+  // Note, this match is exhaustive, but it exceeds our depth limit.
+  match ((F(), F(), F(), F(), F(), F(), F(), F(), F())) {
+    case (AB.A(), AB.A(), AB.A(), AB.A(), AB.A(), AB.A(), AB.A(), AB.A(), AB.A()) => { return 0; }
+    case (AB.B(), AB.B(), AB.B(), AB.B(), AB.B(), AB.B(), AB.B(), AB.B(), AB.B()) => { return 1; }
+    case (_: AB,  AB.A(), AB.A(), AB.A(), AB.A(), AB.A(), AB.A(), AB.A(), AB.A()) => { return 2; }
+    case (_: AB,  AB.B(), AB.B(), AB.B(), AB.B(), AB.B(), AB.B(), AB.B(), AB.B()) => { return 3; }
+    case (_: AB,  _: AB,  AB.A(), AB.A(), AB.A(), AB.A(), AB.A(), AB.A(), AB.A()) => { return 4; }
+    case (_: AB,  _: AB,  AB.B(), AB.B(), AB.B(), AB.B(), AB.B(), AB.B(), AB.B()) => { return 5; }
+    case (_: AB,  _: AB,  _: AB,  AB.A(), AB.A(), AB.A(), AB.A(), AB.A(), AB.A()) => { return 6; }
+    case (_: AB,  _: AB,  _: AB,  AB.B(), AB.B(), AB.B(), AB.B(), AB.B(), AB.B()) => { return 7; }
+    case (_: AB,  _: AB,  _: AB,  _: AB,  AB.A(), AB.A(), AB.A(), AB.A(), AB.A()) => { return 8; }
+    case (_: AB,  _: AB,  _: AB,  _: AB,  AB.B(), AB.B(), AB.B(), AB.B(), AB.B()) => { return 9; }
+    case (_: AB,  _: AB,  _: AB,  _: AB,  _: AB,  AB.A(), AB.A(), AB.A(), AB.A()) => { return 10; }
+    case (_: AB,  _: AB,  _: AB,  _: AB,  _: AB,  AB.B(), AB.B(), AB.B(), AB.B()) => { return 11; }
+    case (_: AB,  _: AB,  _: AB,  _: AB,  _: AB,  _: AB,  AB.A(), AB.A(), AB.A()) => { return 12; }
+    case (_: AB,  _: AB,  _: AB,  _: AB,  _: AB,  _: AB,  AB.B(), AB.B(), AB.B()) => { return 13; }
+    case (_: AB,  _: AB,  _: AB,  _: AB,  _: AB,  _: AB,  _: AB,  AB.A(), AB.A()) => { return 14; }
+    case (_: AB,  _: AB,  _: AB,  _: AB,  _: AB,  _: AB,  _: AB,  AB.B(), AB.B()) => { return 15; }
+    case (_: AB,  _: AB,  _: AB,  _: AB,  _: AB,  _: AB,  _: AB,  _: AB,  AB.A()) => { return 16; }
+    case (_: AB,  _: AB,  _: AB,  _: AB,  _: AB,  _: AB,  _: AB,  _: AB,  AB.B()) => { return 17; }
+  }
+// CHECK:STDERR: COMPILATION ERROR: fail_exhaustive_exponential_series_t.carbon:[[@LINE+1]]: non-exhaustive match may allow control-flow to reach the end of a function that provides a `->` return type
+}
diff --git a/toolchain/semantics/fuzzer_corpus/7a20636f05cc0619b0d09767f2f804541e9b1db7 b/toolchain/semantics/fuzzer_corpus/7a20636f05cc0619b0d09767f2f804541e9b1db7
new file mode 100644
index 000000000000..d99c8f53d2b0
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/7a20636f05cc0619b0d09767f2f804541e9b1db7
@@ -0,0 +1,15 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  var (x: auto, y: [i32;]) = (42, (0, 1));
+  var index: i32 = 1;
+  y[index] = 0;
+  return y[0] + y[1];
+}
diff --git a/toolchain/semantics/fuzzer_corpus/7b5a8347300b3181cd2cf471a26b4d1849cd736d b/toolchain/semantics/fuzzer_corpus/7b5a8347300b3181cd2cf471a26b4d1849cd736d
new file mode 100644
index 000000000000..283c002f6392
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/7b5a8347300b3181cd2cf471a26b4d1849cd736d
@@ -0,0 +1,24 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+// This tests the call-by-value aspect of parameter passing.
+// This makes sure that when the value in `x` dies,
+// it does not cause the value in `a` to also die.
+
+fn f(x: i32) -> i32 {
+  return 0;
+}
+
+fn Main() -> i32 {
+  var a: i32 = 0;
+  var b: i32 = 1;
+  f(a);
+  b = a;
+  return b;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/7bb08a33952aae009b591d3cf1f9bb883fb0d552 b/toolchain/semantics/fuzzer_corpus/7bb08a33952aae009b591d3cf1f9bb883fb0d552
new file mode 100644
index 000000000000..dadcc9096844
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/7bb08a33952aae009b591d3cf1f9bb883fb0d552
@@ -0,0 +1,29 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 12
+
+package Foo api;
+interface A {
+  fn F[self: Self]() -> i32;
+}
+interface B {
+  fn G(o: Self) -> i32;
+}
+alias C = A & B;
+class X {
+  extend impl as A {
+    fn F[self: Self]() -> i32 { return 10 * self.n; }
+  }
+  extend impl as B {
+    fn G(o: Self) -> i32 { return o.n; }
+  }
+  var n: i32;
+}
+fn Main() -> i32 {
+  var v: X = {.n = 1};
+  var w: X = {.n = 2};
+  return v.(C.F)() + X.(C.G)(w);
+}
diff --git a/toolchain/semantics/fuzzer_corpus/7c43b3e05d4290ec1321e4780fefb13ab78971df b/toolchain/semantics/fuzzer_corpus/7c43b3e05d4290ec1321e4780fefb13ab78971df
new file mode 100644
index 000000000000..b2999c35ff81
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/7c43b3e05d4290ec1321e4780fefb13ab78971df
@@ -0,0 +1,13 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  // CHECK:STDERR: SYNTAX ERROR: fail_hex_lower.carbon:[[@LINE+1]]: Invalid escaping in string: "str\xaa"
+  Print("str\xaa");
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/7cf48bc097227836f096053ec92498c72e03f61c b/toolchain/semantics/fuzzer_corpus/7cf48bc097227836f096053ec92498c72e03f61c
new file mode 100644
index 000000000000..6e35b6d2efbf
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/7cf48bc097227836f096053ec92498c72e03f61c
@@ -0,0 +1,18 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  var x: i32 = 0;
+  match (x) {
+    case 1 => {
+      return 1;
+    }
+  }
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/7d517287eeb3fe4793d29afa7dbaea8ad67ac795 b/toolchain/semantics/fuzzer_corpus/7d517287eeb3fe4793d29afa7dbaea8ad67ac795
new file mode 100644
index 000000000000..225922c4dfa0
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/7d517287eeb3fe4793d29afa7dbaea8ad67ac795
@@ -0,0 +1,36 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: DESTRUCTOR A 1
+// CHECK:STDOUT: DESTRUCTOR B 2
+// CHECK:STDOUT: result: 1
+
+package ExplorerTest api;
+
+class A{
+    class B{
+        destructor[self: Self]{
+            Print("DESTRUCTOR B {0}",self.n);
+        }
+        fn Create(x: i32) -> B{
+           return {.n = x };
+        }
+        var n: i32;
+    }
+
+    destructor[self: Self]{
+        Print("DESTRUCTOR A {0}",self.n);
+    }
+    fn Create(x: i32) -> A{
+        return {.n = x, .b = B.Create(2)};
+    }
+    var n: i32;
+    var b : B;
+}
+
+fn Main() -> i32 {
+  var a: A = A.Create(1);
+  return 1;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/7d621f229fa589942992db52f964d08c90debaf8 b/toolchain/semantics/fuzzer_corpus/7d621f229fa589942992db52f964d08c90debaf8
new file mode 100644
index 000000000000..1321501ab9c2
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/7d621f229fa589942992db52f964d08c90debaf8
@@ -0,0 +1,12 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+namespace N;
+
+fn Main() -> i32 { return 0; }
diff --git a/toolchain/semantics/fuzzer_corpus/7e458fdfd466476c1bbe4095f5d224a6ea4867d6 b/toolchain/semantics/fuzzer_corpus/7e458fdfd466476c1bbe4095f5d224a6ea4867d6
new file mode 100644
index 000000000000..e21c2e0619cb
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/7e458fdfd466476c1bbe4095f5d224a6ea4867d6
@@ -0,0 +1,62 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+interface AddMul {
+  fn Add[self: Self](o: Self) -> Self;
+  fn Mul[self: Self](o: Self) -> Self;
+}
+
+impl i32 as AddMul {
+  fn Add[self: i32](o: i32) -> i32 {
+    return self + o;
+  }
+  fn Mul[self: i32](o: i32) -> i32 {
+    return self * o;
+  }
+}
+
+class Holder(T:! AddMul) {
+  var v: T;
+}
+
+interface Vector(Scalar:! AddMul) {
+  fn Zero() -> Self;
+  fn Add[self: Self](b: Self) -> Self;
+  fn Scale[self: Self](v: Scalar) -> Self;
+  fn Hold[self: Self](v: Scalar) -> Holder(Scalar);
+}
+
+class Point {
+  var x: i32;
+  var y: i32;
+  extend impl as Vector(i32) {
+    fn Zero() -> Point {
+      return {.x = 0, .y = 0};
+    }
+    fn Add[self: Point](b: Point) -> Point {
+      return {.x = self.x + b.x, .y = self.y + b.y};
+    }
+    fn Scale[self: Point](v: i32) -> Point {
+      return {.x = self.x * v, .y = self.y * v};
+    }
+    fn Hold[self: Point](v: i32) -> Holder(i32) {
+      return {.v = v};
+    }
+  }
+}
+
+fn AddAndScaleGeneric[T:! AddMul, U:! Vector(T)](a: U, s: T) -> U {
+  return a.Add(U.Zero()).Scale(a.Hold(s).v);
+}
+
+fn Main() -> i32 {
+  var a: Point = {.x = 2, .y = 1};
+  var p: Point = AddAndScaleGeneric(a, 5);
+  return p.x - 10;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/7f48faf27fbcc85cce85d7d07d8557961e5ced8a b/toolchain/semantics/fuzzer_corpus/7f48faf27fbcc85cce85d7d07d8557961e5ced8a
new file mode 100644
index 000000000000..2f88e4cd4f83
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/7f48faf27fbcc85cce85d7d07d8557961e5ced8a
@@ -0,0 +1,17 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+interface IFace {
+  // CHECK:STDERR: COMPILATION ERROR: fail_use_assoc_const_before_decl.carbon:[[@LINE+1]]: 'C' has not been declared yet
+  let B:! C;
+  let C:! IFace;
+}
+
+fn Main() -> i32 {
+  // return T;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/7fb61b792562af16e1daf033786f58c7a823a070 b/toolchain/semantics/fuzzer_corpus/7fb61b792562af16e1daf033786f58c7a823a070
new file mode 100644
index 000000000000..7eb3b575d497
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/7fb61b792562af16e1daf033786f58c7a823a070
@@ -0,0 +1,12 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest library "Foo" api;
+
+fn Main() -> i32 {
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/7fb975bde1a7671c319af2ce9bb38f6aceba424a b/toolchain/semantics/fuzzer_corpus/7fb975bde1a7671c319af2ce9bb38f6aceba424a
new file mode 100644
index 000000000000..ddaba323920c
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/7fb975bde1a7671c319af2ce9bb38f6aceba424a
@@ -0,0 +1,14 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  var a: [i32;0] = ();
+  var b: [i32;] = a;
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/80d09b221ee7aa332626e27dd2a6a2bb32ce23f0 b/toolchain/semantics/fuzzer_corpus/80d09b221ee7aa332626e27dd2a6a2bb32ce23f0
new file mode 100644
index 000000000000..92779c95c32a
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/80d09b221ee7aa332626e27dd2a6a2bb32ce23f0
@@ -0,0 +1,13 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  // CHECK:STDERR: SYNTAX ERROR: fail_invalid_escape.carbon:[[@LINE+1]]: Invalid escaping in string: "str\e"
+  Print("str\e");
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/8190cd3b83ab71746ab0bd56f6d20bcd5bd1eb25 b/toolchain/semantics/fuzzer_corpus/8190cd3b83ab71746ab0bd56f6d20bcd5bd1eb25
new file mode 100644
index 000000000000..fef82e3fd2a6
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/8190cd3b83ab71746ab0bd56f6d20bcd5bd1eb25
@@ -0,0 +1,33 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+class Point {
+
+  fn Origin() -> Point {
+    return {.x = 0, .y = 0};
+  }
+
+  fn GetSetX[addr self: Point*](x: i32) -> i32 {
+    var old: auto = (*self).x;
+    (*self).x = x;
+    return old;
+  }
+
+  var x: i32;
+  var y: i32;
+}
+
+fn Main() -> i32 {
+  var p: Point = Point.Origin();
+  var x: auto = p.GetSetX(42);
+  if (p.x == 42) {
+    return x;
+  }
+  return 1;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/81c388f907f56f9cdea48326b67d8a4fa201c2c4 b/toolchain/semantics/fuzzer_corpus/81c388f907f56f9cdea48326b67d8a4fa201c2c4
new file mode 100644
index 000000000000..e8f4360fd6c3
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/81c388f907f56f9cdea48326b67d8a4fa201c2c4
@@ -0,0 +1,46 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: T as Iface
+// CHECK:STDOUT: T as Iface
+// CHECK:STDOUT: A as Iface
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+interface HasType {
+  let AssocType:! type;
+}
+
+interface Iface {
+  fn F();
+}
+
+impl forall [T:! HasType where .Self.AssocType impls Iface] T as Iface {
+  fn F() {
+    Print("T as Iface");
+    T.AssocType.(Iface.F)();
+  }
+}
+
+class A {
+  extend impl as Iface {
+    fn F() { Print("A as Iface"); }
+  }
+}
+
+class B {
+  extend impl as HasType where .AssocType = A {}
+}
+
+class C {
+  extend impl as HasType where .AssocType = B {}
+}
+
+fn Main() -> i32 {
+  let c: C = {};
+  c.(Iface.F)();
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/828812494bef26c4fc1629e0d0312f7b5d89f589 b/toolchain/semantics/fuzzer_corpus/828812494bef26c4fc1629e0d0312f7b5d89f589
new file mode 100644
index 000000000000..f49e04319da6
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/828812494bef26c4fc1629e0d0312f7b5d89f589
@@ -0,0 +1,14 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: 0: Heap{}
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  heap.PrintAllocs();
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/82eae3149f6f3f9fed1ae96957948932a119d9f5 b/toolchain/semantics/fuzzer_corpus/82eae3149f6f3f9fed1ae96957948932a119d9f5
new file mode 100644
index 000000000000..8daf4715bb32
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/82eae3149f6f3f9fed1ae96957948932a119d9f5
@@ -0,0 +1,23 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+class Point {
+  // Allowed: `Self` here means `Point`.
+  fn Origin() -> Self {
+    return {.x = 0, .y = 0};
+  }
+
+  var x: i32;
+  var y: i32;
+}
+
+fn Main() -> i32 {
+  var p: Point = Point.Origin();
+  return p.x;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/83941bf67b0cd2e4d3f7502b2bb40a83889bf78b b/toolchain/semantics/fuzzer_corpus/83941bf67b0cd2e4d3f7502b2bb40a83889bf78b
new file mode 100644
index 000000000000..93194c039a67
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/83941bf67b0cd2e4d3f7502b2bb40a83889bf78b
@@ -0,0 +1,10 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+// CHECK:STDERR: SYNTAX ERROR: fail_missing.carbon:[[@LINE+1]]: syntax error, unexpected FN, expecting PACKAGE
+fn Main() -> i32 {
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/839c2b2c711830a8a7a042ea58cf14f2da090add b/toolchain/semantics/fuzzer_corpus/839c2b2c711830a8a7a042ea58cf14f2da090add
new file mode 100644
index 000000000000..78ece4ebdde6
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/839c2b2c711830a8a7a042ea58cf14f2da090add
@@ -0,0 +1,21 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 3
+
+package ExplorerTest api;
+
+choice A {
+  Value(i32)
+}
+
+impl i32 as ImplicitAs(A) {
+  fn Convert[self: Self]() -> A { return A.Value(self + 1); }
+}
+
+fn Main() -> i32 {
+  let A.Value(n: i32) = 2;
+  return n;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/851814a8347766e5ac44e7674deda604717043ca b/toolchain/semantics/fuzzer_corpus/851814a8347766e5ac44e7674deda604717043ca
new file mode 100644
index 000000000000..3a0ac6346ad5
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/851814a8347766e5ac44e7674deda604717043ca
@@ -0,0 +1,20 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  if (0 == 0) {
+    if (0 == 1) {
+      return 1;
+    } else {
+      return 0;
+    }
+  }
+
+  return 1;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/852bf7ffb5136d7be49f858d8d73f8e2bb1936ce b/toolchain/semantics/fuzzer_corpus/852bf7ffb5136d7be49f858d8d73f8e2bb1936ce
new file mode 100644
index 000000000000..a47f197db9bd
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/852bf7ffb5136d7be49f858d8d73f8e2bb1936ce
@@ -0,0 +1,27 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: 5
+// CHECK:STDOUT: 4
+// CHECK:STDOUT: 0
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+class A { var n: i32; }
+
+impl A as BitAndWith(i32) where .Result = A {
+  fn Op[self: Self](rhs: i32) -> A { return {.n = self.n & rhs}; }
+}
+
+fn Main() -> i32 {
+  var a: A = {.n = 13};
+  a = a & 7;
+  Print("{0}", a.n);
+  a &= -2;
+  Print("{0}", a.n);
+  Print("{0}", (a & 3).n);
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/857f18630200f09d8fb028b8ccc4ce183a98c2cc b/toolchain/semantics/fuzzer_corpus/857f18630200f09d8fb028b8ccc4ce183a98c2cc
new file mode 100644
index 000000000000..46a22fb578f3
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/857f18630200f09d8fb028b8ccc4ce183a98c2cc
@@ -0,0 +1,43 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: (*c1).val: 1
+// CHECK:STDOUT: (*c2).val: 1
+// CHECK:STDOUT: (*d).val: 2
+// CHECK:STDOUT: e.val: 3
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+base class C {
+  var val: i32;
+}
+
+base class D {
+  extend base: C;
+  var val: i32;
+}
+
+class E {
+  extend base: D;
+  var val: i32;
+}
+
+fn Foo(c: C*) -> i32 {
+  return (*c).val;
+}
+
+fn Main() -> i32 {
+  var e: E = { .val = 3, .base = {.val = 2,.base = {.val = 1}}};
+  var d: D* = &e;
+  var c1: C* = &e;
+  var c2: C* = d;
+  Print("(*c1).val: {0}", (*c1).val);
+  Print("(*c2).val: {0}", (*c2).val);
+  Print("(*d).val: {0}", (*d).val);
+  Print("e.val: {0}", e.val);
+
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/85c4bfadcd8471f961da3bd10b0b34e4c7d5009f b/toolchain/semantics/fuzzer_corpus/85c4bfadcd8471f961da3bd10b0b34e4c7d5009f
new file mode 100644
index 000000000000..36079967ae07
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/85c4bfadcd8471f961da3bd10b0b34e4c7d5009f
@@ -0,0 +1,34 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+package ExplorerTest api;
+
+__mixin M1 {
+  fn F1[self: Self](x: Self) -> Self{
+     return x;
+  }
+  // CHECK:STDERR: COMPILATION ERROR: fail_circular_mixing.carbon:[[@LINE+1]]: 'M3' has not been declared yet
+  __mix M3;
+}
+
+__mixin M2 {
+  fn F2() {
+  }
+  __mix M1;
+}
+
+__mixin M3 {
+  __mix M2;
+  fn F3() {
+  }
+}
+
+class C {
+  __mix M2;
+}
+
+fn Main() -> i32 {
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/86a7b652e94c15d3bd45835b379bdbed8202f26c b/toolchain/semantics/fuzzer_corpus/86a7b652e94c15d3bd45835b379bdbed8202f26c
new file mode 100644
index 000000000000..9a3939c85955
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/86a7b652e94c15d3bd45835b379bdbed8202f26c
@@ -0,0 +1,20 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  var s: String = #'''
+    A "block" ""string"" literal
+      with indent.
+    '''#;
+  if (s == #"A \#"block\#" \#"\#"string\#"\#" literal\#n  with indent.\#n"#) {
+    return 0;
+  } else {
+    return 1;
+  }
+}
diff --git a/toolchain/semantics/fuzzer_corpus/87371229f1dd5b8a059f57ab0f6fba55e1221074 b/toolchain/semantics/fuzzer_corpus/87371229f1dd5b8a059f57ab0f6fba55e1221074
new file mode 100644
index 000000000000..514949218a9c
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/87371229f1dd5b8a059f57ab0f6fba55e1221074
@@ -0,0 +1,21 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: 1
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+fn Foo(n: i32) {
+  Print("{0}", n);
+}
+
+fn Main() -> i32 {
+  var v: {.a: i32, .b: i32} = {.a = 1, .b = 2};
+  let a: i32 = v.a;
+  v.b = 3;
+  Foo(a);
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/87ea823113de8af3e349558955a773c57f383e6d b/toolchain/semantics/fuzzer_corpus/87ea823113de8af3e349558955a773c57f383e6d
new file mode 100644
index 000000000000..11f97fef4e43
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/87ea823113de8af3e349558955a773c57f383e6d
@@ -0,0 +1,24 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 1
+
+package ExplorerTest api;
+
+interface A(T:! type) {}
+interface B {
+  fn F() -> i32;
+}
+
+class C(T:! type) {}
+
+impl forall [T:! type] C(T) as A(T) & B {
+  fn F() -> i32 { return 1; }
+}
+
+fn Main() -> i32 {
+  var v: C(i32) = {};
+  return v.(B.F)();
+}
diff --git a/toolchain/semantics/fuzzer_corpus/895bb8433ee2c3e9408e3d4f1979401d0bf4d064 b/toolchain/semantics/fuzzer_corpus/895bb8433ee2c3e9408e3d4f1979401d0bf4d064
new file mode 100644
index 000000000000..ab0e3dea94b9
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/895bb8433ee2c3e9408e3d4f1979401d0bf4d064
@@ -0,0 +1,20 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 7
+
+package ExplorerTest api;
+
+alias TypeAlias = i32;
+
+fn Function(a: i32, b: TypeAlias) -> i32 { return a + b; }
+fn GenericFunction[T:! type](x: T) -> T { return x; }
+
+alias FunctionAlias = Function;
+alias GenericFunctionAlias = GenericFunction;
+
+fn Main() -> i32 {
+  return FunctionAlias(1, 2) + GenericFunctionAlias(4);
+}
diff --git a/toolchain/semantics/fuzzer_corpus/8bb43cfab7a6921135707ad94afb8df7f34485c4 b/toolchain/semantics/fuzzer_corpus/8bb43cfab7a6921135707ad94afb8df7f34485c4
new file mode 100644
index 000000000000..2c6aee5f8036
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/8bb43cfab7a6921135707ad94afb8df7f34485c4
@@ -0,0 +1,13 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  // CHECK:STDERR: SYNTAX ERROR: fail_invalid_integer_type.carbon:[[@LINE+1]]: Invalid type literal: i11111111111111111111111111
+  var x: i11111111111111111111111111 = 1;
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/8e47cb329a5e2b86a17af1db4765dda7f4cb9522 b/toolchain/semantics/fuzzer_corpus/8e47cb329a5e2b86a17af1db4765dda7f4cb9522
new file mode 100644
index 000000000000..e4bf81001297
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/8e47cb329a5e2b86a17af1db4765dda7f4cb9522
@@ -0,0 +1,14 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+class C {
+  // CHECK:STDERR: SYNTAX ERROR: fail_method_self_misspelled.carbon:[[@LINE+1]]: illegal binding pattern in implicit parameter list
+  fn F[addr slef: Self*]() {}
+}
+
+fn Main() -> i32 { return 0; }
diff --git a/toolchain/semantics/fuzzer_corpus/8f084e14b32446d014b56c787cf20b5bcbcbf2b3 b/toolchain/semantics/fuzzer_corpus/8f084e14b32446d014b56c787cf20b5bcbcbf2b3
new file mode 100644
index 000000000000..5973806e0cf6
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/8f084e14b32446d014b56c787cf20b5bcbcbf2b3
@@ -0,0 +1,18 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+interface FrobWith(T:! type) {}
+
+fn F[T:! FrobWith(.Self)]
+  // CHECK:STDERR: COMPILATION ERROR: fail_dot_self_after_scope.carbon:[[@LINE+1]]: could not resolve '.Self'
+  (U: .Self) {
+}
+
+fn Main() -> i32 {
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/8f45cb7810622e3ea3355da118aa66bb05698c83 b/toolchain/semantics/fuzzer_corpus/8f45cb7810622e3ea3355da118aa66bb05698c83
new file mode 100644
index 000000000000..c7cd388898a5
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/8f45cb7810622e3ea3355da118aa66bb05698c83
@@ -0,0 +1,20 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  if (0 == 1) {
+    return 1;
+  } else if (0 == 2) {
+    return 2;
+  } else {
+    return 0;
+  }
+
+  return 1;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/8f5c05a54c77af530e9741b54ae4c04f578ce33f b/toolchain/semantics/fuzzer_corpus/8f5c05a54c77af530e9741b54ae4c04f578ce33f
new file mode 100644
index 000000000000..51d73f38b8d7
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/8f5c05a54c77af530e9741b54ae4c04f578ce33f
@@ -0,0 +1,16 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+// CHECK:STDERR: COMPILATION ERROR: fail_invalid_fnty.carbon:[[@LINE+2]]: type error in `-`:
+// CHECK:STDERR: could not find implementation of interface Negate for bool
+fn f(g: __Fn(-true) -> true) {
+}
+
+fn Main() -> i32 {
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/8f965c76081ac01748708ba9fe81fef86fc6ea47 b/toolchain/semantics/fuzzer_corpus/8f965c76081ac01748708ba9fe81fef86fc6ea47
new file mode 100644
index 000000000000..50a5de9585a1
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/8f965c76081ac01748708ba9fe81fef86fc6ea47
@@ -0,0 +1,16 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+fn swap[T:! type, U:! type](tuple: (T, U)) -> (U, T) {
+  return (tuple[1], tuple[0]);
+}
+
+fn Main() -> i32 {
+  return swap((0, true))[1];
+}
diff --git a/toolchain/semantics/fuzzer_corpus/8fe0b93d3fb32b620a168e162cede0cc51f98a21 b/toolchain/semantics/fuzzer_corpus/8fe0b93d3fb32b620a168e162cede0cc51f98a21
new file mode 100644
index 000000000000..c96255cfaa2c
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/8fe0b93d3fb32b620a168e162cede0cc51f98a21
@@ -0,0 +1,24 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+interface I {
+  fn G[self: Self]();
+}
+
+class C {
+  impl as I {
+    // CHECK:STDERR: COMPILATION ERROR: fail_impl_missing_self.carbon:[[@LINE+3]]: type error in member of implementation
+    // CHECK:STDERR: expected: fn [self: class C]() -> ()
+    // CHECK:STDERR: actual: fn () -> ()
+    fn G() { }
+  }
+}
+
+fn Main() -> i32 {
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/903677e98b215946f2feb75920c3f7f1bede77ff b/toolchain/semantics/fuzzer_corpus/903677e98b215946f2feb75920c3f7f1bede77ff
new file mode 100644
index 000000000000..02034f2e10a4
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/903677e98b215946f2feb75920c3f7f1bede77ff
@@ -0,0 +1,12 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+// CHECK:STDERR: COMPILATION ERROR: fail_dot_self_not_in_scope.carbon:[[@LINE+1]]: could not resolve '.Self'
+fn Main() -> .Self {
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/903eb115fd74cf5365d4a359caca9374cdd98d03 b/toolchain/semantics/fuzzer_corpus/903eb115fd74cf5365d4a359caca9374cdd98d03
new file mode 100644
index 000000000000..7549949d3721
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/903eb115fd74cf5365d4a359caca9374cdd98d03
@@ -0,0 +1,48 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+// Ensure that we can declare all different kinds of declarations as namespace
+// members.
+namespace N;
+
+__mixin N.Mixin {}
+
+base class N.BaseClass {
+  __mix Mixin;
+}
+
+class N.DerivedClass {
+  extend base: BaseClass;
+}
+
+namespace N.Inner;
+
+alias N.Inner.InnerClass = DerivedClass;
+
+choice N.Choice { A, B, C(DerivedClass) }
+
+interface N.Iface {
+  fn F() -> DerivedClass*;
+}
+
+constraint N.Constraint {
+  extend Iface;
+}
+
+var v: N.DerivedClass = {.base = {}};
+
+fn N.F[T:! Constraint]() {
+  var v: Inner.InnerClass = {.base = {}};
+}
+
+impl i32 as N.Constraint {
+  fn F() -> N.DerivedClass* { return &v; }
+}
+
+fn Main() -> i32 { return 0; }
diff --git a/toolchain/semantics/fuzzer_corpus/9291fb7d068a7b1191009b1f7225a7a6f1e4ad39 b/toolchain/semantics/fuzzer_corpus/9291fb7d068a7b1191009b1f7225a7a6f1e4ad39
new file mode 100644
index 000000000000..bf57d096226b
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/9291fb7d068a7b1191009b1f7225a7a6f1e4ad39
@@ -0,0 +1,88 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// This doesn't check trace output because it's too slow with it.
+// AUTOUPDATE
+// CHECK:STDOUT: result: 1
+
+package ExplorerTest api;
+
+interface ManyTypes {
+  let T0:! type;
+  let T1:! type;
+  let T2:! type;
+  let T3:! type;
+  let T4:! type;
+  let T5:! type;
+  let T6:! type;
+  let T7:! type;
+}
+
+interface Splat { fn Op(n: i32) -> Self; }
+impl i32 as Splat {
+  fn Op(n: i32) -> Self { return n; }
+}
+impl forall [T:! Splat] (T, T, T) as Splat {
+  fn Op(n: i32) -> Self {
+    let v: T = T.Op(n);
+    return (v, v, v);
+  }
+}
+
+fn CallSplat(T:! Splat, n: i32) -> T { return T.Op(n); }
+
+fn DoSplat(
+    M:! ManyTypes where
+      .T0 = (.T1, .T1, .T1) and
+      .T1 = (.T2, .T2, .T2) and
+      .T2 = (.T3, .T3, .T3) and
+      .T3 = (.T4, .T4, .T4) and
+      .T4 = (.T5, .T5, .T5) and
+      .T5 = (.T6, .T6, .T6) and
+      .T6 = (.T7, .T7, .T7) and
+      .T7 = i32,
+    n: M.T7) -> M.T0 {
+  return CallSplat(M.T0, n);
+}
+
+interface First { fn Op[self: Self]() -> i32; }
+impl i32 as First {
+  fn Op[self: Self]() -> i32 { return self; }
+}
+impl forall [T:! First] (T, T, T) as First {
+  fn Op[self: Self]() -> i32 {
+    let (a: T, b: T, c: T) = self;
+    return a.Op();
+  }
+}
+
+fn DoFirst(
+    M:! ManyTypes where
+      .T7 = i32 and
+      .T6 = (.T7, .T7, .T7) and
+      .T5 = (.T6, .T6, .T6) and
+      .T4 = (.T5, .T5, .T5) and
+      .T3 = (.T4, .T4, .T4) and
+      .T2 = (.T3, .T3, .T3) and
+      .T1 = (.T2, .T2, .T2) and
+      .T0 = (.T1, .T1, .T1),
+    v: M.T0) -> M.T7 {
+  return v.(First.Op)();
+}
+
+class C {
+  extend impl as ManyTypes where
+      .T3 = (.T4, .T4, .T4) and
+      .T1 = (.T2, .T2, .T2) and
+      .T4 = (.T5, .T5, .T5) and
+      .T6 = (.T7, .T7, .T7) and
+      .T2 = (.T3, .T3, .T3) and
+      .T7 = i32 and
+      .T5 = (.T6, .T6, .T6) and
+      .T0 = (.T1, .T1, .T1) {}
+}
+
+fn Main() -> i32 {
+  return DoFirst(C, DoSplat(C, 1));
+}
diff --git a/toolchain/semantics/fuzzer_corpus/9376518e1dc8f99232774ebfed8bd2ec067c57bb b/toolchain/semantics/fuzzer_corpus/9376518e1dc8f99232774ebfed8bd2ec067c57bb
new file mode 100644
index 000000000000..45a45711100f
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/9376518e1dc8f99232774ebfed8bd2ec067c57bb
@@ -0,0 +1,20 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+interface GetX {
+  fn DoIt[self: Self]() -> i32;
+}
+
+impl forall [template T:! type] T as GetX {
+  // CHECK:STDERR: COMPILATION ERROR: fail_no_member.carbon:[[@LINE+1]]: member access, unexpected i32 in self.x
+  fn DoIt[self: Self]() -> i32 { return self.x; }
+}
+
+fn Main() -> i32 {
+  return 0.(GetX.DoIt)();
+}
diff --git a/toolchain/semantics/fuzzer_corpus/93fb896d84d3c28400848dd05e02196ca359693f b/toolchain/semantics/fuzzer_corpus/93fb896d84d3c28400848dd05e02196ca359693f
new file mode 100644
index 000000000000..dbeaac11b776
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/93fb896d84d3c28400848dd05e02196ca359693f
@@ -0,0 +1,16 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+fn f(x: i32, y: i32) -> i32 { return x + y; }
+
+fn Main() -> i32 {
+  var xy: (i32, i32) = (1, 2);
+  // should fail to type-check
+  // CHECK:STDERR: COMPILATION ERROR: fail_call_with_tuple.carbon:[[@LINE+1]]: wrong number of arguments in function call, expected 2 but got 1
+  return f(xy);
+}
diff --git a/toolchain/semantics/fuzzer_corpus/93fb94869ce61d6f894145f00e041f6ba3bc4219 b/toolchain/semantics/fuzzer_corpus/93fb94869ce61d6f894145f00e041f6ba3bc4219
new file mode 100644
index 000000000000..30c171caa3ef
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/93fb94869ce61d6f894145f00e041f6ba3bc4219
@@ -0,0 +1,27 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: 4
+// CHECK:STDOUT: 3
+// CHECK:STDOUT: 2
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+class A { var n: i32; }
+
+impl A as SubWith(i32) where .Result = A {
+  fn Op[self: Self](rhs: i32) -> A { return {.n = self.n - rhs}; }
+}
+
+fn Main() -> i32 {
+  var a: A = {.n = 5};
+  a = a - 1;
+  Print("{0}", a.n);
+  a -= 1;
+  Print("{0}", a.n);
+  Print("{0}", (a - 1).n);
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/94042b6c90ab6c8991a69696ef27dd8360fc4a97 b/toolchain/semantics/fuzzer_corpus/94042b6c90ab6c8991a69696ef27dd8360fc4a97
new file mode 100644
index 000000000000..6cb15e5f3d14
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/94042b6c90ab6c8991a69696ef27dd8360fc4a97
@@ -0,0 +1,13 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  var (x: auto, y: auto) = (2, 3);
+  return y - x - 1;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/94e81fee5787c7d7cbc11d9bb6d6a42f1fa1fd3f b/toolchain/semantics/fuzzer_corpus/94e81fee5787c7d7cbc11d9bb6d6a42f1fa1fd3f
new file mode 100644
index 000000000000..9a905a6e6b44
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/94e81fee5787c7d7cbc11d9bb6d6a42f1fa1fd3f
@@ -0,0 +1,16 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// TODO: This SHOULD fail but doesn't presently.
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+import ExplorerTest library "Nonexistent";
+
+fn Main() -> i32 {
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/9508a414e54a420c8f31afaba22d8894f8cbf5e3 b/toolchain/semantics/fuzzer_corpus/9508a414e54a420c8f31afaba22d8894f8cbf5e3
new file mode 100644
index 000000000000..b4f406503629
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/9508a414e54a420c8f31afaba22d8894f8cbf5e3
@@ -0,0 +1,19 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+fn CompareStr(s: String) -> i32 {
+  if (s == ##"#"str"#"##) {
+    return 0;
+  }
+  return 1;
+}
+
+fn Main() -> i32 {
+  return CompareStr("#\"str\"#");
+}
diff --git a/toolchain/semantics/fuzzer_corpus/954bef329801d815ea7fc44588cb5f6d741104d7 b/toolchain/semantics/fuzzer_corpus/954bef329801d815ea7fc44588cb5f6d741104d7
new file mode 100644
index 000000000000..022805bab42c
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/954bef329801d815ea7fc44588cb5f6d741104d7
@@ -0,0 +1,21 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+class Point {
+  fn Origin() -> Point {
+    return {.x = 0, .y = 0};
+  }
+  var x: i32;
+  var y: i32;
+}
+
+fn Main() -> i32 {
+  // CHECK:STDERR: COMPILATION ERROR: fail_instantiate_non_generic.carbon:[[@LINE+1]]: in call `Point(i32)`, expected callee to be a function, found `type`
+  var p: Point(i32) = Point.Origin();
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/95eaba17106b051bb2ec04c8ce3a48373ed238c0 b/toolchain/semantics/fuzzer_corpus/95eaba17106b051bb2ec04c8ce3a48373ed238c0
new file mode 100644
index 000000000000..c778eb7b6ab9
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/95eaba17106b051bb2ec04c8ce3a48373ed238c0
@@ -0,0 +1,25 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 3
+
+package Foo api;
+interface A {
+  fn F[self: Self](o: Self) -> Self;
+}
+class X {
+  extend impl as A {
+    fn F[self: Self](o: Self) -> Self { return {.n = self.n + o.n}; }
+  }
+  var n: i32;
+}
+fn F[T:! A](v: T, w: T) -> T {
+  return v.(T.(A.F))(w);
+}
+fn Main() -> i32 {
+  var v: X = {.n = 1};
+  var w: X = {.n = 2};
+  return F(v, w).n;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/9616f0607e0aa53f32551c7cf3fc08efa7e7fb86 b/toolchain/semantics/fuzzer_corpus/9616f0607e0aa53f32551c7cf3fc08efa7e7fb86
new file mode 100644
index 000000000000..372703f44228
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/9616f0607e0aa53f32551c7cf3fc08efa7e7fb86
@@ -0,0 +1,15 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+// This declaration is not allowed.
+// CHECK:STDERR: COMPILATION ERROR: fail_separate_decl.carbon:[[@LINE+1]]: Function declaration has deduced return type but no body
+fn ComputeSum(x: i32, y: i32) -> auto;
+
+fn Main() -> i32 {
+  return ComputeSum(1, 2) - 3;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/97dd9ece505acb1475a24cff9ac3f30762854b56 b/toolchain/semantics/fuzzer_corpus/97dd9ece505acb1475a24cff9ac3f30762854b56
new file mode 100644
index 000000000000..455bd1c49743
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/97dd9ece505acb1475a24cff9ac3f30762854b56
@@ -0,0 +1,33 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+class S(T:! type) {}
+class Z {}
+
+class Tree(L:! type, R:! type) {}
+class Leaf {}
+
+interface Foo(T:! type) {}
+
+impl forall [U:! type, T:! Foo(Tree(U, U))] S(T) as Foo(U) {}
+
+alias Level1 = Tree(Leaf, Leaf);
+alias Level2 = Tree(Level1, Level1);
+alias Level3 = Tree(Level2, Level2);
+alias Level4 = Tree(Level3, Level3);
+alias Level5 = Tree(Level4, Level4);
+
+impl Z as Foo(Level5) {}
+
+fn F[T:! Foo(Leaf)](x: T) {}
+fn Main() -> i32 {
+  var n: S(S(S(S(S(Z))))) = {};
+  F(n);
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/9898ec32a1d2cd6911f4815a43178aa358d49458 b/toolchain/semantics/fuzzer_corpus/9898ec32a1d2cd6911f4815a43178aa358d49458
new file mode 100644
index 000000000000..113937a5a6d6
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/9898ec32a1d2cd6911f4815a43178aa358d49458
@@ -0,0 +1,13 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  var t: (auto, (i32, i32)) = ((1, 2), (3, 4));
+  return t[0][0] + t[1][1] - 5;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/996146c52ec6d4b88e1a5c6f2ad1f8a8ed23a2a0 b/toolchain/semantics/fuzzer_corpus/996146c52ec6d4b88e1a5c6f2ad1f8a8ed23a2a0
new file mode 100644
index 000000000000..8f88632aa464
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/996146c52ec6d4b88e1a5c6f2ad1f8a8ed23a2a0
@@ -0,0 +1,27 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+class Point {
+  fn Origin() -> Point {
+    return {.x = 0, .y = 0};
+  }
+
+  // Allowed: `Self` here means `Point`.
+  fn GetX[self: Self]() -> i32 {
+    return self.x;
+  }
+
+  var x: i32;
+  var y: i32;
+}
+
+fn Main() -> i32 {
+  var p: Point = Point.Origin();
+  return p.GetX();
+}
diff --git a/toolchain/semantics/fuzzer_corpus/99e29fe8751a2b381ff98f6a7f8fd5a39f47a089 b/toolchain/semantics/fuzzer_corpus/99e29fe8751a2b381ff98f6a7f8fd5a39f47a089
new file mode 100644
index 000000000000..e85d200c0182
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/99e29fe8751a2b381ff98f6a7f8fd5a39f47a089
@@ -0,0 +1,13 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  // CHECK:STDERR: COMPILATION ERROR: fail_length_mismatch_with_auto.carbon:[[@LINE+1]]: tuples of different length
+  var a: (auto,) = (1, 2);
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/9a93b28a17b3037de343c7627970a21ea9f36ad6 b/toolchain/semantics/fuzzer_corpus/9a93b28a17b3037de343c7627970a21ea9f36ad6
new file mode 100644
index 000000000000..181d401a183c
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/9a93b28a17b3037de343c7627970a21ea9f36ad6
@@ -0,0 +1,19 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+class Point(T:! type) {
+  var x: T;
+  var y: T;
+}
+
+fn Main() -> i32 {
+  var p: Point(i32) = {.x = 0, .y = 0};
+  // CHECK:STDERR: COMPILATION ERROR: fail_point_equal.carbon:[[@LINE+1]]: type error in initializer of variable: 'class Point(T = i32)' is not implicitly convertible to 'class Point(T = bool)'
+  var q: Point(bool) = p;
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/9be6536b748480b8d7046c4e360fefa33a996d59 b/toolchain/semantics/fuzzer_corpus/9be6536b748480b8d7046c4e360fefa33a996d59
new file mode 100644
index 000000000000..653272ad868d
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/9be6536b748480b8d7046c4e360fefa33a996d59
@@ -0,0 +1,14 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+interface Invalid {}
+
+fn Main() -> i32 {
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/9c8bddc13ecba23e290de63fec0c6ae8514e9ae4 b/toolchain/semantics/fuzzer_corpus/9c8bddc13ecba23e290de63fec0c6ae8514e9ae4
new file mode 100644
index 000000000000..031a7f3573a0
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/9c8bddc13ecba23e290de63fec0c6ae8514e9ae4
@@ -0,0 +1,54 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: H 22
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+
+choice MyOptionalElement(T:! type) {
+  None(),
+  Element(T)
+}
+
+class MyOptional(T:! type){
+   fn CreateEmpty() -> MyOptional(T){
+       return { .element = MyOptionalElement(T).None() };
+   }
+   fn Create ( value: T ) -> MyOptional(T){
+       return { .element = MyOptionalElement(T).Element(value) };
+   }
+
+    fn has_value[self: Self] () -> bool{
+        var x: MyOptionalElement(T) = self.element;
+        match(x){
+            case MyOptionalElement(T).None() => { return false; }
+        }
+        return false;
+    }
+
+    fn get[self: Self] () -> T {
+        var x: MyOptionalElement(T) = self.element;
+        match(x){
+            case MyOptionalElement(T).Element( var x: T ) =>{
+                return x;
+            }
+        }
+        // TODO: Mark this as unreachable somehow.
+        return get();
+    }
+
+   var element: MyOptionalElement(T);
+}
+
+
+fn Main() -> i32 {
+  var f: MyOptional(i32) = MyOptional(i32).Create(22);
+  var x: i32 = f.get();
+  Print("H {0}",x);
+
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/9d3ad28603113f1a195ef1ff6d7df7acb28fb605 b/toolchain/semantics/fuzzer_corpus/9d3ad28603113f1a195ef1ff6d7df7acb28fb605
new file mode 100644
index 000000000000..823c8f52f688
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/9d3ad28603113f1a195ef1ff6d7df7acb28fb605
@@ -0,0 +1,39 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: DESTRUCTOR C 1
+// CHECK:STDOUT: DESTRUCTOR B 2
+// CHECK:STDOUT: DESTRUCTOR A 3
+// CHECK:STDOUT: result: 1
+
+package ExplorerTest api;
+
+class A{
+    destructor[self: Self]{
+        Print("DESTRUCTOR A {0}",self.n);
+    }
+    var n: i32;
+}
+
+class B{
+    destructor[self: Self]{
+        Print("DESTRUCTOR B {0}",self.n);
+    }
+    var n: i32;
+}
+
+class C{
+    destructor[self: Self]{
+        Print("DESTRUCTOR C {0}",self.n);
+    }
+    var n: i32;
+}
+
+fn Main() -> i32 {
+  var a: A = {.n = 3};
+  var b: B = {.n = 2};
+  var c: C = {.n = 1};
+  return 1;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/9e094e36792e0aaecca1ff9a71578e9d30acd809 b/toolchain/semantics/fuzzer_corpus/9e094e36792e0aaecca1ff9a71578e9d30acd809
new file mode 100644
index 000000000000..9b902358dbc9
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/9e094e36792e0aaecca1ff9a71578e9d30acd809
@@ -0,0 +1,36 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 25
+
+package ExplorerTest api;
+
+class List {
+  choice Node {
+    Nil,
+    Cons(i32, Self*)
+  }
+  var node: Node;
+
+  // Creates a list of `Cons(n, Cons(n - 1, ... Cons(1, Nil) ... ))`.
+  fn Make(n: i32) -> Self {
+    return {
+      .node = if n == 0 then Node.Nil else Node.Cons(n, heap.New(Make(n - 1)))
+    };
+  }
+
+  // Returns the sum of values in the list plus the value of `a`.
+  fn Sum[self: Self](a: i32) -> i32 {
+    match (self.node) {
+      case Node.Nil => { return a; }
+      case Node.Cons(b: i32, rest: Self*) => { return rest->Sum(a + b); }
+    }
+  }
+}
+
+fn Main() -> i32 {
+  var l: List = List.Make(5);
+  return l.Sum(10);
+}
diff --git a/toolchain/semantics/fuzzer_corpus/9ef0d30288fa7ec2d26c89a11fca1aafa1ffe7c9 b/toolchain/semantics/fuzzer_corpus/9ef0d30288fa7ec2d26c89a11fca1aafa1ffe7c9
new file mode 100644
index 000000000000..30f39b6dc59d
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/9ef0d30288fa7ec2d26c89a11fca1aafa1ffe7c9
@@ -0,0 +1,13 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  var x: i32 = 0;
+  return x;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/9f448813378568e8b33edac8f46e3e419cc936cc b/toolchain/semantics/fuzzer_corpus/9f448813378568e8b33edac8f46e3e419cc936cc
new file mode 100644
index 000000000000..d43ef6ca66eb
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/9f448813378568e8b33edac8f46e3e419cc936cc
@@ -0,0 +1,25 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+class Point {
+  fn Origin() -> Point {
+    return {.x = 0, .y = 0};
+  }
+  fn GetX[self: Point]() -> i32 {
+    return self.x;
+  }
+  var x: i32;
+  var y: i32;
+}
+
+fn Main() -> i32 {
+  var p: Point = Point.Origin();
+  var f: __Fn() -> i32 = p.GetX;
+  return f();
+}
diff --git a/toolchain/semantics/fuzzer_corpus/9f451f15c28166724e9389efbc97cd00c5f362a4 b/toolchain/semantics/fuzzer_corpus/9f451f15c28166724e9389efbc97cd00c5f362a4
new file mode 100644
index 000000000000..aa3905ca0255
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/9f451f15c28166724e9389efbc97cd00c5f362a4
@@ -0,0 +1,14 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  var x: i32;
+  // CHECK:STDERR: COMPILATION ERROR: fail_increment.carbon:[[@LINE+1]]: use of uninitialized variable x
+  ++x;
+  return x;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/9f5970dd9c7258c0b821fd5ae34567d74212ba97 b/toolchain/semantics/fuzzer_corpus/9f5970dd9c7258c0b821fd5ae34567d74212ba97
new file mode 100644
index 000000000000..22bb572a3b58
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/9f5970dd9c7258c0b821fd5ae34567d74212ba97
@@ -0,0 +1,13 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDERR: RUNTIME ERROR: {{.*}}/explorer/data/prelude.carbon:{{.*}}: Integer overflow
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  var a: auto = 5 >> 75;
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/9fb1f522bd3e58d4e328258b44317fb30a97fc1c b/toolchain/semantics/fuzzer_corpus/9fb1f522bd3e58d4e328258b44317fb30a97fc1c
new file mode 100644
index 000000000000..3929f5bb3562
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/9fb1f522bd3e58d4e328258b44317fb30a97fc1c
@@ -0,0 +1,31 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+// The bodies of member functions are processed after all immediately enclosing
+// classes, impl declarations, and interfaces.
+class A {
+  fn F() -> type {
+    return i32;
+  }
+  // OK, resolves to `A.F`.
+  fn G() -> F() {
+    return 0;
+  }
+
+  // CHECK:STDERR: COMPILATION ERROR: fail_class_fn_use_before_declaration.carbon:[[@LINE+1]]: 'I' has not been declared yet
+  fn H() -> I() {
+    return 0;
+  }
+  fn I() -> type {
+    return i32;
+  }
+}
+
+fn Main() -> i32 {
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/a011088c7e451b85fecd399382733c73f802f28a b/toolchain/semantics/fuzzer_corpus/a011088c7e451b85fecd399382733c73f802f28a
new file mode 100644
index 000000000000..5f8733bd9a74
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/a011088c7e451b85fecd399382733c73f802f28a
@@ -0,0 +1,28 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: DESTRUCTOR A 1
+// CHECK:STDOUT: DESTRUCTOR A 2
+// CHECK:STDOUT: DESTRUCTOR A 3
+// CHECK:STDOUT: DESTRUCTOR A 4
+// CHECK:STDOUT: DESTRUCTOR A 5
+// CHECK:STDOUT: DESTRUCTOR A 6
+// CHECK:STDOUT: result: 1
+
+package ExplorerTest api;
+
+
+class A{
+    destructor[self: Self]{
+        Print("DESTRUCTOR A {0}",self.n);
+    }
+    var n: i32;
+}
+
+fn Main() -> i32 {
+  var a: [A; 2] = ({.n = 6},{.n = 5});
+  var b: [[A; 2]; 2] = (({.n = 4},{.n = 3}), ({.n = 2},{.n = 1}));
+  return 1;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/a01c8bc05abec666a02db1ab14935e847cef45d6 b/toolchain/semantics/fuzzer_corpus/a01c8bc05abec666a02db1ab14935e847cef45d6
new file mode 100644
index 000000000000..aec7e67f2509
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/a01c8bc05abec666a02db1ab14935e847cef45d6
@@ -0,0 +1,17 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  // -2147483648 is unsupported as a literal, but we can do it with a decrement.
+  var low: i32 = -2147483647;
+  low -= 1;
+  var high: i32 = 2147483647;
+  Rand(low, high);
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/a34128de7c6b4324037a1d26386e5712188b6598 b/toolchain/semantics/fuzzer_corpus/a34128de7c6b4324037a1d26386e5712188b6598
new file mode 100644
index 000000000000..9e7600afd376
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/a34128de7c6b4324037a1d26386e5712188b6598
@@ -0,0 +1,52 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+fn identFn( x: i32 ) -> i32{
+    return x;
+}
+
+fn Main() -> i32 {
+  var x : i32 = 7 % 2;
+
+
+  if(  x != 1){
+      return 1;
+  }
+  x = (3*3) % 3;
+  if( x != 0){
+      return 2;
+  }
+
+  x = (4+4+4+4) % (2+1);
+  if(  x != 1){
+      return 3;
+  }
+
+  x = 15 % (identFn(2)+1);
+  if( x != 0){
+      return 4;
+  }
+
+  x = -15 % 7;
+  if( x != -1){
+      return 5;
+  }
+
+  x = 15 % -7;
+  if(  x != 1){
+      return 6;
+  }
+
+  x = -15 % -identFn(7);
+  if( x != -1){
+      return 7;
+  }
+
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/a3a77b1b81f7a7ed4bfacadef7c9e26e94215d67 b/toolchain/semantics/fuzzer_corpus/a3a77b1b81f7a7ed4bfacadef7c9e26e94215d67
new file mode 100644
index 000000000000..87b7f8b0381b
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/a3a77b1b81f7a7ed4bfacadef7c9e26e94215d67
@@ -0,0 +1,13 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  // CHECK:STDERR: SYNTAX ERROR: fail_tab.carbon:[[@LINE+1]]: Invalid escaping in string: "new	line"
+  Print("new	line");
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/a3bccd84f98029e5646785b746d7060e05b94a67 b/toolchain/semantics/fuzzer_corpus/a3bccd84f98029e5646785b746d7060e05b94a67
new file mode 100644
index 000000000000..285ea47d6e6c
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/a3bccd84f98029e5646785b746d7060e05b94a67
@@ -0,0 +1,12 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+fn CompareBools(a: bool, b: bool) -> bool {
+  // CHECK:STDERR: SYNTAX ERROR: fail_compare_precedence.carbon:[[@LINE+1]]: syntax error, unexpected EQUAL_EQUAL, expecting SEMICOLON
+  return not a == b;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/a3c0fbd0181c8c492babc4d2f43c63c172c7ee9a b/toolchain/semantics/fuzzer_corpus/a3c0fbd0181c8c492babc4d2f43c63c172c7ee9a
new file mode 100644
index 000000000000..e572e568f077
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/a3c0fbd0181c8c492babc4d2f43c63c172c7ee9a
@@ -0,0 +1,19 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: Interface: -3
+// CHECK:STDOUT: Op: -3
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  var val: i32 = 3;
+  // Make sure that both the interface and operator work with i32. These rely on
+  // builtin arithmetic more directly.
+  Print("Interface: {0}", val.(Negate.Op)());
+  Print("Op: {0}", -val);
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/a3e02430dc2657bec82d5c18ed4443701f8014d1 b/toolchain/semantics/fuzzer_corpus/a3e02430dc2657bec82d5c18ed4443701f8014d1
new file mode 100644
index 000000000000..cb952f94adc2
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/a3e02430dc2657bec82d5c18ed4443701f8014d1
@@ -0,0 +1,12 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  // CHECK:STDERR: COMPILATION ERROR: fail_unimplemented_example.carbon:[[@LINE+1]]: Unimplemented
+  return 1 __unimplemented_example_infix 2;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/a418c18490f25bad7569608825bb2cfc65010510 b/toolchain/semantics/fuzzer_corpus/a418c18490f25bad7569608825bb2cfc65010510
new file mode 100644
index 000000000000..42ca0afa4df2
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/a418c18490f25bad7569608825bb2cfc65010510
@@ -0,0 +1,24 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: -2
+
+package ExplorerTest api;
+
+fn apply[T:! type, U:! type](f: __Fn (T) -> U, x: T) -> U {
+  return f(x);
+}
+
+fn positive(x: bool) -> i32 {
+  if (x) {
+    return 2;
+  } else {
+    return -2;
+  }
+}
+
+fn Main() -> i32 {
+  return apply(positive, false);
+}
diff --git a/toolchain/semantics/fuzzer_corpus/a46860eeff8a4a87f40c22b291dd4682ff578c79 b/toolchain/semantics/fuzzer_corpus/a46860eeff8a4a87f40c22b291dd4682ff578c79
new file mode 100644
index 000000000000..e3cc249967a4
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/a46860eeff8a4a87f40c22b291dd4682ff578c79
@@ -0,0 +1,16 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  var x: auto = {.x = 10, .y = 1};
+  var p: i32* = &x.x;
+  *p = 0;
+
+  return x.x;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/a470239a151b81273a143b8a350a3af05e527438 b/toolchain/semantics/fuzzer_corpus/a470239a151b81273a143b8a350a3af05e527438
new file mode 100644
index 000000000000..fa9ea83a7f25
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/a470239a151b81273a143b8a350a3af05e527438
@@ -0,0 +1,17 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  var a: i32 = 1;
+  let a_pinned: i32 = a;
+  let a_pinned2: i32 = a;
+  // OK: Value unused after being mutated.
+  a = 2;
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/a4e9de3300c2b7abcb4de7496fef8fe9c1b3c4e3 b/toolchain/semantics/fuzzer_corpus/a4e9de3300c2b7abcb4de7496fef8fe9c1b3c4e3
new file mode 100644
index 000000000000..c072ef7d303b
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/a4e9de3300c2b7abcb4de7496fef8fe9c1b3c4e3
@@ -0,0 +1,17 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+// Test multiple arguments
+fn f(x: i32, y: i32) -> i32 {
+  return x + y;
+}
+
+fn Main() -> i32 {
+  return f(2, 3) - 5;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/a5a01595fd372c8eeb51411f91438e859a976275 b/toolchain/semantics/fuzzer_corpus/a5a01595fd372c8eeb51411f91438e859a976275
new file mode 100644
index 000000000000..f6cdf2b263c0
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/a5a01595fd372c8eeb51411f91438e859a976275
@@ -0,0 +1,19 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+// Error: Can't use keyword `Self` as the name of a class.
+// CHECK:STDERR: SYNTAX ERROR: fail_class_named_self.carbon:[[@LINE+1]]: syntax error, unexpected SELF, expecting identifier or LEFT_PARENTHESIS
+class Self {
+  var x: i32;
+  var y: i32;
+}
+
+fn Main() -> i32 {
+  var p: Self = {.x = 1, .y = 2};
+  return p.y - p.x - 1;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/a8a0c6ffc4cd6d63b08501b9166737fe0e02c79d b/toolchain/semantics/fuzzer_corpus/a8a0c6ffc4cd6d63b08501b9166737fe0e02c79d
new file mode 100644
index 000000000000..38c21f708184
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/a8a0c6ffc4cd6d63b08501b9166737fe0e02c79d
@@ -0,0 +1,35 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+interface Number {
+  fn Zero() -> Self;
+  fn Add[self: Self](other: Self) -> Self;
+}
+
+class Point(T:! Number) {
+  fn Origin() -> Point(T) {
+    return {.x = T.Zero(), .y = T.Zero()};
+  }
+  var x: T;
+  var y: T;
+}
+
+impl i32 as Number {
+  fn Zero() -> i32 { return 0; }
+  fn Add[self: i32](other: i32) -> i32 { return self + other; }
+}
+
+fn SumXY[U:! Number](p: Point(U)) -> U {
+  return p.Origin().x.Add(p.y);
+}
+
+fn Main() -> i32 {
+  var p: Point(i32) = {.x = 0, .y = 0};
+  return SumXY(p);
+}
diff --git a/toolchain/semantics/fuzzer_corpus/a8dd59ebd4d67161627fc37cf42f56266eee84cc b/toolchain/semantics/fuzzer_corpus/a8dd59ebd4d67161627fc37cf42f56266eee84cc
new file mode 100644
index 000000000000..a633b93c87ce
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/a8dd59ebd4d67161627fc37cf42f56266eee84cc
@@ -0,0 +1,16 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  var arr: [i32; 2] = (0, 1);
+  var x: [i32;] = arr;
+  var index: i32 = 1;
+  x[index] = 0;
+  return x[0] + x[1];
+}
diff --git a/toolchain/semantics/fuzzer_corpus/aa886554975dd8babdee871ba3a36cfdbf09adde b/toolchain/semantics/fuzzer_corpus/aa886554975dd8babdee871ba3a36cfdbf09adde
new file mode 100644
index 000000000000..ee875ff50c93
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/aa886554975dd8babdee871ba3a36cfdbf09adde
@@ -0,0 +1,20 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: Destructor
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+class C {
+  destructor[self: Self] {
+    Print("Destructor");
+  }
+}
+
+fn Main() -> i32 {
+  let c: C = {};
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/aa9139a5f1e7ae6867692e648fbfad717185399b b/toolchain/semantics/fuzzer_corpus/aa9139a5f1e7ae6867692e648fbfad717185399b
new file mode 100644
index 000000000000..6369363bdba3
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/aa9139a5f1e7ae6867692e648fbfad717185399b
@@ -0,0 +1,16 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+interface Interface {}
+impl {} as Interface {}
+impl {.x: i32} as Interface {}
+
+fn Main() -> i32 {
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/aabd223c584f5f94b59f397f0b60e428ef3467b4 b/toolchain/semantics/fuzzer_corpus/aabd223c584f5f94b59f397f0b60e428ef3467b4
new file mode 100644
index 000000000000..cef5dce79312
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/aabd223c584f5f94b59f397f0b60e428ef3467b4
@@ -0,0 +1,74 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: Struct OK
+// CHECK:STDOUT: Choice OK
+// CHECK:STDOUT: Class OK
+// CHECK:STDOUT: Interface OK
+// CHECK:STDOUT: Constraint OK
+// CHECK:STDOUT: result: 0
+
+package Foo api;
+
+choice Choice { Alternative() }
+class Class { fn F(n: i32) -> i32 { return n + 1; } }
+interface Interface { fn G[self: Self]() -> Self; }
+interface AnotherInterface {}
+
+impl i32 as Interface { fn G[self: i32]() -> i32 { return self + 1; } }
+impl i32 as AnotherInterface {}
+
+// TODO: These are intended to be called at compile time. Mark them as
+// constexpr once we have syntax for that.
+fn GetStruct() -> type { return {.n: i32}; }
+fn GetChoice() -> type { return Choice; }
+fn GetClass() -> type { return Class; }
+fn GetInterface() -> type { return Interface; }
+fn GetConstraint() -> type { return Interface & AnotherInterface; }
+
+fn TestStruct() {
+  var s: GetStruct() = {.n = 1};
+  if (s.(GetStruct().n) == 1) {
+    Print("Struct OK");
+  }
+}
+
+fn TestChoice() {
+  var c: GetChoice() = GetChoice().Alternative();
+  match (c) {
+    case GetChoice().Alternative() => {
+      Print("Choice OK");
+    }
+  }
+}
+
+fn TestClass() {
+  if (GetClass().F(1) == 2) {
+    Print("Class OK");
+  }
+}
+
+fn TestInterface() {
+  var n: i32 = 1;
+  if (n.(GetInterface().G)() == 2) {
+    Print("Interface OK");
+  }
+}
+
+fn TestConstraint() {
+  var n: i32 = 1;
+  if (n.(GetConstraint().G)() == 2) {
+    Print("Constraint OK");
+  }
+}
+
+fn Main() -> i32 {
+  TestStruct();
+  TestChoice();
+  TestClass();
+  TestInterface();
+  TestConstraint();
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/ab552ac377163a3e30372abf70dce002ad1e3504 b/toolchain/semantics/fuzzer_corpus/ab552ac377163a3e30372abf70dce002ad1e3504
new file mode 100644
index 000000000000..b974b16b930d
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/ab552ac377163a3e30372abf70dce002ad1e3504
@@ -0,0 +1,12 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest impl;
+
+fn Main() -> i32 {
+  // CHECK:STDERR: COMPILATION ERROR: fail_intrinsic_too_many_args.carbon:[[@LINE+1]]: Print takes 1 or 2 arguments, received 4
+  __intrinsic_print("", 1, 2, 3);
+}
diff --git a/toolchain/semantics/fuzzer_corpus/ac402eca16b8a60ca297a1c22e20896e4ac13d0c b/toolchain/semantics/fuzzer_corpus/ac402eca16b8a60ca297a1c22e20896e4ac13d0c
new file mode 100644
index 000000000000..2c523f4f264a
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/ac402eca16b8a60ca297a1c22e20896e4ac13d0c
@@ -0,0 +1,28 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: strings less: 1
+// CHECK:STDOUT: ints less: 0
+// CHECK:STDOUT: strings less eq: 1
+// CHECK:STDOUT: ints less eq: 1
+// CHECK:STDOUT: strings greater: 0
+// CHECK:STDOUT: ints greater: 0
+// CHECK:STDOUT: strings greater eq: 0
+// CHECK:STDOUT: ints greater eq: 1
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  Print("strings less: {0}", if "hello" < "world" then 1 else 0);
+  Print("ints less: {0}", if 1 < 1 then 1 else 0);
+  Print("strings less eq: {0}", if "hello" <= "world" then 1 else 0);
+  Print("ints less eq: {0}", if 1 <= 1 then 1 else 0);
+  Print("strings greater: {0}", if "hello" > "world" then 1 else 0);
+  Print("ints greater: {0}", if 1 > 1 then 1 else 0);
+  Print("strings greater eq: {0}", if "hello" >= "world" then 1 else 0);
+  Print("ints greater eq: {0}", if 1 >= 1 then 1 else 0);
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/acc010e81f0b5de102362c90fb118a5b56e2c25e b/toolchain/semantics/fuzzer_corpus/acc010e81f0b5de102362c90fb118a5b56e2c25e
new file mode 100644
index 000000000000..cf599fd2bade
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/acc010e81f0b5de102362c90fb118a5b56e2c25e
@@ -0,0 +1,27 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: 7
+// CHECK:STDOUT: 3
+// CHECK:STDOUT: 0
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+class A { var n: i32; }
+
+impl A as ModWith(i32) where .Result = A {
+  fn Op[self: Self](rhs: i32) -> A { return {.n = self.n % rhs}; }
+}
+
+fn Main() -> i32 {
+  var a: A = {.n = 15};
+  a = a % 8;
+  Print("{0}", a.n);
+  a %= 4;
+  Print("{0}", a.n);
+  Print("{0}", (a % 3).n);
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/ae4a3a0f6a16334564bf7c43ce7ff480597c2cdb b/toolchain/semantics/fuzzer_corpus/ae4a3a0f6a16334564bf7c43ce7ff480597c2cdb
new file mode 100644
index 000000000000..35cc00b22348
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/ae4a3a0f6a16334564bf7c43ce7ff480597c2cdb
@@ -0,0 +1,38 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+interface ManyTypes {
+  let T0:! type;
+  let T1:! type;
+  let T2:! type;
+  let T3:! type;
+  let T4:! type;
+  let T5:! type;
+  let T6:! type;
+  let T7:! type;
+  let T8:! type;
+  let T9:! type;
+}
+
+fn F[
+  M:! ManyTypes where
+    .T0 = .T1 and
+    .T1 = .T2 and
+    .T2 = .T3 and
+    .T3 = .T4 and
+    .T4 = .T5 and
+    .T5 = .T6 and
+    .T6 = .T7 and
+    .T7 = .T8 and
+    .T8 = .T9 and
+    // CHECK:STDERR: COMPILATION ERROR: fail_rewrite_cycle.carbon:[[@LINE+1]]: rewrite of (M).(ManyTypes.T4) applies within its own resolved expansion of (M).(ManyTypes.T4)
+    .T9 = .T0]() {}
+
+fn Main() -> i32 {
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/ae4f2943ada6a47e2d5beb1a11629d617af1f8ce b/toolchain/semantics/fuzzer_corpus/ae4f2943ada6a47e2d5beb1a11629d617af1f8ce
new file mode 100644
index 000000000000..ab0424ade29e
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/ae4f2943ada6a47e2d5beb1a11629d617af1f8ce
@@ -0,0 +1,34 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: 0: Heap{}, 1: C{}
+// CHECK:STDOUT: Bind from c value expression
+// CHECK:STDOUT: Binding scope end
+// CHECK:STDOUT: c destroyed
+// CHECK:STDOUT: 0: Heap{}, 1: C{}, 2: !!C{}
+// CHECK:STDOUT: c destroyed
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+class C {
+  destructor[self: Self] {
+    Print("c destroyed");
+  }
+}
+
+fn CallWithReferenceExpressionBinding(var c: C) {
+  Print("Binding scope end");
+}
+
+fn Main() -> i32 {
+  let c_let: C = {};
+  heap.PrintAllocs();
+
+  Print("Bind from c value expression");
+  CallWithReferenceExpressionBinding(c_let);
+  heap.PrintAllocs();
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/af335f3fb6fda3927b5a8be215b9ce90c7e40539 b/toolchain/semantics/fuzzer_corpus/af335f3fb6fda3927b5a8be215b9ce90c7e40539
new file mode 100644
index 000000000000..a1977a058699
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/af335f3fb6fda3927b5a8be215b9ce90c7e40539
@@ -0,0 +1,16 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+fn id[T:! type](x: T) -> T {
+  return x;
+}
+
+fn Main() -> i32 {
+  return id(0);
+}
diff --git a/toolchain/semantics/fuzzer_corpus/b039b3b9343fd1c409690efa925a52c5e3cf9f3d b/toolchain/semantics/fuzzer_corpus/b039b3b9343fd1c409690efa925a52c5e3cf9f3d
new file mode 100644
index 000000000000..11bd1e8c3cf2
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/b039b3b9343fd1c409690efa925a52c5e3cf9f3d
@@ -0,0 +1,17 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  var t: auto = 5;
+  match (t) {
+    case x: i32 => {
+      return x - 5;
+    }
+  }
+}
diff --git a/toolchain/semantics/fuzzer_corpus/b091b7a85fd9dfb6e785a6ae16977ff1d2e20859 b/toolchain/semantics/fuzzer_corpus/b091b7a85fd9dfb6e785a6ae16977ff1d2e20859
new file mode 100644
index 000000000000..d31df7a8b1b9
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/b091b7a85fd9dfb6e785a6ae16977ff1d2e20859
@@ -0,0 +1,44 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: A(T) as B(i32)
+// CHECK:STDOUT: A(T) as B(U)
+// CHECK:STDOUT: A(i32) as B(T)
+// CHECK:STDOUT: A(i32) as B(T)
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+class A(T:! type) {}
+interface B(T:! type) {
+  fn F();
+}
+
+impl forall [T:! type] A(T) as B(i32) {
+  fn F() { Print("A(T) as B(i32)"); }
+}
+impl forall [T:! type] A(i32) as B(T) {
+  fn F() { Print("A(i32) as B(T)"); }
+}
+impl forall [T:! type, U:! type] A(T) as B(U) {
+  fn F() { Print("A(T) as B(U)"); }
+}
+
+fn F[T:! B(i32)](x: T) {
+  T.F();
+}
+fn G[T:! B(bool)](x: T) {
+  T.F();
+}
+
+fn Main() -> i32 {
+  let a: A(bool) = {};
+  let b: A(i32) = {};
+  F(a);
+  G(a);
+  F(b);
+  G(b);
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/b0f627cff7a9b69fbc6e7fee877e21eeb995fc94 b/toolchain/semantics/fuzzer_corpus/b0f627cff7a9b69fbc6e7fee877e21eeb995fc94
new file mode 100644
index 000000000000..60c3219664ec
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/b0f627cff7a9b69fbc6e7fee877e21eeb995fc94
@@ -0,0 +1,19 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+fn CompareStr(s: String) -> i32 {
+  // CHECK:STDERR: SYNTAX ERROR: fail_raw_more_hash_tags_on_right.carbon:[[@LINE+1]]: invalid character '\x23' in source file.
+  if (s == "str"#) {
+    return 0;
+  }
+  return 1;
+}
+
+fn Main() -> i32 {
+  return CompareStr("str");
+}
diff --git a/toolchain/semantics/fuzzer_corpus/b2674ac0752c471c50d74e2fa23f67e29cfdae08 b/toolchain/semantics/fuzzer_corpus/b2674ac0752c471c50d74e2fa23f67e29cfdae08
new file mode 100644
index 000000000000..fd4ac5b03d55
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/b2674ac0752c471c50d74e2fa23f67e29cfdae08
@@ -0,0 +1,17 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+fn AddInt(a: i32, b: i32) -> i32 {
+  // CHECK:STDERR: COMPILATION ERROR: fail_returned_var_type_mismatch.carbon:[[@LINE+1]]: type of returned var `bool` does not match return type `i32`
+  returned var ret: bool = true;
+  return var;
+}
+
+fn Main() -> i32 {
+  return AddInt(1, 2);
+}
diff --git a/toolchain/semantics/fuzzer_corpus/b2ffa84347526820d4fd74cc1e4b05245c8f3138 b/toolchain/semantics/fuzzer_corpus/b2ffa84347526820d4fd74cc1e4b05245c8f3138
new file mode 100644
index 000000000000..77ccee3f0b46
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/b2ffa84347526820d4fd74cc1e4b05245c8f3138
@@ -0,0 +1,16 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// TODO: This SHOULD fail but doesn't presently.
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+import Nonexistent;
+
+fn Main() -> i32 {
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/b32770014a39c3d995257c8a4c9c7850720bc3b6 b/toolchain/semantics/fuzzer_corpus/b32770014a39c3d995257c8a4c9c7850720bc3b6
new file mode 100644
index 000000000000..67f0dd9cd4b6
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/b32770014a39c3d995257c8a4c9c7850720bc3b6
@@ -0,0 +1,40 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: Carrot.G
+// CHECK:STDOUT: result: 5
+
+package ExplorerTest api;
+
+interface Apple(T:! type) {
+  fn F[self: Self]() -> T;
+}
+
+interface Banana {
+  require Self impls Apple(i32);
+  fn G[self: Self]();
+}
+
+class Carrot {
+  var n: i32;
+}
+
+impl Carrot as Apple(i32) {
+  fn F[self: Self]() -> i32 { return self.n; }
+}
+
+impl Carrot as Banana {
+  fn G[self: Self]() { Print("Carrot.G"); }
+}
+
+fn H[T:! Banana](x: T) -> i32 {
+  x.G();
+  return x.(Apple(i32).F)();
+}
+
+fn Main() -> i32 {
+  var c: Carrot = {.n = 5};
+  return H(c);
+}
diff --git a/toolchain/semantics/fuzzer_corpus/b36b4cfd1f0f6b5a74973d8b925e26f98d5c4fa6 b/toolchain/semantics/fuzzer_corpus/b36b4cfd1f0f6b5a74973d8b925e26f98d5c4fa6
new file mode 100644
index 000000000000..fc0eaf15368e
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/b36b4cfd1f0f6b5a74973d8b925e26f98d5c4fa6
@@ -0,0 +1,33 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 1133
+
+package ExplorerTest api;
+
+interface I(T:! type) {
+  fn F[self: Self](t: T, o: Self) -> Self;
+}
+
+class X(U:! type) {
+  extend impl as I(U) {
+    fn F[self: Self](u: U, o: Self) -> Self { return {.m = u, .n = self.n + o.n}; }
+  }
+  var m: U;
+  var n: i32;
+}
+
+fn Run[V:! type](x: V) -> (V, V, i32, i32) {
+  var v: X(V) = {.m = x, .n = 1};
+  var w: X(V) = {.m = x, .n = 2};
+  // OK, know that `X(V)` implements `I(V)` from the `impl` in the class.
+  var call: X(V) = v.(X(V).(I(V).F))(x, w);
+  return (call.(X(V).m), call.m, call.(X(V).n), call.n);
+}
+
+fn Main() -> i32 {
+  var (a: i32, b: i32, c: i32, d: i32) = Run(1);
+  return a * 1000 + b * 100 + c * 10 + d;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/b3d7c16243e6d943b2a4e180d9151cecd4c08e64 b/toolchain/semantics/fuzzer_corpus/b3d7c16243e6d943b2a4e180d9151cecd4c08e64
new file mode 100644
index 000000000000..c895f48699a5
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/b3d7c16243e6d943b2a4e180d9151cecd4c08e64
@@ -0,0 +1,18 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+interface FrobWith(T:! type) {}
+
+fn F[T:! FrobWith(.Self),
+     // CHECK:STDERR: COMPILATION ERROR: fail_dot_self_after_scope_2.carbon:[[@LINE+1]]: `.Self` used in type of non-type generic binding `U`
+     U:! .Self]() {
+}
+
+fn Main() -> i32 {
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/b444d666a312c8082f538078de9424a85fb83811 b/toolchain/semantics/fuzzer_corpus/b444d666a312c8082f538078de9424a85fb83811
new file mode 100644
index 000000000000..06c7208301c5
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/b444d666a312c8082f538078de9424a85fb83811
@@ -0,0 +1,28 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+interface Z {
+  fn Zero() -> Self;
+}
+
+class Point {
+  var x: i32;
+  var y: i32;
+  // `Self` not allowed after `extend impl`.
+  // CHECK:STDERR: SYNTAX ERROR: fail_extend_with_self.carbon:[[@LINE+1]]: syntax error, unexpected SELF, expecting AS
+  extend impl Self as Z {
+    fn Zero() -> Self {
+      return {.x = 0, .y = 0};
+    }
+  }
+}
+
+fn Main() -> i32 {
+  var a: Point = Point.Zero();
+  return p.x;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/b4a3ef5dc70af7bf091693b5db3e5e20f946d990 b/toolchain/semantics/fuzzer_corpus/b4a3ef5dc70af7bf091693b5db3e5e20f946d990
new file mode 100644
index 000000000000..fcb17edef702
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/b4a3ef5dc70af7bf091693b5db3e5e20f946d990
@@ -0,0 +1,21 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+class Point {
+  var x: i32;
+  var y: i32;
+}
+
+fn GetX(p: Point) -> i32 {
+  return p.x;
+}
+
+fn Main() -> i32 {
+  return GetX({.x = 1, .y = 2}) - 1;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/b4fbe7fa53f07fd1c43f29638c96356ccbdd4d81 b/toolchain/semantics/fuzzer_corpus/b4fbe7fa53f07fd1c43f29638c96356ccbdd4d81
new file mode 100644
index 000000000000..cb5a5e4fefb7
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/b4fbe7fa53f07fd1c43f29638c96356ccbdd4d81
@@ -0,0 +1,40 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+interface Vector {
+  fn Add[self: Self](b: Self) -> Self;
+  fn Scale[self: Self](v: i32) -> Self;
+}
+
+class Point {
+  var x: i32;
+  var y: i32;
+}
+
+impl Point as Vector {
+  fn Add[self: Point](b: Point) -> Point {
+    return {.x = self.x + b.x, .y = self.y + b.y};
+  }
+  fn Scale[self: Point](v: i32) -> Point {
+    return {.x = self.x * v, .y = self.y * v};
+  }
+}
+
+fn AddAndScaleGeneric[T:! Vector](a: T, b: T, s: i32) -> T {
+  var m: auto = a.Add;
+  var n: auto = m(b).Scale;
+  return n(s);
+}
+
+fn Main() -> i32 {
+  var a: Point = {.x = 1, .y = 4};
+  var b: Point = {.x = 2, .y = 3};
+  var p: Point = AddAndScaleGeneric(a, b, 5);
+  return p.x - 15;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/b5e44948070a88388a336b5873eb35c6f19534bf b/toolchain/semantics/fuzzer_corpus/b5e44948070a88388a336b5873eb35c6f19534bf
new file mode 100644
index 000000000000..239c7fb6bfd8
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/b5e44948070a88388a336b5873eb35c6f19534bf
@@ -0,0 +1,26 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 3
+
+package ExplorerTest api;
+
+interface HasAssoc {
+  let Assoc:! type;
+}
+class X {
+  impl as HasAssoc where .Assoc = i32 {}
+}
+
+fn H[T:! HasAssoc where .Assoc = i32, U:! type where .Self == i32](a: T, b: U) -> i32 {
+  var a: T.((HasAssoc where .Assoc = U).Assoc) = 3;
+  return a;
+}
+
+fn Main() -> i32 {
+  var x: X = {};
+  var y: i32 = 0;
+  return H(x, y);
+}
diff --git a/toolchain/semantics/fuzzer_corpus/b659fad4a34c3bff5cf5078a3d94215b8637ccae b/toolchain/semantics/fuzzer_corpus/b659fad4a34c3bff5cf5078a3d94215b8637ccae
new file mode 100644
index 000000000000..ce4386ad96ad
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/b659fad4a34c3bff5cf5078a3d94215b8637ccae
@@ -0,0 +1,14 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+// CHECK:STDERR: COMPILATION ERROR: fail_parameter_type_only.carbon:[[@LINE+1]]: An irrefutable pattern is required, but `i32` is refutable.
+fn f(x: i32, i32) {}
+
+fn Main() -> i32 {
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/b712c4641839c062c5f581a67665f38ab9532665 b/toolchain/semantics/fuzzer_corpus/b712c4641839c062c5f581a67665f38ab9532665
new file mode 100644
index 000000000000..173cafc5fb5d
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/b712c4641839c062c5f581a67665f38ab9532665
@@ -0,0 +1,14 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+// CHECK:STDERR: COMPILATION ERROR: fail_not_type.carbon:[[@LINE+1]]: type error in type expression: 'i32' is not implicitly convertible to 'type'
+fn F[a:! 42]();
+
+fn Main() -> i32 {
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/b7b4b3663513c4530e99086904fbb7108200bc77 b/toolchain/semantics/fuzzer_corpus/b7b4b3663513c4530e99086904fbb7108200bc77
new file mode 100644
index 000000000000..b5c4b067aab5
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/b7b4b3663513c4530e99086904fbb7108200bc77
@@ -0,0 +1,15 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+fn Bad[T:! type](x: {.a: i32, .b: T}) {}
+
+fn Main() -> i32 {
+  // CHECK:STDERR: COMPILATION ERROR: fail_implicit_conversion_extra_field.carbon:[[@LINE+1]]: mismatch in field names, source field `c` not in destination type `{.a: i32, .b: T}`
+  Bad({.b = 5, .a = 7, .c = 2});
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/b8c5b163cdd52c3dcbf7e22193574683199b623e b/toolchain/semantics/fuzzer_corpus/b8c5b163cdd52c3dcbf7e22193574683199b623e
new file mode 100644
index 000000000000..31cc4010a522
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/b8c5b163cdd52c3dcbf7e22193574683199b623e
@@ -0,0 +1,16 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+__mixin Mixin {
+  // CHECK:STDERR: COMPILATION ERROR: fail_mix_invalid.carbon:[[@LINE+1]]: Not a valid mixin: `()`
+  __mix ();
+}
+
+fn Main() -> i32 {
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/b8d30bb681704e28b89a62f19a1c5846ff7b2b9d b/toolchain/semantics/fuzzer_corpus/b8d30bb681704e28b89a62f19a1c5846ff7b2b9d
new file mode 100644
index 000000000000..41d565fab3a6
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/b8d30bb681704e28b89a62f19a1c5846ff7b2b9d
@@ -0,0 +1,15 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+interface Iface {
+  let T:! type;
+  // CHECK:STDERR: COMPILATION ERROR: fail_redefined.carbon:[[@LINE+1]]: Duplicate name `T` also found at fail_redefined.carbon:[[@LINE-1]]
+  let T:! type;
+}
+
+fn Main() -> i32 { return 0; }
diff --git a/toolchain/semantics/fuzzer_corpus/b949eac08c4054892d0142d5bda771e1cb4ffa05 b/toolchain/semantics/fuzzer_corpus/b949eac08c4054892d0142d5bda771e1cb4ffa05
new file mode 100644
index 000000000000..d5842b456e9f
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/b949eac08c4054892d0142d5bda771e1cb4ffa05
@@ -0,0 +1,41 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+interface Vector {
+  fn Add[self: Self](b: Self) -> Self;
+  fn Scale[self: Self](v: i32) -> Self;
+}
+
+class Point {
+  var x: i32;
+  var y: i32;
+}
+
+// Error: need to specify which type implementing `Vector` for.
+// CHECK:STDERR: COMPILATION ERROR: fail_external_impl_omit_self.carbon:[[@LINE+1]]: could not resolve 'Self'
+impl as Vector {
+  fn Add[self: Point](b: Point) -> Point {
+    return {.x = self.x + b.x, .y = self.y + b.y};
+  }
+  fn Scale[self: Point](v: i32) -> Point {
+    return {.x = self.x * v, .y = self.y * v};
+  }
+}
+
+fn AddAndScaleGeneric[T:! Vector](a: T, b: T, s: i32) -> T {
+  var m: auto = a.Add;
+  var n: auto = m(b).Scale;
+  return n(s);
+}
+
+fn Main() -> i32 {
+  var a: Point = {.x = 1, .y = 4};
+  var b: Point = {.x = 2, .y = 3};
+  var p: Point = AddAndScaleGeneric(a, b, 5);
+  return p.x - 15;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/b97f2101ca5e7b87bae66b45cd511a8f709496a9 b/toolchain/semantics/fuzzer_corpus/b97f2101ca5e7b87bae66b45cd511a8f709496a9
new file mode 100644
index 000000000000..5800f94a2e3b
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/b97f2101ca5e7b87bae66b45cd511a8f709496a9
@@ -0,0 +1,18 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+class Point {
+  var x: i32;
+  var y: i32;
+}
+
+fn Main() -> i32 {
+  var p: Point = {.x = 1, .y = 2};
+  return p.y - p.x - 1;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/ba1af5fb5ac955a0a4da3890243d68fd1ccddca0 b/toolchain/semantics/fuzzer_corpus/ba1af5fb5ac955a0a4da3890243d68fd1ccddca0
new file mode 100644
index 000000000000..b51c326a7da6
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/ba1af5fb5ac955a0a4da3890243d68fd1ccddca0
@@ -0,0 +1,26 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+class Point(T:! type) {
+  // CHECK:STDERR: COMPILATION ERROR: fail_two_arg_lists.carbon:[[@LINE+1]]: in call `Point(T)(T)`, expected callee to be a function, found `type`
+  fn Origin(zero: T) -> Point(T)(T) {
+    return {.x = zero, .y = zero};
+  }
+
+  fn GetX[self: Point(T)(T)]() -> T {
+    return self.x;
+  }
+
+  var x: T;
+  var y: T;
+}
+
+fn Main() -> i32 {
+  var p: Point(i32) = Point(i32).Origin(0);
+  return p.GetX();
+}
diff --git a/toolchain/semantics/fuzzer_corpus/bc00968d3030cf3aa5e2942dab6d5857a821c3c0 b/toolchain/semantics/fuzzer_corpus/bc00968d3030cf3aa5e2942dab6d5857a821c3c0
new file mode 100644
index 000000000000..c627a981be5c
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/bc00968d3030cf3aa5e2942dab6d5857a821c3c0
@@ -0,0 +1,17 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+// Demonstrate the aliasing behavior of pointers.
+
+fn Main() -> i32 {
+  var p: i32* = heap.New(5);
+  var q: i32* = p;
+  *q = 0;
+  return *p;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/bc1b6d2505d65d64d6ca362158e2c2ec3dd83577 b/toolchain/semantics/fuzzer_corpus/bc1b6d2505d65d64d6ca362158e2c2ec3dd83577
new file mode 100644
index 000000000000..07bf1c3ae6ce
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/bc1b6d2505d65d64d6ca362158e2c2ec3dd83577
@@ -0,0 +1,17 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+class A {}
+
+fn Main() -> i32 {
+  var a: A = {};
+  // CHECK:STDERR: COMPILATION ERROR: fail_no_mul.carbon:[[@LINE+2]]: type error in `*`:
+  // CHECK:STDERR: could not find implementation of interface MulWith(U = i32) for class A
+  a * 1;
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/bc3e368a7f2a1647772386571ac9efc52d0f6aff b/toolchain/semantics/fuzzer_corpus/bc3e368a7f2a1647772386571ac9efc52d0f6aff
new file mode 100644
index 000000000000..7302affef25c
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/bc3e368a7f2a1647772386571ac9efc52d0f6aff
@@ -0,0 +1,19 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 2
+
+package ExplorerTest api;
+
+fn A(b: bool) -> i32 {
+  match (b) {
+    case false => { return 1; }
+    case true => { return 2; }
+  }
+}
+
+fn Main() -> i32 {
+  return A(true);
+}
diff --git a/toolchain/semantics/fuzzer_corpus/bcb7fa4d022bd1099fce1eed15408ef42bd5346c b/toolchain/semantics/fuzzer_corpus/bcb7fa4d022bd1099fce1eed15408ef42bd5346c
new file mode 100644
index 000000000000..7eb4a0c1df7b
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/bcb7fa4d022bd1099fce1eed15408ef42bd5346c
@@ -0,0 +1,18 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  if (0 == 1) {
+    return 1;
+  } else {
+    return 0;
+  }
+
+  return 1;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/bcc107beab4b61b4c0b497a909470ae56ece14cd b/toolchain/semantics/fuzzer_corpus/bcc107beab4b61b4c0b497a909470ae56ece14cd
new file mode 100644
index 000000000000..d69f559aa0e3
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/bcc107beab4b61b4c0b497a909470ae56ece14cd
@@ -0,0 +1,26 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: d.a=1
+// CHECK:STDOUT: d.b=2
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+abstract class C {
+  var a: i32;
+}
+
+class D {
+  extend base: C;
+  var b: i32;
+}
+
+fn Main() -> i32 {
+  var d: D = { .base = {.a = 1}, .b = 2 };
+  Print("d.a={0}", d.a);
+  Print("d.b={0}", d.b);
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/bd4a8ee2367c6500f3a141093994d471f8c3f933 b/toolchain/semantics/fuzzer_corpus/bd4a8ee2367c6500f3a141093994d471f8c3f933
new file mode 100644
index 000000000000..374930240aa5
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/bd4a8ee2367c6500f3a141093994d471f8c3f933
@@ -0,0 +1,27 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+class Point {
+  fn Origin() -> Point {
+    return {.x = 0, .y = 0};
+  }
+
+  fn SetX[self: Point](x: i32) {
+    // CHECK:STDERR: COMPILATION ERROR: fail_method_args.carbon:[[@LINE+1]]: Only a reference expression can be assigned to, but got `x`
+    x = 10;
+  }
+
+  var x: i32;
+  var y: i32;
+}
+
+fn Main() -> i32 {
+  var p: Point = Point.Origin();
+  p.SetX(42);
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/bd5fb5758cb99b278455231a15b78acf6bd00857 b/toolchain/semantics/fuzzer_corpus/bd5fb5758cb99b278455231a15b78acf6bd00857
new file mode 100644
index 000000000000..724d0b98a5e6
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/bd5fb5758cb99b278455231a15b78acf6bd00857
@@ -0,0 +1,27 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: 3
+// CHECK:STDOUT: 7
+// CHECK:STDOUT: 15
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+class A { var n: i32; }
+
+impl A as BitOrWith(i32) where .Result = A {
+  fn Op[self: Self](rhs: i32) -> A { return {.n = self.n | rhs}; }
+}
+
+fn Main() -> i32 {
+  var a: A = {.n = 1};
+  a = a | 2;
+  Print("{0}", a.n);
+  a |= 5;
+  Print("{0}", a.n);
+  Print("{0}", (a | 12).n);
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/bd849c0012a2caf88ddd85bca8984481c146b973 b/toolchain/semantics/fuzzer_corpus/bd849c0012a2caf88ddd85bca8984481c146b973
new file mode 100644
index 000000000000..7677c9ee5aa4
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/bd849c0012a2caf88ddd85bca8984481c146b973
@@ -0,0 +1,10 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDERR: RUNTIME ERROR: <Main()>:0: attempt to call function `Main` that has not been defined
+
+package ExplorerTest api;
+
+fn Main() -> i32;
diff --git a/toolchain/semantics/fuzzer_corpus/be582a24883e7352f2038210d5ec0bab85ef2964 b/toolchain/semantics/fuzzer_corpus/be582a24883e7352f2038210d5ec0bab85ef2964
new file mode 100644
index 000000000000..98131eb84a20
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/be582a24883e7352f2038210d5ec0bab85ef2964
@@ -0,0 +1,20 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+class C {
+  fn F() {}
+  fn G[self: Self]() {}
+}
+
+fn ReturnF() -> auto { return C.F; }
+// CHECK:STDERR: COMPILATION ERROR: fail_return_method.carbon:[[@LINE+1]]: member name G can only be used in a member access or alias
+fn ReturnG() -> auto { return C.G; }
+
+fn Main() -> i32 {
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/bf0afbc4dfe5b6560b36212fd785221d72fe962b b/toolchain/semantics/fuzzer_corpus/bf0afbc4dfe5b6560b36212fd785221d72fe962b
new file mode 100644
index 000000000000..86940b5e3a33
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/bf0afbc4dfe5b6560b36212fd785221d72fe962b
@@ -0,0 +1,12 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  // CHECK:STDERR: SYNTAX ERROR: fail_invalid_integer.carbon:[[@LINE+1]]: Invalid integer literal: 11111111111111111111111111
+  return 11111111111111111111111111;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/bff54e1386ecdc1e2d26258dd98bb24e45c8993f b/toolchain/semantics/fuzzer_corpus/bff54e1386ecdc1e2d26258dd98bb24e45c8993f
new file mode 100644
index 000000000000..72eb2ca628ce
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/bff54e1386ecdc1e2d26258dd98bb24e45c8993f
@@ -0,0 +1,20 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  var x: i32 = 2;
+  while (true) {
+    if (x == 0) {
+      break;
+    } else {
+      x = x - 1;
+    }
+  }
+  return x;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/c06c7e4180fcc3902846677d5af1ce299ff04aaf b/toolchain/semantics/fuzzer_corpus/c06c7e4180fcc3902846677d5af1ce299ff04aaf
new file mode 100644
index 000000000000..d75d37421ed7
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/c06c7e4180fcc3902846677d5af1ce299ff04aaf
@@ -0,0 +1,37 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+class Cell(T:! type) {
+  fn Create(x: T) -> Cell(T) { return { .data = x }; }
+
+  fn Get[self: Self]() -> T {
+    return self.data;
+  }
+  fn Put[addr self: Self*](x: T) {
+    (*self).data = x;
+  }
+  fn CreateOther[self: Self, U:! type](x: U) -> Cell(U) {
+    return {.data = x};
+  }
+  var data: T;
+}
+
+class Integer {
+  var int: i32;
+}
+
+fn Main() -> i32 {
+  var i: Integer = {.int = 1};
+  var c: Cell(Integer) = Cell(Integer).Create(i);
+  i = {.int = 0};
+  c.Put(i);
+  var j: Integer = c.Get();
+  var d: Cell(Integer) = c.CreateOther(j);
+  return c.data.int + d.data.int;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/c1aaf1dd13a2d1ac0f10ccd627f5cf913b28e194 b/toolchain/semantics/fuzzer_corpus/c1aaf1dd13a2d1ac0f10ccd627f5cf913b28e194
new file mode 100644
index 000000000000..42b58272ee4f
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/c1aaf1dd13a2d1ac0f10ccd627f5cf913b28e194
@@ -0,0 +1,23 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: i32
+// CHECK:STDOUT: String
+// CHECK:STDOUT: result: 0
+
+package Testcase api;
+
+interface HasName {
+    let Name:! String;
+}
+
+impl i32 as HasName where .Name = "i32" {}
+impl String as HasName where .Name = "String" {}
+
+fn Main() -> i32 {
+    Print(i32.(HasName.Name));
+    Print(String.(HasName.Name));
+    return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/c27e3f5e51cd3b8574375da26d66b5dab5574d82 b/toolchain/semantics/fuzzer_corpus/c27e3f5e51cd3b8574375da26d66b5dab5574d82
new file mode 100644
index 000000000000..ded9d15a7355
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/c27e3f5e51cd3b8574375da26d66b5dab5574d82
@@ -0,0 +1,27 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: 6
+// CHECK:STDOUT: 0
+// CHECK:STDOUT: -1
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+class A { var n: i32; }
+
+impl A as BitXorWith(i32) where .Result = A {
+  fn Op[self: Self](rhs: i32) -> A { return {.n = self.n ^ rhs}; }
+}
+
+fn Main() -> i32 {
+  var a: A = {.n = 5};
+  a = a ^ 3;
+  Print("{0}", a.n);
+  a ^= 6;
+  Print("{0}", a.n);
+  Print("{0}", (a ^ -1).n);
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/c2ccd8521e3272b84287c5beed50b16ea6f83328 b/toolchain/semantics/fuzzer_corpus/c2ccd8521e3272b84287c5beed50b16ea6f83328
new file mode 100644
index 000000000000..e019b0b7663d
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/c2ccd8521e3272b84287c5beed50b16ea6f83328
@@ -0,0 +1,31 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: i32.F
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+interface Base {
+  fn F();
+}
+
+interface Extension {
+  extend Base;
+}
+
+fn F[T:! type where .Self impls Extension](x: T) {
+  x.(Extension.F)();
+}
+
+impl i32 as Extension {
+  fn F() { Print("i32.F"); }
+}
+
+fn Main() -> i32 {
+  var n: i32 = 0;
+  F(n);
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/c371479ed5d61900879832df3d14674b8bf586c4 b/toolchain/semantics/fuzzer_corpus/c371479ed5d61900879832df3d14674b8bf586c4
new file mode 100644
index 000000000000..6135a7d337b6
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/c371479ed5d61900879832df3d14674b8bf586c4
@@ -0,0 +1,16 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  // CHECK:STDERR: SYNTAX ERROR: fail_raw_block_more_hash_tags_on_left.carbon:[[@LINE+1]]: Unexpected end of file
+  var s: String = ##'''
+    error: there are more #s on the left than the right.
+  '''#;
+
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/c53cde1fb7e3ae52dbc9bae3da52905047adb174 b/toolchain/semantics/fuzzer_corpus/c53cde1fb7e3ae52dbc9bae3da52905047adb174
new file mode 100644
index 000000000000..4a827072dc2a
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/c53cde1fb7e3ae52dbc9bae3da52905047adb174
@@ -0,0 +1,16 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+fn F() {
+}
+
+fn Main() -> i32 {
+  F();
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/c62264ae938896c8ed1139a0fc215fb982e2fd69 b/toolchain/semantics/fuzzer_corpus/c62264ae938896c8ed1139a0fc215fb982e2fd69
new file mode 100644
index 000000000000..f80215b503c6
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/c62264ae938896c8ed1139a0fc215fb982e2fd69
@@ -0,0 +1,54 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: DESTRUCTOR A 1
+// CHECK:STDOUT: DESTRUCTOR A 2
+// CHECK:STDOUT: DESTRUCTOR A 3
+// CHECK:STDOUT: DESTRUCTOR A 4
+// CHECK:STDOUT: DESTRUCTOR A 5
+// CHECK:STDOUT: DESTRUCTOR A 6
+// CHECK:STDOUT: DESTRUCTOR A 7
+// CHECK:STDOUT: DESTRUCTOR A 8
+// CHECK:STDOUT: DESTRUCTOR A 6
+// CHECK:STDOUT: DESTRUCTOR A 7
+// CHECK:STDOUT: DESTRUCTOR A 8
+// CHECK:STDOUT: result: 1
+
+package ExplorerTest api;
+
+class A{
+    destructor[self: Self]{
+        Print("DESTRUCTOR A {0}",self.n);
+    }
+    var n: i32;
+}
+
+fn Main() -> i32 {
+  var i: i32 = 0;
+  while(true){
+      var a: A = {.n = 4};
+      var b: A = {.n = 3};
+      var c: A = {.n = 2};
+      if(true){
+        var a: A = {.n = 1};
+        break;
+      }
+  }
+
+  i = 0;
+  while(i < 2 ){
+    var a: A = {.n = 8};
+    var b: A = {.n = 7};
+    var c: A = {.n = 6};
+    if(i == 0){
+      var a: A = {.n = 5};
+      i = i+1;
+      continue;
+    }
+    i = i+1;
+  }
+
+  return 1;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/c64ac9d496e63e9f1b57dbbe870b16621d74ccd1 b/toolchain/semantics/fuzzer_corpus/c64ac9d496e63e9f1b57dbbe870b16621d74ccd1
new file mode 100644
index 000000000000..b2ebf22291a8
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/c64ac9d496e63e9f1b57dbbe870b16621d74ccd1
@@ -0,0 +1,20 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 20
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  var ar: [i32; 4] = (0, 1,2,3);
+   var count : i32 = 0;
+   for( x: i32 in ar){
+       count = count +1;
+        for( x: i32 in ar){
+            count = count +1;
+        }
+   }
+   return count;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/c7b5d3d001bf7f0224140706e7d747a9fbed9e82 b/toolchain/semantics/fuzzer_corpus/c7b5d3d001bf7f0224140706e7d747a9fbed9e82
new file mode 100644
index 000000000000..ba28dc474e54
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/c7b5d3d001bf7f0224140706e7d747a9fbed9e82
@@ -0,0 +1,25 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: Before: 1
+// CHECK:STDOUT: Interface: 2
+// CHECK:STDOUT: Op: 3
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+class C {
+  var n: i32;
+}
+
+fn Main() -> i32 {
+  var c: C = {.n = 1};
+  Print("Before: {0}", c.n);
+  c.(AssignWith({.n: i32}).Op)({.n = 2});
+  Print("Interface: {0}", c.n);
+  c = {.n = 3};
+  Print("Op: {0}", c.n);
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/c7fd0880feb951aeeef92e782305cf89df1edcaa b/toolchain/semantics/fuzzer_corpus/c7fd0880feb951aeeef92e782305cf89df1edcaa
new file mode 100644
index 000000000000..4300c8696644
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/c7fd0880feb951aeeef92e782305cf89df1edcaa
@@ -0,0 +1,14 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+constraint X {
+  // CHECK:STDERR: COMPILATION ERROR: fail_associated_function.carbon:[[@LINE+1]]: associated function not permitted in named constraint
+  fn F();
+}
+
+fn Main() -> i32 { return 0; }
diff --git a/toolchain/semantics/fuzzer_corpus/ca9f42d81e2b4a9a940d82785dcd497837d0f8c7 b/toolchain/semantics/fuzzer_corpus/ca9f42d81e2b4a9a940d82785dcd497837d0f8c7
new file mode 100644
index 000000000000..8461df90d6c4
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/ca9f42d81e2b4a9a940d82785dcd497837d0f8c7
@@ -0,0 +1,18 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: Hallo Welt
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+fn Main() -> i32{
+  var x: Optional(String) = Optional(String).Create( "Hallo Welt" );
+  if(x.HasValue()){
+    Print(x.Get());
+    return 0;
+  }
+  return -1;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/cb11afc40c6c53364bb4a113953adc9491e44eea b/toolchain/semantics/fuzzer_corpus/cb11afc40c6c53364bb4a113953adc9491e44eea
new file mode 100644
index 000000000000..b0fc424a8289
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/cb11afc40c6c53364bb4a113953adc9491e44eea
@@ -0,0 +1,16 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+class Point {
+  // CHECK:STDERR: COMPILATION ERROR: fail_qualified_method.carbon:[[@LINE+1]]: qualified declaration names are not permitted in this context
+  fn Point.F[self: Self]() {}
+}
+
+fn Main() -> i32 {
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/cbf37765b92964dcab9df8d0d85992170399dd57 b/toolchain/semantics/fuzzer_corpus/cbf37765b92964dcab9df8d0d85992170399dd57
new file mode 100644
index 000000000000..5277775d5258
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/cbf37765b92964dcab9df8d0d85992170399dd57
@@ -0,0 +1,15 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+fn F[T:! type & type](x: T) {}
+
+fn Main() -> i32 {
+  F(0);
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/cc232597fcd132b1012a688015feff43620a22ef b/toolchain/semantics/fuzzer_corpus/cc232597fcd132b1012a688015feff43620a22ef
new file mode 100644
index 000000000000..98075fbf195d
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/cc232597fcd132b1012a688015feff43620a22ef
@@ -0,0 +1,14 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest impl;
+
+fn Main() -> i32 {
+  // CHECK:STDERR: COMPILATION ERROR: fail_intrinsic_int_format.carbon:[[@LINE+3]]: type error in Print argument 0
+  // CHECK:STDERR: expected: String
+  // CHECK:STDERR: actual: i32
+  __intrinsic_print(0);
+}
diff --git a/toolchain/semantics/fuzzer_corpus/cc862b044a179be2a5cde3ff9e2070fea2a7e2cc b/toolchain/semantics/fuzzer_corpus/cc862b044a179be2a5cde3ff9e2070fea2a7e2cc
new file mode 100644
index 000000000000..de5fe95dc9a9
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/cc862b044a179be2a5cde3ff9e2070fea2a7e2cc
@@ -0,0 +1,15 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  var x: i32 = (1);
+  var t2: (i32, i32) = (5, 2);
+  t2[0] = 3;
+  return t2[0] - t2[1] - x;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/cce8949457022158df2d24b36f167db5f4acd9f7 b/toolchain/semantics/fuzzer_corpus/cce8949457022158df2d24b36f167db5f4acd9f7
new file mode 100644
index 000000000000..4609d9344b71
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/cce8949457022158df2d24b36f167db5f4acd9f7
@@ -0,0 +1,28 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 526
+
+package ExplorerTest api;
+
+interface A { fn F() -> i32; fn G() -> i32; }
+interface B { fn H() -> i32; }
+
+fn Get1[T:! A & B](n: T) -> i32 { return n.F() + n.H(); }
+fn Get2[T:! B & A](n: T) -> i32 { return n.G(); }
+fn Get3[T:! B & A & A & B & A](n: T) -> i32 { return n.G() + n.H(); }
+
+impl i32 as A {
+  fn F() -> i32 { return 1; }
+  fn G() -> i32 { return 2; }
+}
+impl i32 as B {
+  fn H() -> i32 { return 4; }
+}
+
+fn Main() -> i32 {
+  var z: i32 = 0;
+  return Get1(z) * 100 + Get2(z) * 10 + Get3(z);
+}
diff --git a/toolchain/semantics/fuzzer_corpus/cd45125269f01b6af10a764fdde04f35bab69ff8 b/toolchain/semantics/fuzzer_corpus/cd45125269f01b6af10a764fdde04f35bab69ff8
new file mode 100644
index 000000000000..336ede5d3f1b
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/cd45125269f01b6af10a764fdde04f35bab69ff8
@@ -0,0 +1,26 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+namespace N;
+namespace N.M;
+fn N.F() {}
+fn N.M.FM() {}
+
+alias A = N;
+alias AM = N.M;
+alias N.A = N.M;
+alias N.A2 = N;
+
+fn Main() -> i32 {
+  A.F();
+  AM.FM();
+  N.A.FM();
+  A.A2.A2.A2.A2.A2.A2.A2.F();
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/cda355e8d76ac84f9c04ce81d4b10c43ede462fa b/toolchain/semantics/fuzzer_corpus/cda355e8d76ac84f9c04ce81d4b10c43ede462fa
new file mode 100644
index 000000000000..854fc1b48e62
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/cda355e8d76ac84f9c04ce81d4b10c43ede462fa
@@ -0,0 +1,16 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+class C {
+  // CHECK:STDERR: COMPILATION ERROR: fail_member_of_self.carbon:[[@LINE+1]]: incomplete type `class C` used in type of variable
+  var m: Self;
+}
+
+fn Main() -> i32 {
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/ce4748f459444e0162224c3c7a549d2d233ae4a6 b/toolchain/semantics/fuzzer_corpus/ce4748f459444e0162224c3c7a549d2d233ae4a6
new file mode 100644
index 000000000000..eaf509fd912d
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/ce4748f459444e0162224c3c7a549d2d233ae4a6
@@ -0,0 +1,56 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 1
+
+package ExplorerTest api;
+
+interface ManyTypes {
+  let T0:! type;
+  let T1:! type;
+  let T2:! type;
+  let T3:! type;
+  let T4:! type;
+  let T5:! type;
+  let T6:! type;
+  let T7:! type;
+  let T8:! type;
+  let T9:! type;
+}
+
+fn F[
+  M:! ManyTypes where
+    .T0 = .T1 and
+    .T1 = .T2 and
+    .T2 = .T3 and
+    .T3 = .T4 and
+    .T4 = .T5 and
+    .T5 = .T6 and
+    .T6 = .T7 and
+    .T7 = .T8 and
+    .T8 = .T9 and
+    .T9 = i32](m: M) -> i32 {
+  var v: M.T0 = 1;
+  return v;
+}
+
+class C {
+  extend impl as ManyTypes where
+    .T0 = i32 and
+    .T1 = .T0 and
+    .T2 = .T1 and
+    .T3 = .T2 and
+    .T4 = .T3 and
+    .T5 = .T4 and
+    .T6 = .T5 and
+    .T7 = .T6 and
+    .T8 = .T7 and
+    .T9 = .T8 {}
+}
+
+fn Main() -> i32 {
+  var c: C = {};
+  return F(c);
+}
diff --git a/toolchain/semantics/fuzzer_corpus/cf4f9df21de1a0aead957f6d4733369928bb6422 b/toolchain/semantics/fuzzer_corpus/cf4f9df21de1a0aead957f6d4733369928bb6422
new file mode 100644
index 000000000000..e08969a7de47
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/cf4f9df21de1a0aead957f6d4733369928bb6422
@@ -0,0 +1,28 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+// TODO: Implement this with some kind of reflection?
+impl {.x: i32, .y: i32} as EqWith(Self) {
+  fn Equal[self: Self](other: Self) -> bool {
+    return self.x == other.x and self.y == other.y;
+  }
+  fn NotEqual[self: Self](other: Self) -> bool {
+    return self.x != other.x or self.y != other.y;
+  }
+}
+
+fn Main() -> i32 {
+  var t1: {.x: i32, .y: i32} = {.x = 5, .y = 2};
+  var t2: {.x: i32, .y: i32} = {.x = 5, .y = 4};
+  if (t1 == t2) {
+    return 1;
+  } else {
+    return 0;
+  }
+}
diff --git a/toolchain/semantics/fuzzer_corpus/d024760cfb19a4a0634f0bc0ed0668b9526fb1d4 b/toolchain/semantics/fuzzer_corpus/d024760cfb19a4a0634f0bc0ed0668b9526fb1d4
new file mode 100644
index 000000000000..1427147e60e0
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/d024760cfb19a4a0634f0bc0ed0668b9526fb1d4
@@ -0,0 +1,92 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: 1
+// CHECK:STDOUT: i32.Hash
+// CHECK:STDOUT: 0
+// CHECK:STDOUT: Potato.(Hashable.Hash)
+// CHECK:STDOUT: 1
+// CHECK:STDOUT: Potato.Hash
+// CHECK:STDOUT: 2
+// CHECK:STDOUT: Potato.Hash
+// CHECK:STDOUT: 2
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+interface Hashable {
+  fn Hash[self: Self]() -> i32;
+}
+
+class Potato {
+  impl as Hashable {
+    fn Hash[self: Self]() -> i32 {
+      Print("Potato.(Hashable.Hash)");
+      return 1;
+    }
+  }
+
+  fn Hash[self: Self]() -> i32 {
+    Print("Potato.Hash");
+    return 2;
+  }
+}
+
+interface Maker {
+  let Result:! Hashable;
+  fn Make() -> Result;
+}
+
+impl i32 as Hashable {
+  fn Hash[self: Self]() -> i32 {
+    Print("i32.Hash");
+    return self;
+  }
+}
+
+fn F[T:! Maker where .Result = i32](x: T) -> i32 {
+  // OK, can treat T.Make() as an i32.
+  return T.Make() + 1;
+}
+
+fn G[T:! Maker](x: T) -> i32 {
+  // OK, Potato.(Hashable.Hash), not Potato.Hash.
+  return T.Make().Hash();
+}
+
+fn H[T:! Maker where .Result = Potato](x: T) -> i32 {
+  // OK, Potato.Hash, not Potato.(Hashable.Hash).
+  return T.Make().Hash();
+}
+
+fn I[T:! Maker where .Result = Potato](x: T) -> i32 {
+  var p: Potato = {};
+  // OK, Potato.Hash, not Potato.(Hashable.Hash), even though we know Potato is
+  // Hashable here.
+  return p.Hash();
+}
+
+class IntFactory {
+  extend impl as Maker where .Result = i32 {
+    fn Make() -> i32 { return 0; }
+  }
+}
+
+class PotatoFactory {
+  extend impl as Maker where .Result = Potato {
+    fn Make() -> Potato { return {}; }
+  }
+}
+
+fn Main() -> i32 {
+  var f: IntFactory = {};
+  var g: PotatoFactory = {};
+  Print("{0}", F(f));
+  Print("{0}", G(f));
+  Print("{0}", G(g));
+  Print("{0}", H(g));
+  Print("{0}", I(g));
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/d0accc7215bdb8744f4809bb73c082ded2779896 b/toolchain/semantics/fuzzer_corpus/d0accc7215bdb8744f4809bb73c082ded2779896
new file mode 100644
index 000000000000..e8af1c206cbd
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/d0accc7215bdb8744f4809bb73c082ded2779896
@@ -0,0 +1,29 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 2
+
+package ExplorerTest api;
+
+interface HasAssoc {
+  let Assoc:! type;
+}
+class X {
+  impl as HasAssoc where .Assoc = i32 {}
+}
+
+alias WithoutRewrite = HasAssoc where .Assoc == i32;
+alias WithRewrite = HasAssoc where .Assoc = i32;
+
+fn G[T:! WithoutRewrite](x: T) -> i32 {
+  // TODO: We should reject this once `==` isn't applied automatically.
+  var a: T.(WithRewrite.Assoc) = 2;
+  return a;
+}
+
+fn Main() -> i32 {
+  var x: X = {};
+  return G(x);
+}
diff --git a/toolchain/semantics/fuzzer_corpus/d123ae0a5af4fc579954ea2a6791752f3cd0b6ec b/toolchain/semantics/fuzzer_corpus/d123ae0a5af4fc579954ea2a6791752f3cd0b6ec
new file mode 100644
index 000000000000..2e75c5a0b62e
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/d123ae0a5af4fc579954ea2a6791752f3cd0b6ec
@@ -0,0 +1,23 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+interface Similar(T:! type) {}
+
+impl forall [T:! type] T as Similar(T) {}
+impl forall [T:! type] i32 as Similar(T) {}
+
+fn CheckSimilar[T:! type, U:! Similar(T)](a: T, b: U) {}
+
+fn Main() -> i32 {
+  let n: i32 = 0;
+  CheckSimilar(true, false);
+  CheckSimilar(true, n);
+  // CHECK:STDERR: COMPILATION ERROR: fail_param_interface_in_impl.carbon:[[@LINE+1]]: could not find implementation of interface Similar(T = i32) for bool
+  CheckSimilar(n, false);
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/d156bf026dca3e2ad0c6542dcfbc5adb2b92d984 b/toolchain/semantics/fuzzer_corpus/d156bf026dca3e2ad0c6542dcfbc5adb2b92d984
new file mode 100644
index 000000000000..11c4399f4c1d
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/d156bf026dca3e2ad0c6542dcfbc5adb2b92d984
@@ -0,0 +1,14 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest impl;
+
+interface I {}
+
+// CHECK:STDERR: COMPILATION ERROR: fail_call_at_compile_time.carbon:[[@LINE+1]]: Print called before run time
+impl forall [T:! String] Print(T) as I {}
+
+fn Main() -> i32 { return 0; }
diff --git a/toolchain/semantics/fuzzer_corpus/d1d59cb9c1123806753ceededad1e68260f28c02 b/toolchain/semantics/fuzzer_corpus/d1d59cb9c1123806753ceededad1e68260f28c02
new file mode 100644
index 000000000000..75bb4eb067df
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/d1d59cb9c1123806753ceededad1e68260f28c02
@@ -0,0 +1,17 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 4
+
+package ExplorerTest api;
+
+fn F[T:! ImplicitAs(type)](x: T) -> type { return x; }
+
+fn Main() -> i32 {
+  var v: (i32, i32) as type = (1, 2);
+  var w: F((i32, i32)) = (3, 4);
+  v = w;
+  return v[1];
+}
diff --git a/toolchain/semantics/fuzzer_corpus/d2080d3e83e7cd6bcf8502acc028ff081acfba37 b/toolchain/semantics/fuzzer_corpus/d2080d3e83e7cd6bcf8502acc028ff081acfba37
new file mode 100644
index 000000000000..98153af8f997
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/d2080d3e83e7cd6bcf8502acc028ff081acfba37
@@ -0,0 +1,17 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+fn F() -> () {
+  return ();
+}
+
+fn Main() -> i32 {
+  F();
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/d2128bc393e5c6c0f97aa258700f37ade1d467ee b/toolchain/semantics/fuzzer_corpus/d2128bc393e5c6c0f97aa258700f37ade1d467ee
new file mode 100644
index 000000000000..b8e0b2e3895c
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/d2128bc393e5c6c0f97aa258700f37ade1d467ee
@@ -0,0 +1,20 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+fn Id(t: type) -> auto { return t; }
+
+// Test non-trivial type expression in parameter type.
+
+fn f(x: Id(i32)) -> i32 {
+  return x;
+}
+
+fn Main() -> i32 {
+  return f(0);
+}
diff --git a/toolchain/semantics/fuzzer_corpus/d24fb7aa6d76ab5a6e9095f88f1e6068791c2d93 b/toolchain/semantics/fuzzer_corpus/d24fb7aa6d76ab5a6e9095f88f1e6068791c2d93
new file mode 100644
index 000000000000..6f55ad5a0405
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/d24fb7aa6d76ab5a6e9095f88f1e6068791c2d93
@@ -0,0 +1,42 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: Initialize c from initializing expression (return <expr>)
+// CHECK:STDOUT: Entering call
+// CHECK:STDOUT: 0: Heap{}, 1: !Uninit<class C>
+// CHECK:STDOUT: Object created, returning
+// CHECK:STDOUT: 0: Heap{}, 1: !Uninit<class C>, 2: C{}
+// CHECK:STDOUT: c destroyed
+// CHECK:STDOUT: 0: Heap{}, 1: C{}, 2: !!C{}
+// CHECK:STDOUT: c destroyed
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+class C {
+  destructor[self: Self] {
+    Print("c destroyed");
+  }
+}
+
+fn CallWithReturnExpression() -> C {
+  Print("Entering call");
+  heap.PrintAllocs();
+  var c: C = {};
+  Print("Object created, returning");
+  heap.PrintAllocs();
+  return c;
+}
+
+fn FromInitializingExpression_ReturnExpr() {
+  Print("Initialize c from initializing expression (return <expr>)");
+  var c: C = CallWithReturnExpression();
+  heap.PrintAllocs();
+}
+
+fn Main() -> i32 {
+  FromInitializingExpression_ReturnExpr();
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/d44923d4ad9d5e88759b7e8b73ba96656144547d b/toolchain/semantics/fuzzer_corpus/d44923d4ad9d5e88759b7e8b73ba96656144547d
new file mode 100644
index 000000000000..d37f614b1de2
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/d44923d4ad9d5e88759b7e8b73ba96656144547d
@@ -0,0 +1,19 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 2
+
+package ExplorerTest api;
+
+var call_count: i32 = 0;
+fn ReturnTrue() -> bool {
+  call_count = call_count + 1;
+  return true;
+}
+
+fn Main() -> i32 {
+  var result: bool = ReturnTrue() and ReturnTrue();
+  return if result then call_count else -1;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/d5bf5d73d3d23dda8fcefdc6ee677656b43ebad8 b/toolchain/semantics/fuzzer_corpus/d5bf5d73d3d23dda8fcefdc6ee677656b43ebad8
new file mode 100644
index 000000000000..b32bc9fdb268
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/d5bf5d73d3d23dda8fcefdc6ee677656b43ebad8
@@ -0,0 +1,21 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+// Never actually called, so this only tests typechecking and semantic analysis.
+fn F(n: i32, p: i32*, q: i32***) -> i32* {
+  var a: i32 = n * *p;
+  var b: i32 = a*n;
+  *p = b*(*p);
+  **q = p;
+  return **q;
+}
+
+fn Main() -> i32 {
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/d5dd762e4ac174102440e69ee85eaf4c0d8cf532 b/toolchain/semantics/fuzzer_corpus/d5dd762e4ac174102440e69ee85eaf4c0d8cf532
new file mode 100644
index 000000000000..72884b53916f
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/d5dd762e4ac174102440e69ee85eaf4c0d8cf532
@@ -0,0 +1,18 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  var x: auto = 2;
+  while (x != 0) {
+    x = x - 1;
+    continue;
+    x = x + 1;
+  }
+  return x;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/d6c15493108686c94662f0b08ed99e626e16fab7 b/toolchain/semantics/fuzzer_corpus/d6c15493108686c94662f0b08ed99e626e16fab7
new file mode 100644
index 000000000000..10abd7a8c696
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/d6c15493108686c94662f0b08ed99e626e16fab7
@@ -0,0 +1,20 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  var s: String = #'''
+    A block string literal
+    \
+    '''#;
+  if (s == "A block string literal\n\\\n") {
+    return 0;
+  } else {
+    return 1;
+  }
+}
diff --git a/toolchain/semantics/fuzzer_corpus/d6e613d75099261a4c26abf0efbf03f48084e913 b/toolchain/semantics/fuzzer_corpus/d6e613d75099261a4c26abf0efbf03f48084e913
new file mode 100644
index 000000000000..6b3181091864
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/d6e613d75099261a4c26abf0efbf03f48084e913
@@ -0,0 +1,33 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: 1: 1
+// CHECK:STDOUT: 2: 2
+// CHECK:STDOUT: 3: 3
+// CHECK:STDOUT: 4: 4
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+class A {
+  var n: i32;
+  impl as ImplicitAs(i32) {
+    fn Convert[self: Self]() -> i32 { return self.n; }
+  }
+}
+impl i32 as ImplicitAs(A) {
+  fn Convert[self: Self]() -> A { return {.n = self}; }
+}
+
+fn Main() -> i32 {
+  var arr1: [i32; 2] = (1, 2 as A);
+  Print("1: {0}", arr1[0]);
+  Print("2: {0}", arr1[1]);
+
+  var arr2: [A; 2] = (3, 4 as A);
+  Print("3: {0}", arr2[0].n);
+  Print("4: {0}", arr2[1].n);
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/d6ebebabaf129b9b53a10b3287236c126c4dd4c4 b/toolchain/semantics/fuzzer_corpus/d6ebebabaf129b9b53a10b3287236c126c4dd4c4
new file mode 100644
index 000000000000..e579f0bf0f55
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/d6ebebabaf129b9b53a10b3287236c126c4dd4c4
@@ -0,0 +1,29 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+choice AB {
+  A(),
+  B()
+}
+
+fn F() -> AB { return AB.A(); }
+
+fn Main() -> i32 {
+  match ((F(), F(), F(), F(), F(), F(), F(), F())) {
+    case (AB.A(), AB.A(), AB.A(), AB.A(), AB.A(), AB.A(), AB.A(), AB.A()) => { return 0; }
+    case (AB.B(), AB.A(), AB.A(), AB.A(), AB.A(), AB.A(), AB.A(), AB.A()) => { return 1; }
+    case (_: AB,  AB.B(), AB.A(), AB.A(), AB.A(), AB.A(), AB.A(), AB.A()) => { return 2; }
+    case (_: AB,  _: AB,  AB.B(), AB.A(), AB.A(), AB.A(), AB.A(), AB.A()) => { return 3; }
+    case (_: AB,  _: AB,  _: AB,  AB.B(), AB.A(), AB.A(), AB.A(), AB.A()) => { return 4; }
+    case (_: AB,  _: AB,  _: AB,  _: AB,  AB.B(), AB.A(), AB.A(), AB.A()) => { return 5; }
+    case (_: AB,  _: AB,  _: AB,  _: AB,  _: AB,  AB.B(), AB.A(), AB.A()) => { return 6; }
+    case (_: AB,  _: AB,  _: AB,  _: AB,  _: AB,  _: AB,  AB.B(), AB.A()) => { return 7; }
+    case (_: AB,  _: AB,  _: AB,  _: AB,  _: AB,  _: AB,  _: AB,  AB.B()) => { return 8; }
+  }
+}
diff --git a/toolchain/semantics/fuzzer_corpus/d6fd5d90b6e7549eaf183f533f12c616678538ae b/toolchain/semantics/fuzzer_corpus/d6fd5d90b6e7549eaf183f533f12c616678538ae
new file mode 100644
index 000000000000..3159f48f65be
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/d6fd5d90b6e7549eaf183f533f12c616678538ae
@@ -0,0 +1,13 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+// CHECK:STDERR: COMPILATION ERROR: fail_impl_as.carbon:[[@LINE+1]]: expected a constraint in impl declaration, found i32
+impl i32 as i32 {}
+
+fn Main() -> i32 {
+}
diff --git a/toolchain/semantics/fuzzer_corpus/d7d015ff09dfb67f0799dfeeeb735565887e4b50 b/toolchain/semantics/fuzzer_corpus/d7d015ff09dfb67f0799dfeeeb735565887e4b50
new file mode 100644
index 000000000000..537a87509a15
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/d7d015ff09dfb67f0799dfeeeb735565887e4b50
@@ -0,0 +1,20 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  var s: String = '''
+    A block string literal
+    \'''
+    ''';
+  if (s == "A block string literal\n'''\n") {
+    return 0;
+  } else {
+    return 1;
+  }
+}
diff --git a/toolchain/semantics/fuzzer_corpus/d89723c25665ed5021dd28e45776c750d82b0185 b/toolchain/semantics/fuzzer_corpus/d89723c25665ed5021dd28e45776c750d82b0185
new file mode 100644
index 000000000000..3d61d9d1ff7f
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/d89723c25665ed5021dd28e45776c750d82b0185
@@ -0,0 +1,92 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: 1
+// CHECK:STDOUT: 2
+// CHECK:STDOUT: 3
+// CHECK:STDOUT: 4
+// CHECK:STDOUT: 1
+// CHECK:STDOUT: 2
+// CHECK:STDOUT: 3
+// CHECK:STDOUT: 4
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+class ListElement{
+  fn Create(value: i32)->ListElement{
+    return {
+      .element = Optional(i32).Create(value),
+      .next = Optional(ListElement*).CreateEmpty()
+    };
+  }
+
+  fn set[addr self: Self*] (value: Optional(ListElement*)){
+    (*self).next = value;
+  }
+
+  var element: Optional(i32);
+  var next: Optional(ListElement*);
+}
+
+class List{
+  fn Create() -> List{
+    return {.next = Optional(ListElement*).CreateEmpty() };
+  }
+  fn insert[addr self: Self*] (value: i32){
+    if( not (*self).next.HasValue() ){
+      (*self).next = Optional(ListElement*).Create( heap.New(ListElement.Create(value)) );
+      return;
+    }
+    var iter: Optional(ListElement*) = (*self).next;
+    var node: auto = (iter.Get());
+    while((*node).next.HasValue()){
+      iter = (*node).next;
+      node = (iter.Get());
+    }
+    var v : ListElement* = iter.Get();
+    var x: Optional(ListElement*) = Optional(ListElement*).Create( heap.New(ListElement.Create(value) ));
+    (*v).set(x);
+  }
+
+  fn print[self: Self] (){
+    var iter: Optional(ListElement*) = self.next;
+    while(iter.HasValue()){
+      var node: auto = *(iter.Get());
+      Print("{0}",node.element.Get());
+      var node_ptr: auto = iter.Get();
+      iter = node.next;
+    }
+  }
+
+  fn clean[addr self: Self*] (){
+    var head: auto = (*self).next;
+    while(head.HasValue()){
+      var tmp: auto = head;
+      head = (*head.Get()).next;
+      heap.Delete(tmp.Get());
+    }
+    (*self).next= Optional(ListElement*).CreateEmpty();
+  }
+
+  var next: Optional(ListElement*);
+}
+
+fn Main() -> i32{
+  var list: List = List.Create();
+  list.insert(1);
+  list.insert(2);
+  list.insert(3);
+  list.insert(4);
+  list.print();
+  list.clean();
+  list.print();
+  list.insert(1);
+  list.insert(2);
+  list.insert(3);
+  list.insert(4);
+  list.print();
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/d8e999fde93a63c561311ca9b1e68e6cc0a1d2f5 b/toolchain/semantics/fuzzer_corpus/d8e999fde93a63c561311ca9b1e68e6cc0a1d2f5
new file mode 100644
index 000000000000..358242d29f25
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/d8e999fde93a63c561311ca9b1e68e6cc0a1d2f5
@@ -0,0 +1,30 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+class Point {
+  fn Origin() -> Point {
+    return {.x = 0, .y = 0};
+  }
+
+  fn GetX[self: Point]() -> i32 {
+    return self.x;
+  }
+
+  fn GetXY[self: Point]() -> (i32, i32) {
+    return (self.GetX(), self.y);
+  }
+
+  var x: i32;
+  var y: i32;
+}
+
+fn Main() -> i32 {
+  var p: Point = Point.Origin();
+  return p.GetXY()[0];
+}
diff --git a/toolchain/semantics/fuzzer_corpus/d8fab3ec1a5e5cc74cf915da2a182a47dde177ff b/toolchain/semantics/fuzzer_corpus/d8fab3ec1a5e5cc74cf915da2a182a47dde177ff
new file mode 100644
index 000000000000..b59c05993cbe
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/d8fab3ec1a5e5cc74cf915da2a182a47dde177ff
@@ -0,0 +1,20 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  var s: String = '''filetype
+    A "block" ""string"" literal
+      with file type indicator.
+    ''';
+  if (s == "A \"block\" \"\"string\"\" literal\n  with file type indicator.\n") {
+    return 0;
+  } else {
+    return 1;
+  }
+}
diff --git a/toolchain/semantics/fuzzer_corpus/d982134d38f2ad7437e7faeba8a70c2d7c926b9a b/toolchain/semantics/fuzzer_corpus/d982134d38f2ad7437e7faeba8a70c2d7c926b9a
new file mode 100644
index 000000000000..0b8223a22359
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/d982134d38f2ad7437e7faeba8a70c2d7c926b9a
@@ -0,0 +1,30 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: 1
+// CHECK:STDOUT: 3
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+interface GetX {
+  fn DoIt[self: Self]() -> i32;
+}
+
+impl forall [template T:! type] T as GetX {
+  fn DoIt[self: Self]() -> i32 { return self.x; }
+}
+
+class C {
+  var x: i32;
+}
+
+fn Main() -> i32 {
+  var a: auto = {.x = 1, .y = 2};
+  var b: C = {.x = 3};
+  Print("{0}", a.(GetX.DoIt)());
+  Print("{0}", b.(GetX.DoIt)());
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/dacbcf23792118db3ab1ac01739fb1746f677991 b/toolchain/semantics/fuzzer_corpus/dacbcf23792118db3ab1ac01739fb1746f677991
new file mode 100644
index 000000000000..a596d0bfa48e
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/dacbcf23792118db3ab1ac01739fb1746f677991
@@ -0,0 +1,12 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 7
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  return (1 + 2) + 4;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/db1e5ec70d15bbfc7afd16f53ab14b24032e6ab0 b/toolchain/semantics/fuzzer_corpus/db1e5ec70d15bbfc7afd16f53ab14b24032e6ab0
new file mode 100644
index 000000000000..fbcd60d67e52
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/db1e5ec70d15bbfc7afd16f53ab14b24032e6ab0
@@ -0,0 +1,68 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: XYZ: 1
+// CHECK:STDOUT: XY: 1
+// CHECK:STDOUT: XZ: 1
+// CHECK:STDOUT: YZ: 2
+// CHECK:STDOUT: JustX: 1
+// CHECK:STDOUT: JustY: 2
+// CHECK:STDOUT: JustZ: 3
+// CHECK:STDOUT: None: 4
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+interface A {
+  fn Which() -> i32;
+}
+
+interface X {}
+interface Y {}
+interface Z {}
+
+__match_first {
+  impl forall [T:! X] T as A {
+    fn Which() -> i32 { return 1; }
+  }
+  impl forall [T:! Y] T as A {
+    fn Which() -> i32 { return 2; }
+  }
+  impl forall [T:! Z] T as A {
+    fn Which() -> i32 { return 3; }
+  }
+  impl forall [T:! type] T as A {
+    fn Which() -> i32 { return 4; }
+  }
+}
+
+class XYZ {}
+class XY {}
+class XZ {}
+class YZ {}
+class JustX {}
+class JustY {}
+class JustZ {}
+class None {}
+
+impl XYZ as X & Y & Z {}
+impl XY as X & Y {}
+impl XZ as X & Z {}
+impl YZ as Y & Z {}
+impl JustX as X {}
+impl JustY as Y {}
+impl JustZ as Z {}
+
+fn Main() -> i32 {
+  Print("XYZ: {0}", XYZ.(A.Which)());
+  Print("XY: {0}", XY.(A.Which)());
+  Print("XZ: {0}", XZ.(A.Which)());
+  Print("YZ: {0}", YZ.(A.Which)());
+  Print("JustX: {0}", JustX.(A.Which)());
+  Print("JustY: {0}", JustY.(A.Which)());
+  Print("JustZ: {0}", JustZ.(A.Which)());
+  Print("None: {0}", None.(A.Which)());
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/db794cf537ed613114f9612f9adc2218a8539120 b/toolchain/semantics/fuzzer_corpus/db794cf537ed613114f9612f9adc2218a8539120
new file mode 100644
index 000000000000..3f9b26c27ef2
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/db794cf537ed613114f9612f9adc2218a8539120
@@ -0,0 +1,28 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  if (^0 != -1) { return 11; }
+  if (^1 != -2) { return 12; }
+  if (^(-3) != 2) { return 13; }
+
+  if (3 & 6 != 2) { return 21; }
+  if (-1 & 4 != 4) { return 22; }
+  if (-1 & -2 != -2) { return 23; }
+
+  if (1 | 4 != 5) { return 31; }
+  if (5 | 3 != 7) { return 32; }
+  if (-2 | 1 != -1) { return 33; }
+
+  if (1 ^ 4 != 5) { return 41; }
+  if (5 ^ 3 != 6) { return 42; }
+  if (-2 ^ -3 != 3) { return 43; }
+
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/db8531a2205eba4d74aac481d01b5412148a8609 b/toolchain/semantics/fuzzer_corpus/db8531a2205eba4d74aac481d01b5412148a8609
new file mode 100644
index 000000000000..277fb11989fa
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/db8531a2205eba4d74aac481d01b5412148a8609
@@ -0,0 +1,43 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: Allocate B
+// CHECK:STDOUT: DESTRUCTOR B
+// CHECK:STDOUT: DESTRUCTOR A
+// CHECK:STDOUT: Delete B
+// CHECK:STDOUT: DESTRUCTOR B
+// CHECK:STDOUT: DESTRUCTOR A
+// CHECK:STDOUT: Return
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+
+base class A{
+    destructor[self: Self] {
+        Print("DESTRUCTOR A");
+    }
+}
+
+class B {
+  extend base: A;
+    fn Create() -> Self{
+        return {.base={}};
+    }
+    destructor[self: Self] {
+        Print("DESTRUCTOR B");
+    }
+}
+
+fn Main() -> i32 {
+  Print("Allocate B");
+  var pb: B* = heap.New(B.Create());
+
+  Print("Delete B");
+  heap.Delete(pb);
+
+  Print("Return");
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/dc7c445144f467eeb64983646e925ae07328bcba b/toolchain/semantics/fuzzer_corpus/dc7c445144f467eeb64983646e925ae07328bcba
new file mode 100644
index 000000000000..04240c552684
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/dc7c445144f467eeb64983646e925ae07328bcba
@@ -0,0 +1,58 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 12345
+
+package ExplorerTest api;
+
+class Class { var a: i32; }
+class GenericClass(T:! type) { var a: T; }
+interface Interface { fn Make() -> Self; }
+interface GenericInterface(T:! type) { fn Make() -> (Self, T); }
+
+alias ClassAlias = Class;
+alias GenericClassAlias = GenericClass;
+alias ClassSpecializationAlias = GenericClassAlias(i32);
+alias InterfaceAlias = Interface;
+alias GenericInterfaceAlias = GenericInterface;
+alias InterfaceSpecializationAlias = GenericInterfaceAlias(i32);
+
+impl ClassAlias as InterfaceAlias {
+  fn Make() -> Self { return {.a = 1}; }
+}
+impl ClassSpecializationAlias as InterfaceSpecializationAlias {
+  fn Make() -> (Self, i32) { return ({.a = 2}, 3); }
+}
+alias S = {.a: i32};
+impl GenericClassAlias(S) as GenericInterfaceAlias(S) {
+  fn Make() -> (Self, {.a: i32}) { return ({.a = {.a = 4}}, {.a = 5}); }
+}
+
+fn CheckImplementsInterface[T:! Interface](x: T) -> T {
+  return T.Make();
+}
+fn CheckImplementsGenericInterface_i32
+    [T:! GenericInterface(i32)](x: T) -> (T, i32) {
+  return T.Make();
+}
+fn CheckImplementsGenericInterface_struct
+    [T:! GenericInterface(S)](x: T) -> (T, S) {
+  return T.Make();
+}
+
+fn Main() -> i32 {
+  var a: Class = {.a = 0};
+  a = CheckImplementsInterface(a);
+
+  var b: GenericClass(i32) = {.a = 0};
+  var (b2: GenericClass(i32), n: i32) =
+    CheckImplementsGenericInterface_i32(b);
+
+  var c: GenericClass({.a: i32}) = {.a = {.a = 0}};
+  var (c2: GenericClass({.a: i32}), s: S) =
+    CheckImplementsGenericInterface_struct(c);
+
+  return 10000 * a.a + 1000 * b2.a + 100 * n + 10 * c2.a.a + s.a;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/dcf555e0afac952817e896d91358c612433ad2b2 b/toolchain/semantics/fuzzer_corpus/dcf555e0afac952817e896d91358c612433ad2b2
new file mode 100644
index 000000000000..303930528300
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/dcf555e0afac952817e896d91358c612433ad2b2
@@ -0,0 +1,21 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 1
+
+package ExplorerTest api;
+
+class A {
+  var n: i32;
+}
+impl i32 as ImplicitAs(A) {
+  fn Convert[self: Self]() -> A { return {.n = self }; }
+}
+
+fn Main() -> i32 {
+  var a: A = {.n = 0};
+  a = 1;
+  return a.n;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/de8fd526adf2973943a05700448469fece94f857 b/toolchain/semantics/fuzzer_corpus/de8fd526adf2973943a05700448469fece94f857
new file mode 100644
index 000000000000..d6cfd95df95f
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/de8fd526adf2973943a05700448469fece94f857
@@ -0,0 +1,22 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 122
+
+package ExplorerTest api;
+
+interface A { fn F() -> i32; }
+interface B { fn F() -> i32; }
+
+impl i32 as A { fn F() -> i32 { return 1; } }
+impl i32 as B { fn F() -> i32 { return 2; } }
+
+fn GetAB(T:! B where .Self impls A) -> i32 {
+  return 100 * T.(A.F)() + 10 * T.(B.F)() + T.F();
+}
+
+fn Main() -> i32 {
+  return GetAB(i32);
+}
diff --git a/toolchain/semantics/fuzzer_corpus/dea6e9dba0dfa54f07f7299afb5a8fff207fe36e b/toolchain/semantics/fuzzer_corpus/dea6e9dba0dfa54f07f7299afb5a8fff207fe36e
new file mode 100644
index 000000000000..5caa8505f93d
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/dea6e9dba0dfa54f07f7299afb5a8fff207fe36e
@@ -0,0 +1,14 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+class X(T:! type) {}
+
+// CHECK:STDERR: COMPILATION ERROR: fail_non_type_self.carbon:[[@LINE+1]]: `.Self` used in type of non-type generic binding `T`
+fn F[T:! X(.Self)](x: T) {}
+
+fn Main() -> i32 { return 0; }
diff --git a/toolchain/semantics/fuzzer_corpus/def696015dee4401e01d3f28ae43b4c142f8685f b/toolchain/semantics/fuzzer_corpus/def696015dee4401e01d3f28ae43b4c142f8685f
new file mode 100644
index 000000000000..1ee9af4849de
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/def696015dee4401e01d3f28ae43b4c142f8685f
@@ -0,0 +1,20 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+fn CompareStr(s: String) -> i32 {
+  // CHECK:STDERR: SYNTAX ERROR: fail_raw_more_hash_tags_on_left.carbon:[[@LINE+2]]: missing closing quote in single-line string: ##"str"#) {
+  // CHECK:STDERR:
+  if (s == ##"str"#) {
+    return 0;
+  }
+  return 1;
+}
+
+fn Main() -> i32 {
+  return CompareStr("str");
+}
diff --git a/toolchain/semantics/fuzzer_corpus/dfc5226bc4e3ae2646b9ebc457e2d8b5c0af703f b/toolchain/semantics/fuzzer_corpus/dfc5226bc4e3ae2646b9ebc457e2d8b5c0af703f
new file mode 100644
index 000000000000..53f9296f8b26
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/dfc5226bc4e3ae2646b9ebc457e2d8b5c0af703f
@@ -0,0 +1,25 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: DESTRUCTOR A 0
+// CHECK:STDOUT: DESTRUCTOR A 1
+// CHECK:STDOUT: DESTRUCTOR A 2
+// CHECK:STDOUT: result: 1
+
+package ExplorerTest api;
+
+
+class A{
+    destructor[self: Self]{
+        Print("DESTRUCTOR A {0}",self.n);
+    }
+    var n: i32;
+}
+
+fn Main() -> i32 {
+  var a1: A = {.n = 2};
+  var a: [A; 2] = ({.n = 1},{.n = 0});
+  return 1;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/e03ed52b86e8c3c447feddc1c1c9c1e8a9d11a68 b/toolchain/semantics/fuzzer_corpus/e03ed52b86e8c3c447feddc1c1c9c1e8a9d11a68
new file mode 100644
index 000000000000..314e772510c1
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/e03ed52b86e8c3c447feddc1c1c9c1e8a9d11a68
@@ -0,0 +1,13 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  // CHECK:STDERR: COMPILATION ERROR: fail_negative_size.carbon:[[@LINE+1]]: Array size cannot be negative
+  var x: [i32; -1] = ();
+  return x[0];
+}
diff --git a/toolchain/semantics/fuzzer_corpus/e0d6028299cf3768cc940ded9a62d55f552626cf b/toolchain/semantics/fuzzer_corpus/e0d6028299cf3768cc940ded9a62d55f552626cf
new file mode 100644
index 000000000000..c554618d42b3
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/e0d6028299cf3768cc940ded9a62d55f552626cf
@@ -0,0 +1,14 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+// CHECK:STDERR: COMPILATION ERROR: fail_unknown_namespace.carbon:[[@LINE+1]]: name 'N' has not been declared in this scope
+fn N.F() {}
+
+fn Main() -> i32 {
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/e1138048729d4c9b1b655debd816e6f8fa5db3c5 b/toolchain/semantics/fuzzer_corpus/e1138048729d4c9b1b655debd816e6f8fa5db3c5
new file mode 100644
index 000000000000..e9b031374b80
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/e1138048729d4c9b1b655debd816e6f8fa5db3c5
@@ -0,0 +1,19 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 42
+
+package ExplorerTest api;
+
+class A {
+  extend impl as ImplicitAs(i32) {
+    fn Convert[self: Self]() -> i32 { return 42; }
+  }
+}
+
+fn Main() -> i32 {
+  var a: A = {};
+  return a;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/e19b661a0932282f448caf7d3fedd3b8c48fa551 b/toolchain/semantics/fuzzer_corpus/e19b661a0932282f448caf7d3fedd3b8c48fa551
new file mode 100644
index 000000000000..657add87fbf8
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/e19b661a0932282f448caf7d3fedd3b8c48fa551
@@ -0,0 +1,22 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+class Point {
+  fn Origin() -> Point {
+    return {.x = 0, .y = 0};
+  }
+
+  var x: i32;
+  var y: i32;
+}
+
+fn Main() -> i32 {
+  var f: __Fn() -> Point = Point.Origin;
+  return f().x;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/e25ab871af04cab76fa6c546132504aa96f3faaf b/toolchain/semantics/fuzzer_corpus/e25ab871af04cab76fa6c546132504aa96f3faaf
new file mode 100644
index 000000000000..f2206a64074e
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/e25ab871af04cab76fa6c546132504aa96f3faaf
@@ -0,0 +1,17 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 3
+
+package Foo api;
+class X {
+  fn F[self: Self](o: Self) -> Self { return {.n = self.n + o.n}; }
+  var n: i32;
+}
+fn Main() -> i32 {
+  var v: X = {.n = 1};
+  var w: X = {.n = 2};
+  return v.(X.F)(w).(X.n);
+}
diff --git a/toolchain/semantics/fuzzer_corpus/e2898735f5262d6c50f82f32ce5064b75a295a65 b/toolchain/semantics/fuzzer_corpus/e2898735f5262d6c50f82f32ce5064b75a295a65
new file mode 100644
index 000000000000..49b0c71c1a35
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/e2898735f5262d6c50f82f32ce5064b75a295a65
@@ -0,0 +1,15 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  var x: [i32;] = (0, 1);
+  var index: i32 = 1;
+  x[index] = 0;
+  return x[0] + x[1];
+}
diff --git a/toolchain/semantics/fuzzer_corpus/e2fab09c2abe74d199bcb899a087b265b1c3be60 b/toolchain/semantics/fuzzer_corpus/e2fab09c2abe74d199bcb899a087b265b1c3be60
new file mode 100644
index 000000000000..746ebd38f314
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/e2fab09c2abe74d199bcb899a087b265b1c3be60
@@ -0,0 +1,22 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 6
+
+package ExplorerTest api;
+
+// The constraint here resolves to:
+//
+//   MulWith(T) where <ConstraintSelf>.(MulWith(T).Result) == <ConstraintSelf>
+//
+// Note in particular that this involves a member of `MulWith(T)`, so we need
+// `T` to have a symbolic identity when checking its own type.
+fn DoMul[T:! MulWith(.Self) where .Result == .Self](x: T, y: T) -> T {
+  return x * y;
+}
+
+fn Main() -> i32 {
+  return DoMul(2, 3);
+}
diff --git a/toolchain/semantics/fuzzer_corpus/e43ad190c7a05b408d5b8f37b249188ad17d604e b/toolchain/semantics/fuzzer_corpus/e43ad190c7a05b408d5b8f37b249188ad17d604e
new file mode 100644
index 000000000000..833b2252a3a2
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/e43ad190c7a05b408d5b8f37b249188ad17d604e
@@ -0,0 +1,13 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  // CHECK:STDERR: COMPILATION ERROR: fail_too_many_args.carbon:[[@LINE+1]]: Print takes 1 or 2 arguments, received 5
+  Print("too", "many", "args", "to", "print");
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/e4423a3ef9ca66952fa4b4d7f5cbbca5adfd0f9c b/toolchain/semantics/fuzzer_corpus/e4423a3ef9ca66952fa4b4d7f5cbbca5adfd0f9c
new file mode 100644
index 000000000000..898d8f5553a1
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/e4423a3ef9ca66952fa4b4d7f5cbbca5adfd0f9c
@@ -0,0 +1,20 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: Nice!
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  var i: i32 = Rand(0, 100);
+  var j: i32 = Rand(0, 100);
+  if (i == j) {
+    Print("HALLO WELT");
+  } else {
+    Print("Nice!");
+  }
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/e46d4e048f036d89c5cca5f3162868a8c5a6f117 b/toolchain/semantics/fuzzer_corpus/e46d4e048f036d89c5cca5f3162868a8c5a6f117
new file mode 100644
index 000000000000..2355caa81d4e
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/e46d4e048f036d89c5cca5f3162868a8c5a6f117
@@ -0,0 +1,18 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+
+fn Main() -> i32 {
+  var ar: [i32; 0] = () ;
+  var count : i32 = 0;
+  for( x: i32 in ar ){
+      count = 2;
+  }
+  return count;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/e55351de4fa2d74ad5b31c7043567f06eecfa80d b/toolchain/semantics/fuzzer_corpus/e55351de4fa2d74ad5b31c7043567f06eecfa80d
new file mode 100644
index 000000000000..7dbd3030ab02
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/e55351de4fa2d74ad5b31c7043567f06eecfa80d
@@ -0,0 +1,37 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+choice AB {
+  A(),
+  B()
+}
+
+fn F() -> AB { return AB.A(); }
+
+fn Main() -> i32 {
+  // This is T8 from http://moscova.inria.fr/~maranget/papers/warn/warn014.html
+  match ((F(), F(), F(), F(), F(), F(), F(), F())) {
+    case (AB.A(), AB.A(), AB.A(), AB.A(), AB.A(), AB.A(), AB.A(), AB.A()) => { return 0; }
+    case (AB.B(), AB.B(), AB.B(), AB.B(), AB.B(), AB.B(), AB.B(), AB.B()) => { return 1; }
+    case (_: AB,  AB.A(), AB.A(), AB.A(), AB.A(), AB.A(), AB.A(), AB.A()) => { return 2; }
+    case (_: AB,  AB.B(), AB.B(), AB.B(), AB.B(), AB.B(), AB.B(), AB.B()) => { return 3; }
+    case (_: AB,  _: AB,  AB.A(), AB.A(), AB.A(), AB.A(), AB.A(), AB.A()) => { return 4; }
+    case (_: AB,  _: AB,  AB.B(), AB.B(), AB.B(), AB.B(), AB.B(), AB.B()) => { return 5; }
+    case (_: AB,  _: AB,  _: AB,  AB.A(), AB.A(), AB.A(), AB.A(), AB.A()) => { return 6; }
+    case (_: AB,  _: AB,  _: AB,  AB.B(), AB.B(), AB.B(), AB.B(), AB.B()) => { return 7; }
+    case (_: AB,  _: AB,  _: AB,  _: AB,  AB.A(), AB.A(), AB.A(), AB.A()) => { return 8; }
+    case (_: AB,  _: AB,  _: AB,  _: AB,  AB.B(), AB.B(), AB.B(), AB.B()) => { return 9; }
+    case (_: AB,  _: AB,  _: AB,  _: AB,  _: AB,  AB.A(), AB.A(), AB.A()) => { return 10; }
+    case (_: AB,  _: AB,  _: AB,  _: AB,  _: AB,  AB.B(), AB.B(), AB.B()) => { return 11; }
+    case (_: AB,  _: AB,  _: AB,  _: AB,  _: AB,  _: AB,  AB.A(), AB.A()) => { return 12; }
+    case (_: AB,  _: AB,  _: AB,  _: AB,  _: AB,  _: AB,  AB.B(), AB.B()) => { return 13; }
+    case (_: AB,  _: AB,  _: AB,  _: AB,  _: AB,  _: AB,  _: AB,  AB.A()) => { return 14; }
+    case (_: AB,  _: AB,  _: AB,  _: AB,  _: AB,  _: AB,  _: AB,  AB.B()) => { return 15; }
+  }
+}
diff --git a/toolchain/semantics/fuzzer_corpus/e63c8f2e9bfe81106c2ee20701edc9503166b5a0 b/toolchain/semantics/fuzzer_corpus/e63c8f2e9bfe81106c2ee20701edc9503166b5a0
new file mode 100644
index 000000000000..0b23fb5b73b9
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/e63c8f2e9bfe81106c2ee20701edc9503166b5a0
@@ -0,0 +1,31 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+choice AB {
+  A(),
+  B()
+}
+
+fn F() -> AB { return AB.A(); }
+
+fn Main() -> i32 {
+  // Note, this match is exhaustive, but it exceeds our depth limit.
+  match ((F(), F(), F(), F(), F(), F(), F(), F(), F())) {
+    case (AB.A(), AB.A(), AB.A(), AB.A(), AB.A(), AB.A(), AB.A(), AB.A(), AB.A()) => { return 0; }
+    case (AB.B(), AB.A(), AB.A(), AB.A(), AB.A(), AB.A(), AB.A(), AB.A(), AB.A()) => { return 1; }
+    case (_: AB,  AB.B(), AB.A(), AB.A(), AB.A(), AB.A(), AB.A(), AB.A(), AB.A()) => { return 2; }
+    case (_: AB,  _: AB,  AB.B(), AB.A(), AB.A(), AB.A(), AB.A(), AB.A(), AB.A()) => { return 3; }
+    case (_: AB,  _: AB,  _: AB,  AB.B(), AB.A(), AB.A(), AB.A(), AB.A(), AB.A()) => { return 4; }
+    case (_: AB,  _: AB,  _: AB,  _: AB,  AB.B(), AB.A(), AB.A(), AB.A(), AB.A()) => { return 5; }
+    case (_: AB,  _: AB,  _: AB,  _: AB,  _: AB,  AB.B(), AB.A(), AB.A(), AB.A()) => { return 6; }
+    case (_: AB,  _: AB,  _: AB,  _: AB,  _: AB,  _: AB,  AB.B(), AB.A(), AB.A()) => { return 7; }
+    case (_: AB,  _: AB,  _: AB,  _: AB,  _: AB,  _: AB,  _: AB,  AB.B(), AB.A()) => { return 8; }
+    case (_: AB,  _: AB,  _: AB,  _: AB,  _: AB,  _: AB,  _: AB,  _: AB,  AB.B()) => { return 9; }
+  }
+// CHECK:STDERR: COMPILATION ERROR: fail_exhaustive_exponential_9x.carbon:[[@LINE+1]]: non-exhaustive match may allow control-flow to reach the end of a function that provides a `->` return type
+}
diff --git a/toolchain/semantics/fuzzer_corpus/e658fe116862210da87f0899577af9c2a39229c7 b/toolchain/semantics/fuzzer_corpus/e658fe116862210da87f0899577af9c2a39229c7
new file mode 100644
index 000000000000..de0de82df432
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/e658fe116862210da87f0899577af9c2a39229c7
@@ -0,0 +1,35 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 12
+
+package ExplorerTest api;
+
+interface Runnable {
+  fn Run[self: Self]() -> i32;
+}
+
+interface Walkable {
+  fn Walk[self: Self]() -> i32;
+}
+
+constraint Traversible {
+  extend Runnable;
+  extend Walkable;
+}
+
+impl i32 as Traversible {
+  fn Run[self: i32]() -> i32 {
+    return 10 * self;
+  }
+  fn Walk[self: i32]() -> i32 {
+    return self + 1;
+  }
+}
+
+fn Main() -> i32 {
+  var n: i32 = 1;
+  return n.(Runnable.Run)() + n.(Walkable.Walk)();
+}
diff --git a/toolchain/semantics/fuzzer_corpus/e65f9f71488ae494dab2a1769c8f7aad2b2d2c0e b/toolchain/semantics/fuzzer_corpus/e65f9f71488ae494dab2a1769c8f7aad2b2d2c0e
new file mode 100644
index 000000000000..9808c65b3498
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/e65f9f71488ae494dab2a1769c8f7aad2b2d2c0e
@@ -0,0 +1,19 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 1
+
+package ExplorerTest api;
+
+var call_count: i32 = 0;
+fn ReturnTrue() -> bool {
+  call_count = call_count + 1;
+  return true;
+}
+
+fn Main() -> i32 {
+  var result: bool = ReturnTrue() or ReturnTrue();
+  return if result then call_count else -1;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/e78a1c7691f0f1d0cfbb72f2769c496375dd04ba b/toolchain/semantics/fuzzer_corpus/e78a1c7691f0f1d0cfbb72f2769c496375dd04ba
new file mode 100644
index 000000000000..07d735cbeb78
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/e78a1c7691f0f1d0cfbb72f2769c496375dd04ba
@@ -0,0 +1,13 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  var v: bool;
+  // CHECK:STDERR: COMPILATION ERROR: fail_if_cond.carbon:[[@LINE+1]]: use of uninitialized variable v
+  return if v then 1 else 2;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/e7ef2c2d8afe215740b56deaf30a4b4bfdf8d155 b/toolchain/semantics/fuzzer_corpus/e7ef2c2d8afe215740b56deaf30a4b4bfdf8d155
new file mode 100644
index 000000000000..34ec55c503da
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/e7ef2c2d8afe215740b56deaf30a4b4bfdf8d155
@@ -0,0 +1,15 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: Hello world!
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  var s: auto = "Hello world!";
+  Print(s);
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/e8c9f04411d114789432f5b5ee69a579154b1efc b/toolchain/semantics/fuzzer_corpus/e8c9f04411d114789432f5b5ee69a579154b1efc
new file mode 100644
index 000000000000..6e6041fd390f
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/e8c9f04411d114789432f5b5ee69a579154b1efc
@@ -0,0 +1,26 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 5
+
+package ExplorerTest api;
+
+class Point(T:! type) {
+  var x: T;
+  var y: T;
+}
+
+fn GetX[T:! type](pt: Point(T)) -> T {
+  return pt.x;
+}
+fn GetY(T:! type, pt: Point(T)) -> T {
+  return pt.y;
+}
+
+fn Main() -> i32 {
+  var p: Point(i32) = {.x = 1, .y = 2};
+  // TODO: Should `GetX({.x = 1, .y = 2})` work? See #1251.
+  return GetX(p) + GetY(i32, {.x = 3, .y = 4});
+}
diff --git a/toolchain/semantics/fuzzer_corpus/e8f83f0475b7aa7415e190c94ce1a42a0bdae647 b/toolchain/semantics/fuzzer_corpus/e8f83f0475b7aa7415e190c94ce1a42a0bdae647
new file mode 100644
index 000000000000..d63f329937e9
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/e8f83f0475b7aa7415e190c94ce1a42a0bdae647
@@ -0,0 +1,23 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 3
+
+package ExplorerTest api;
+
+
+
+
+fn Main() -> i32 {
+  var ar: [i32; 4] = (0, 1,2,3);
+  var count : i32 = 0;
+  for( x: i32 in ar){
+      count = count +x;
+      if( x == 2){
+        break;
+      }
+  }
+  return count;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/e8f8d81bcb2d00b480af6a7e6b469642d79a301e b/toolchain/semantics/fuzzer_corpus/e8f8d81bcb2d00b480af6a7e6b469642d79a301e
new file mode 100644
index 000000000000..e45394e4e731
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/e8f8d81bcb2d00b480af6a7e6b469642d79a301e
@@ -0,0 +1,13 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  // CHECK:STDERR: COMPILATION ERROR: fail_assign_to_rval.carbon:[[@LINE+1]]: Only a reference expression can be assigned to, but got `1`
+  1 = 0;
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/e9cbf6617e536aeba214c934e3bdaf0c078353ff b/toolchain/semantics/fuzzer_corpus/e9cbf6617e536aeba214c934e3bdaf0c078353ff
new file mode 100644
index 000000000000..aa9166afdda0
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/e9cbf6617e536aeba214c934e3bdaf0c078353ff
@@ -0,0 +1,14 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: Print: {0}
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  Print("Print: {{0}");
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/ea54be10885ecba80b88fbd97086a791b0717a88 b/toolchain/semantics/fuzzer_corpus/ea54be10885ecba80b88fbd97086a791b0717a88
new file mode 100644
index 000000000000..cdd99d0b86ed
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/ea54be10885ecba80b88fbd97086a791b0717a88
@@ -0,0 +1,21 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 5
+
+package ExplorerTest api;
+
+interface HasTypeAndValue {
+  let T:! type;
+  let V:! T;
+}
+
+fn F(X:! HasTypeAndValue where .T = i32 and .V = 5) -> i32 { return X.V; }
+
+impl i32 as HasTypeAndValue where .T = i32 and .V = 5 {}
+
+fn Main() -> i32 {
+  return F(i32);
+}
diff --git a/toolchain/semantics/fuzzer_corpus/ea9a466902e7e5de89ab73b1fb426fc8b5a6d995 b/toolchain/semantics/fuzzer_corpus/ea9a466902e7e5de89ab73b1fb426fc8b5a6d995
new file mode 100644
index 000000000000..64482fc25daa
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/ea9a466902e7e5de89ab73b1fb426fc8b5a6d995
@@ -0,0 +1,14 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 1
+
+package ExplorerTest api;
+
+var x: i32;
+
+fn Main() -> i32 {
+  return 1;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/eb86ced910a15a563fdf6b97b35561ad7a62634a b/toolchain/semantics/fuzzer_corpus/eb86ced910a15a563fdf6b97b35561ad7a62634a
new file mode 100644
index 000000000000..fa0be137c45e
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/eb86ced910a15a563fdf6b97b35561ad7a62634a
@@ -0,0 +1,18 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 1
+
+package Foo api;
+interface A { fn F() -> i32; }
+class X {
+  extend impl as A {
+    fn F() -> i32 { return 1; }
+  }
+}
+fn Main() -> i32 {
+  var a: X = {};
+  return a.(A.F)();
+}
diff --git a/toolchain/semantics/fuzzer_corpus/ebde8bbea6e7af4fb072907cfc9be00d971239ee b/toolchain/semantics/fuzzer_corpus/ebde8bbea6e7af4fb072907cfc9be00d971239ee
new file mode 100644
index 000000000000..f1aab77d6144
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/ebde8bbea6e7af4fb072907cfc9be00d971239ee
@@ -0,0 +1,13 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDERR: RUNTIME ERROR: {{.*}}/explorer/data/prelude.carbon:{{.*}}: "Attempted to unwrap empty Optional"
+
+package ExplorerTest api;
+
+fn Main() -> i32{
+  var x: Optional(i32) = Optional(i32).CreateEmpty();
+  return x.Get();
+}
diff --git a/toolchain/semantics/fuzzer_corpus/ed4b817bb59e605b98255e448092e811f6e82a1b b/toolchain/semantics/fuzzer_corpus/ed4b817bb59e605b98255e448092e811f6e82a1b
new file mode 100644
index 000000000000..3cf4be518a44
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/ed4b817bb59e605b98255e448092e811f6e82a1b
@@ -0,0 +1,39 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+interface Vector {
+  fn Add[self: Self](b: Self) -> Self;
+  fn Scale[self: Self](v: i32) -> Self;
+}
+
+class Point {
+  var x: i32;
+  var y: i32;
+  extend impl as Vector {
+    fn Add[self: Point](b: Point) -> Point {
+      return {.x = self.x + b.x, .y = self.y + b.y};
+    }
+    fn Scale[self: Point](v: i32) -> Point {
+      return {.x = self.x * v, .y = self.y * v};
+    }
+  }
+}
+
+fn AddAndScaleGeneric[T:! Vector](a: T, b: T, s: i32) -> T {
+  var m: __Fn(T)->T = a.Add;
+  var n: __Fn(i32)->T = m(b).Scale;
+  return n(s);
+}
+
+fn Main() -> i32 {
+  var a: Point = {.x = 1, .y = 1};
+  var b: Point = {.x = 2, .y = 3};
+  var p: Point = AddAndScaleGeneric(a, b, 5);
+  return p.x - 15;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/ef2e0af90b23b181ff4232ff151921baabbd6279 b/toolchain/semantics/fuzzer_corpus/ef2e0af90b23b181ff4232ff151921baabbd6279
new file mode 100644
index 000000000000..abff72fe64fb
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/ef2e0af90b23b181ff4232ff151921baabbd6279
@@ -0,0 +1,19 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: test
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+fn F() { Print("test"); }
+
+fn Main() -> i32 {
+  var p: auto = heap.New(F);
+  var y: auto = *p;
+  y();
+  heap.Delete(p);
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/ef85503e869dddcd31e3fda607c157093dd58aaa b/toolchain/semantics/fuzzer_corpus/ef85503e869dddcd31e3fda607c157093dd58aaa
new file mode 100644
index 000000000000..5b03936e776a
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/ef85503e869dddcd31e3fda607c157093dd58aaa
@@ -0,0 +1,16 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+// CHECK:STDERR: COMPILATION ERROR: fail_fn_use_in_return_type.carbon:[[@LINE+1]]: 'F' is not usable until after it has been completely declared
+fn F() -> F() {
+  return type;
+}
+
+fn Main() -> i32 {
+  return x;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/efca78c56911295c843344e70430e1f2a76ac3dd b/toolchain/semantics/fuzzer_corpus/efca78c56911295c843344e70430e1f2a76ac3dd
new file mode 100644
index 000000000000..fe1792b39c8a
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/efca78c56911295c843344e70430e1f2a76ac3dd
@@ -0,0 +1,33 @@
+
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+class B {
+  var x: i32;
+
+  fn GetSetX[addr self: Self*](x: i32) -> i32 {
+    var oldX: auto = (*self).x;
+    (*self).x = x;
+    return oldX;
+  }
+}
+
+class A {
+  var b: B;
+}
+
+fn Main() -> i32 {
+  var b: B = {.x = 0};
+  var a: A = {.b = b};
+  var x: auto = a.b.GetSetX(42);
+  if (a.b.x == 42) {
+    return x;
+  }
+  return 1;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/f2a23da83d1decfbd0d6b632d4e3a7c0fe83229a b/toolchain/semantics/fuzzer_corpus/f2a23da83d1decfbd0d6b632d4e3a7c0fe83229a
new file mode 100644
index 000000000000..64456c8e4eba
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/f2a23da83d1decfbd0d6b632d4e3a7c0fe83229a
@@ -0,0 +1,14 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  var t1: {.x: i32,} = {.x = 5,};
+  var t2: {.x: i32, .y: i32} = {.x = 2, .y = 3,};
+  return t1.x - t2.x - t2.y;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/f30e3a9ba4c393a1638833cb39b1af2fcf2c8f09 b/toolchain/semantics/fuzzer_corpus/f30e3a9ba4c393a1638833cb39b1af2fcf2c8f09
new file mode 100644
index 000000000000..05acaaa57284
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/f30e3a9ba4c393a1638833cb39b1af2fcf2c8f09
@@ -0,0 +1,20 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: -6
+
+package ExplorerTest api;
+
+class A { var n: i32; }
+
+impl A as BitComplement where .Result = A {
+  fn Op[self: Self]() -> A { return {.n = ^self.n}; }
+}
+
+fn Main() -> i32 {
+  var a: A = {.n = 5};
+  a = ^a;
+  return a.n;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/f34cf0e7e074d139df2a5550a9cb7bb904947386 b/toolchain/semantics/fuzzer_corpus/f34cf0e7e074d139df2a5550a9cb7bb904947386
new file mode 100644
index 000000000000..1cf573bceef0
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/f34cf0e7e074d139df2a5550a9cb7bb904947386
@@ -0,0 +1,18 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  var t: auto = (1, 2, 3, 4);
+  match (t) {
+    case (_: i32, _: auto, x: i32, y: auto) => {
+      return y - x - 1;
+    }
+  }
+  return 1;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/f4644987ac7761e6269cc798952123a412d60579 b/toolchain/semantics/fuzzer_corpus/f4644987ac7761e6269cc798952123a412d60579
new file mode 100644
index 000000000000..7c7e008db98e
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/f4644987ac7761e6269cc798952123a412d60579
@@ -0,0 +1,11 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 2
+
+package Foo api;
+fn Main() -> i32 {
+  return {.m = 1, .n = 2}.({.n: i32, .m: i32}.n);
+}
diff --git a/toolchain/semantics/fuzzer_corpus/f489479b6711f206c1674ab760a65ae1f611d23c b/toolchain/semantics/fuzzer_corpus/f489479b6711f206c1674ab760a65ae1f611d23c
new file mode 100644
index 000000000000..87364b5038b7
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/f489479b6711f206c1674ab760a65ae1f611d23c
@@ -0,0 +1,25 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: 1
+// CHECK:STDOUT: 1
+// CHECK:STDOUT: 1
+// CHECK:STDOUT: 1
+// CHECK:STDOUT: result: 0
+
+package Foo api;
+class X {
+  fn F[self: Self]() -> i32 { return self.n; }
+  var n: i32;
+}
+fn Main() -> i32 {
+  var v: X = {.n = 1};
+  let p: X* = &v;
+  Print("{0}", p->n);
+  Print("{0}", p->(X.n));
+  Print("{0}", p->F());
+  Print("{0}", p->(X.F)());
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/f50ed08142a8c7abf9eb8a0fe9a1560172460772 b/toolchain/semantics/fuzzer_corpus/f50ed08142a8c7abf9eb8a0fe9a1560172460772
new file mode 100644
index 000000000000..b6ed781e8e92
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/f50ed08142a8c7abf9eb8a0fe9a1560172460772
@@ -0,0 +1,41 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+__mixin Operations {
+  fn F[self: Self](x: Self) -> Self{
+     return x;
+  }
+}
+
+class Point {
+  fn Origin() -> Point {
+    return {.x = 0, .y = 0};
+  }
+
+  var x: i32;
+  var y: i32;
+  __mix Operations;
+}
+
+class Complex {
+  fn Zero() -> Complex {
+    return {.r = 0, .i = 0};
+  }
+
+  var r: i32;
+  var i: i32;
+}
+
+fn Main() -> i32 {
+  var p: Point = Point.Origin();
+  var c: Complex = {.r = 42, .i = 1};
+  // CHECK:STDERR: COMPILATION ERROR: fail_self_substitution.carbon:[[@LINE+1]]: mismatch in non-deduced types, `class Complex` is not implicitly convertible to `class Point`
+  var p1: Point = p.F(c);
+
+  return p1.x - 42;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/f684767b7018726978f04cec28fc3505e830c280 b/toolchain/semantics/fuzzer_corpus/f684767b7018726978f04cec28fc3505e830c280
new file mode 100644
index 000000000000..2c0cd7a99a07
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/f684767b7018726978f04cec28fc3505e830c280
@@ -0,0 +1,23 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 4213
+
+package ExplorerTest api;
+
+interface IntLike {
+  fn Convert[self: Self]() -> i32;
+}
+impl i32 as IntLike {
+  fn Convert[self: i32]() -> i32 { return self; }
+}
+
+fn add[T:! IntLike](x: {.a: T, .b: ({.m: i32, .n: T}, i32)}) -> i32 {
+  return 1000 * x.a.Convert() + 100 * x.b[0].m + 10 * x.b[0].n.Convert() + x.b[1];
+}
+
+fn Main() -> i32 {
+  return add({.b = ({.n = 1, .m = 2}, 3), .a = 4});
+}
diff --git a/toolchain/semantics/fuzzer_corpus/f690876af2536fe2aa69e30d6b0ed44df3ab37cf b/toolchain/semantics/fuzzer_corpus/f690876af2536fe2aa69e30d6b0ed44df3ab37cf
new file mode 100644
index 000000000000..d8a1fb36043a
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/f690876af2536fe2aa69e30d6b0ed44df3ab37cf
@@ -0,0 +1,19 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+fn CompareStr(s: String) -> i32 {
+  if (s == #"str"#) {
+    return 0;
+  }
+  return 1;
+}
+
+fn Main() -> i32 {
+  return CompareStr("str");
+}
diff --git a/toolchain/semantics/fuzzer_corpus/f7393ed8d9481808807434d4e757e0f8b11199f2 b/toolchain/semantics/fuzzer_corpus/f7393ed8d9481808807434d4e757e0f8b11199f2
new file mode 100644
index 000000000000..2e72f9c8c923
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/f7393ed8d9481808807434d4e757e0f8b11199f2
@@ -0,0 +1,25 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: Destructor A 3
+// CHECK:STDOUT: Destructor A 1
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+class A {
+  var i: i32;
+  destructor[self: Self] {
+    Print("Destructor A {0}", self.i);
+  }
+}
+
+fn Main() -> i32 {
+  var a0: A;
+  var a1: A = {.i = 1};
+  var a2: A;
+  var a3: A = {.i = 3};
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/f76a0f5a984ac0ce2b83dfd9b9a0f98a23c10db8 b/toolchain/semantics/fuzzer_corpus/f76a0f5a984ac0ce2b83dfd9b9a0f98a23c10db8
new file mode 100644
index 000000000000..865454c96d55
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/f76a0f5a984ac0ce2b83dfd9b9a0f98a23c10db8
@@ -0,0 +1,39 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+class Shape {
+  var x: i32;
+}
+
+class Point {
+
+  fn Origin() -> Point {
+    return {.x = 0, .y = 0};
+  }
+
+  fn GetSetX[addr self: Shape*](x: i32) -> i32 {
+    var old: auto = (*self).x;
+    (*self).x = x;
+    return old;
+  }
+
+  var x: i32;
+  var y: i32;
+}
+
+fn Main() -> i32 {
+  var p: Point = Point.Origin();
+  // CHECK:STDERR: COMPILATION ERROR: fail_method_self_type.carbon:[[@LINE+3]]: type error in method access, receiver type
+  // CHECK:STDERR: expected: class Shape
+  // CHECK:STDERR: actual: class Point
+  var x: auto = p.GetSetX(42);
+  if (p.x == 42) {
+    return x;
+  }
+  return 1;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/f7b635ace4157cf9aa35bf097ed316f49a1eeb4d b/toolchain/semantics/fuzzer_corpus/f7b635ace4157cf9aa35bf097ed316f49a1eeb4d
new file mode 100644
index 000000000000..adee17e917ba
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/f7b635ace4157cf9aa35bf097ed316f49a1eeb4d
@@ -0,0 +1,13 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDERR: RUNTIME ERROR: {{.*}}/explorer/data/prelude.carbon:{{.*}}: "HALLO WELT"
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  Assert(false, "HALLO WELT");
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/f7e0b4168e589c4c297e0247cc3d5f18c7251880 b/toolchain/semantics/fuzzer_corpus/f7e0b4168e589c4c297e0247cc3d5f18c7251880
new file mode 100644
index 000000000000..185cfa79e376
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/f7e0b4168e589c4c297e0247cc3d5f18c7251880
@@ -0,0 +1,14 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  var p: {.x: i32, .y: i32};
+  // CHECK:STDERR: COMPILATION ERROR: fail_struct_member_access.carbon:[[@LINE+1]]: use of uninitialized variable p
+  p.x = p.y;
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/f842eee360ff15762e838268ea620397372e278f b/toolchain/semantics/fuzzer_corpus/f842eee360ff15762e838268ea620397372e278f
new file mode 100644
index 000000000000..46cb82ab990a
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/f842eee360ff15762e838268ea620397372e278f
@@ -0,0 +1,31 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: 0: Heap{}, 1: C{}
+// CHECK:STDOUT: Initialize c from reference expression
+// CHECK:STDOUT: 0: Heap{}, 1: C{}
+// CHECK:STDOUT: c destroyed
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+class C {
+  destructor[self: Self] {
+    Print("c destroyed");
+  }
+}
+
+fn FromReferenceExpression() {
+  var c_var: C = {};
+  heap.PrintAllocs();
+  Print("Initialize c from reference expression");
+  let c: C = c_var;
+  heap.PrintAllocs();
+}
+
+fn Main() -> i32 {
+  FromReferenceExpression();
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/f86b41031c5d4d3bdac24f679b6057470f3e47c7 b/toolchain/semantics/fuzzer_corpus/f86b41031c5d4d3bdac24f679b6057470f3e47c7
new file mode 100644
index 000000000000..2dabfcf823a6
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/f86b41031c5d4d3bdac24f679b6057470f3e47c7
@@ -0,0 +1,20 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+namespace N;
+fn N.F() {}
+
+alias A = N;
+alias B = A;
+alias C = B;
+
+fn Main() -> i32 {
+  C.F();
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/faf03b2cec7b27856ad2faf2221466957630a6a5 b/toolchain/semantics/fuzzer_corpus/faf03b2cec7b27856ad2faf2221466957630a6a5
new file mode 100644
index 000000000000..e514f33b8761
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/faf03b2cec7b27856ad2faf2221466957630a6a5
@@ -0,0 +1,13 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  // CHECK:STDERR: SYNTAX ERROR: fail_hex_truncated.carbon:[[@LINE+1]]: Invalid escaping in string: "str\x"
+  Print("str\x");
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/fb9a1ebda410782881e93d1375d0199654fc3671 b/toolchain/semantics/fuzzer_corpus/fb9a1ebda410782881e93d1375d0199654fc3671
new file mode 100644
index 000000000000..b2cd39e6c5e1
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/fb9a1ebda410782881e93d1375d0199654fc3671
@@ -0,0 +1,55 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: 1
+// CHECK:STDOUT: 2
+// CHECK:STDOUT: 3
+// CHECK:STDOUT: 4
+// CHECK:STDOUT: 4
+// CHECK:STDOUT: 6
+// CHECK:STDOUT: 5
+// CHECK:STDOUT: 6
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+class A(T:! type, U:! type) {}
+interface B(T:! type, U:! type) { fn F(); }
+
+impl forall [T:! type] A(T, i32) as B(i32, i32) {
+  fn F() { Print("1"); }
+}
+impl forall [T:! type] A(i32, T) as B(i32, i32) {
+  fn F() { Print("2"); }
+}
+// Intentionally out of order so that explorer can't get the right answer by
+// chance, by just picking the first or last matching impl.
+impl forall [T:! type] A(i32, i32) as B(i32, T) {
+  fn F() { Print("4"); }
+}
+impl forall [T:! type] A(i32, i32) as B(T, i32) {
+  fn F() { Print("3"); }
+}
+
+impl forall [T:! type, U:! type] A(T, i32*) as B(i32*, U) {
+  fn F() { Print("5"); }
+}
+impl forall [T:! type, U:! type] A(i32*, T) as B(U, i32*) {
+  fn F() { Print("6"); }
+}
+
+fn Main() -> i32 {
+  A((), i32).(B(i32, i32).F)();
+  A(i32, ()).(B(i32, i32).F)();
+  A(i32, i32).(B((), i32).F)();
+  A(i32, i32).(B(i32, ()).F)();
+
+  A(i32, i32).(B(i32, i32).F)();
+
+  A(i32*, i32*).(B(i32, i32*).F)();
+  A(i32*, i32*).(B(i32*, i32).F)();
+  A(i32*, i32*).(B(i32*, i32*).F)();
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/fc82ae870beedef35e5a93dbcc561de9224b2809 b/toolchain/semantics/fuzzer_corpus/fc82ae870beedef35e5a93dbcc561de9224b2809
new file mode 100644
index 000000000000..955e63350abd
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/fc82ae870beedef35e5a93dbcc561de9224b2809
@@ -0,0 +1,22 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+class Point {
+  fn Origin() -> Point {
+    return {.x = 0, .y = 0};
+  }
+
+  var x: i32;
+  var y: i32;
+}
+
+fn Main() -> i32 {
+  var p: Point = Point.Origin();
+  return p.Origin().x;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/feeca4b33699f31e73d11b425ebb9b3d0ceced81 b/toolchain/semantics/fuzzer_corpus/feeca4b33699f31e73d11b425ebb9b3d0ceced81
new file mode 100644
index 000000000000..7492c25b4a8a
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/feeca4b33699f31e73d11b425ebb9b3d0ceced81
@@ -0,0 +1,16 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+// Test empty parameters and return type
+fn f() { }
+
+fn Main() -> i32 {
+  f();
+  return 0;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/fef2019d504daf04cb84fea614dd22be3b112ab2 b/toolchain/semantics/fuzzer_corpus/fef2019d504daf04cb84fea614dd22be3b112ab2
new file mode 100644
index 000000000000..66d0e4978fad
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/fef2019d504daf04cb84fea614dd22be3b112ab2
@@ -0,0 +1,17 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: result: 3
+
+package Foo api;
+
+class X {
+  fn F[self: Self](o: Self) -> Self { return {.n = self.n + o.n}; }
+  var n: i32;
+}
+
+fn Main() -> i32 {
+  return {.n = 1}.(X.F)({.n = 2}).n;
+}
diff --git a/toolchain/semantics/fuzzer_corpus/ffeaa3f2403ef6e7b1654d437b2417d9913c332e b/toolchain/semantics/fuzzer_corpus/ffeaa3f2403ef6e7b1654d437b2417d9913c332e
new file mode 100644
index 000000000000..c65e1bfc11ad
--- /dev/null
+++ b/toolchain/semantics/fuzzer_corpus/ffeaa3f2403ef6e7b1654d437b2417d9913c332e
@@ -0,0 +1,30 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// CHECK:STDOUT: (*c).a: 1
+// CHECK:STDOUT: Foo(&d): 1
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+base class C {
+  var a: i32;
+}
+
+class D {
+  extend base: C;
+}
+
+fn Foo(c: C*) -> i32 {
+  return (*c).a;
+}
+
+fn Main() -> i32 {
+  var d: D = { .base = {.a = 1} };
+  var c: C* = &d;
+  Print("(*c).a: {0}", (*c).a);
+  Print("Foo(&d): {0}", Foo(&d));
+  return 0;
+}
diff --git a/toolchain/semantics/semantics_fuzzer.cpp b/toolchain/semantics/semantics_fuzzer.cpp
new file mode 100644
index 000000000000..24400ec7ef77
--- /dev/null
+++ b/toolchain/semantics/semantics_fuzzer.cpp
@@ -0,0 +1,41 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+#include "llvm/ADT/StringRef.h"
+#include "llvm/Support/MemoryBuffer.h"
+#include "llvm/Support/VirtualFileSystem.h"
+#include "toolchain/driver/driver.h"
+
+namespace Carbon::Testing {
+
+// NOLINTNEXTLINE: Match the documented fuzzer entry point declaration style.
+extern "C" int LLVMFuzzerTestOneInput(const unsigned char* data,
+                                      std::size_t size) {
+  // Ignore large inputs.
+  // TODO: See tokenized_buffer_fuzzer.cpp.
+  if (size > 100000) {
+    return 0;
+  }
+
+  static constexpr llvm::StringLiteral TestFileName = "test.carbon";
+  llvm::vfs::InMemoryFileSystem fs;
+  llvm::StringRef data_ref(reinterpret_cast<const char*>(data), size);
+  CARBON_CHECK(fs.addFile(
+      TestFileName, /*ModificationTime=*/0,
+      llvm::MemoryBuffer::getMemBuffer(data_ref, /*BufferName=*/TestFileName,
+                                       /*RequiresNullTerminator=*/false)));
+
+  llvm::raw_null_ostream null_ostream;
+  Driver driver(fs, null_ostream, null_ostream);
+
+  // TODO: Get semantics-ir to a point where it can handle invalid parse trees
+  // without crashing.
+  if (!driver.RunFullCommand({"dump", "parse-tree", TestFileName})) {
+    return 0;
+  }
+  driver.RunFullCommand({"dump", "semantics-ir", TestFileName});
+  return 0;
+}
+
+}  // namespace Carbon::Testing