Diagnose uses of declarations that are too early. (#2288)

There are lots of ways a declaration can be used before we have the information necessary to handle that use. Issue diagnostics for these.

Interleave declaration and type-checking of global declarations so that declaring a later declaration can depend on the results of type-checking an earlier one.

Incorporates tests added in #2266.

Fixes #1394, fixes #1395, fixes #1396.

Co-authored-by: pmqtt <51272730+pmqtt@users.noreply.github.com>
Co-authored-by: Jon Ross-Perkins <jperkins@google.com>

explorer/testdata/function/fail_call_undefined.carbon

@@ -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
+//
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// AUTOUPDATE: %{explorer} %s
+
+package ExplorerTest api;
+
+fn F() -> i32;
+
+fn Main() -> i32 {
+  // CHECK:STDERR: RUNTIME ERROR: {{.*}}/explorer/testdata/function/fail_call_undefined.carbon:[[@LINE+1]]: attempt to call function `F` that has not been defined
+  return F();
+}

explorer/testdata/function/fail_call_undefined_main.carbon

@@ -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
+//
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// AUTOUPDATE: %{explorer} %s
+// CHECK:STDERR: RUNTIME ERROR: <Main()>:0: attempt to call function `Main` that has not been defined
+
+package ExplorerTest api;
+
+fn Main() -> i32;

explorer/testdata/function/fail_invalid_fnty.carbon

@@ -8,10 +8,8 @@
 
 package ExplorerTest api;
 
-// TODO: We should type-check the prelude before the main input so that we can
-// use it within the types of top-level declarations.
 // CHECK:STDERR: COMPILATION ERROR: {{.*}}/explorer/testdata/function/fail_invalid_fnty.carbon:[[@LINE+2]]: type error in `-`:
-// CHECK:STDERR: missing declaration for builtin `Negate`
+// CHECK:STDERR: could not find implementation of interface Negate for bool
 fn f(g: __Fn(-true) -> true) {
 }
 

explorer/testdata/function/fail_recurse_before_typecheck.carbon

@@ -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
+//
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// AUTOUPDATE: %{explorer} %s
+
+package ExplorerTest api;
+
+fn T() -> Type {
+  // CHECK:STDERR: COMPILATION ERROR: {{.*}}/explorer/testdata/function/fail_recurse_before_typecheck.carbon:[[@LINE+1]]: attempt to call function `T` that has not been fully type-checked
+  var v: T() = 0;
+  return i32;
+}
+
+fn Main() -> i32 {
+  return 0;
+}

explorer/testdata/function/fail_recurse_in_return_type.carbon

@@ -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
+//
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// AUTOUPDATE: %{explorer} %s
+
+package ExplorerTest api;
+
+// CHECK:STDERR: COMPILATION ERROR: {{.*}}/explorer/testdata/function/fail_recurse_in_return_type.carbon:[[@LINE+1]]: 'T' is not usable until after it has been completely declared
+fn T() -> T() { return i32; }
+
+fn Main() -> i32 {
+  return 0;
+}

explorer/testdata/function/fail_return_call_has_invalid_body.carbon

@@ -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
+//
+// RUN: %{not} %{explorer} %s 2>&1 2>&1 | %{FileCheck} %s
+// AUTOUPDATE: %{explorer} %s
+
+package EmptyIdentifier impl;
+
+fn apply[T:! Type, U:! Type](f: T, EmptyIdentifier: U) {
+  // CHECK:STDERR: COMPILATION ERROR: {{.*}}/explorer/testdata/function/fail_return_call_has_invalid_body.carbon:[[@LINE+1]]: expected a tuple
+  match (true[true]) {}
+}
+
+fn EmptyIdentifier() -> apply(true, true);
+
+fn Main() -> i32 {
+  return 0;
+}

explorer/testdata/function/fail_var_type_is_call.carbon

@@ -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
+//
+// RUN: %{not} %{explorer} %s 2>&1 2>&1 | %{FileCheck} %s
+// AUTOUPDATE: %{explorer} %s
+
+package EmptyIdentifier impl;
+
+fn test() -> i32 {
+  return 1;
+}
+
+fn Main() -> i32 {
+  // CHECK:STDERR: COMPILATION ERROR: {{.*}}/explorer/testdata/function/fail_var_type_is_call.carbon:[[@LINE+1]]: Expected a type, but got 1
+  var x: test() = 1;
+  return 0;
+}