From bbf896e16558f78b160d8da207db4208d801b6da Mon Sep 17 00:00:00 2001
From: Jon Ross-Perkins <jperkins@google.com>
Date: Wed, 26 Jul 2023 14:30:28 -0700
Subject: [PATCH] Convert returned associated constants. (#3029)

Associated constants were getting returned directly, crashing because
the value InterpProgram received was an AssociatedConstant instead of an
IntValue. We have a similar Convert call in ReturnVar, so I _think_ this
is the right approach.
---
 explorer/interpreter/interpreter.cpp          | 10 ++++---
 .../return/convert_return_assoc.carbon        | 27 +++++++++++++++++++
 2 files changed, 34 insertions(+), 3 deletions(-)
 create mode 100644 explorer/testdata/return/convert_return_assoc.carbon

diff --git a/explorer/interpreter/interpreter.cpp b/explorer/interpreter/interpreter.cpp
index 52eec8114663..f9c7d6587fb5 100644
--- a/explorer/interpreter/interpreter.cpp
+++ b/explorer/interpreter/interpreter.cpp
@@ -2526,12 +2526,16 @@ auto Interpreter::StepStmt() -> ErrorOr<Success> {
         //    { {v :: return [] :: C, E, F} :: {C', E', F'} :: S, H}
         // -> { {v :: C', E', F'} :: S, H}
         const CallableDeclaration& function = cast<Return>(stmt).function();
+        CARBON_ASSIGN_OR_RETURN(
+            Nonnull<const Value*> return_value,
+            Convert(act.results()[0], &function.return_term().static_type(),
+                    stmt.source_loc()));
         // Write to initialized storage location, if any.
         if (const auto location = act.location_received()) {
-          CARBON_RETURN_IF_ERROR(heap_.Write(
-              Address(*location), act.results()[0], stmt.source_loc()));
+          CARBON_RETURN_IF_ERROR(
+              heap_.Write(Address(*location), return_value, stmt.source_loc()));
         }
-        return todo_.UnwindPast(*function.body(), act.results()[0]);
+        return todo_.UnwindPast(*function.body(), return_value);
       }
   }
 }
diff --git a/explorer/testdata/return/convert_return_assoc.carbon b/explorer/testdata/return/convert_return_assoc.carbon
new file mode 100644
index 000000000000..c62c2c1fa48e
--- /dev/null
+++ b/explorer/testdata/return/convert_return_assoc.carbon
@@ -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: 1
+
+package ExplorerTest api;
+
+interface I {
+  let Assoc:! i32;
+}
+
+class C {
+  impl Self as I where .Assoc = 1 {}
+}
+
+alias A = I where .Assoc == 1;
+
+fn F[T:! A](x: T) -> i32 {
+  return x.(A.Assoc);
+}
+
+fn Main() -> i32 {
+  var a: C = {};
+  return F(a);
+}