Support for mapping array types to/from C++. (#7285)

For now, disable the use of array types as by-var paramters and by-init return types when exporting Carbon functions to C++, as C++ does not support raw arrays being passed or returned by value. Assisted-by: Gemini via Antigravity
2026-10-04 11:51:05 +01:00 · 2026-06-01 21:55:16 +00:00
parent d01e1d2d06
commit 2952f61095
12 changed files with 495 additions and 37 deletions
@@ -0,0 +1,104 @@
+// Part of the Carbon Language 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-FILE: toolchain/testing/testdata/min_prelude/int.carbon
+//
+// AUTOUPDATE
+// TIP: To test this file alone, run:
+// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/function/export/array.carbon
+// TIP: To dump output, run:
+// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/function/export/array.carbon
+
+// --- array_value_param.carbon
+library "[[@TEST_NAME]]";
+
+import Cpp;
+
+fn F(a: array(i32, 5)) -> i32 { return a[2]; }
+
+inline Cpp '''
+int G() {
+  int arr[5];
+  //@dump-sem-ir-begin
+  return Carbon::F(arr);
+  //@dump-sem-ir-end
+}
+
+int H() {
+  //@dump-sem-ir-begin
+  return Carbon::F({1, 2, 3, 4, 5});
+  //@dump-sem-ir-end
+}
+''';
+
+// --- fail_todo_array_var_param.carbon
+library "[[@TEST_NAME]]";
+
+import Cpp;
+
+// We do not currently support C++ calls to functions with by-var array
+// parameters, as C++ does not have such parameters.
+// TODO: Support this, perhaps using Clang's `ArrayParameterType`, which is an
+// HLSL extension, or by mapping to a `std::array` parameter.
+
+// TODO: These diagnostics are very bad.
+// CHECK:STDERR: fail_todo_array_var_param.carbon:[[@LINE+18]]:1: error: cannot copy value of type `array(i32, 5)` [CopyOfUncopyableType]
+// CHECK:STDERR: fn F(var a: array(i32, 5)) -> i32 { return a[2]; }
+// CHECK:STDERR: ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// CHECK:STDERR: fail_todo_array_var_param.carbon:[[@LINE+15]]:1: note: type `array(i32, 5)` does not implement interface `Core.Copy` [MissingImplInMemberAccessInContext]
+// CHECK:STDERR: fn F(var a: array(i32, 5)) -> i32 { return a[2]; }
+// CHECK:STDERR: ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// CHECK:STDERR: fail_todo_array_var_param.carbon:[[@LINE+12]]:6: note: initializing function parameter [InCallToFunctionParam]
+// CHECK:STDERR: fn F(var a: array(i32, 5)) -> i32 { return a[2]; }
+// CHECK:STDERR:      ^~~~~~~~~~~~~~~~~~~~
+// CHECK:STDERR:
+// CHECK:STDERR: fail_todo_array_var_param.carbon:[[@LINE+8]]:1: error: semantics TODO: `by-var array parameter` [SemanticsTodo]
+// CHECK:STDERR: fn F(var a: array(i32, 5)) -> i32 { return a[2]; }
+// CHECK:STDERR: ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// CHECK:STDERR:
+// CHECK:STDERR: fail_todo_array_var_param.carbon:[[@LINE+4]]:1: error: semantics TODO: `failed to map C++ type to Carbon` [SemanticsTodo]
+// CHECK:STDERR: fn F(var a: array(i32, 5)) -> i32 { return a[2]; }
+// CHECK:STDERR: ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// CHECK:STDERR:
+fn F(var a: array(i32, 5)) -> i32 { return a[2]; }
+
+inline Cpp '''
+int G() {
+  //@dump-sem-ir-begin
+  // CHECK:STDERR: fail_todo_array_var_param.carbon:[[@LINE+4]]:18: error: no member named 'F' in namespace 'Carbon' [CppInteropParseError]
+  // CHECK:STDERR:    38 |   return Carbon::F({1, 2, 3, 4, 5});
+  // CHECK:STDERR:       |                  ^
+  // CHECK:STDERR:
+  return Carbon::F({1, 2, 3, 4, 5});
+  //@dump-sem-ir-end
+}
+''';
+
+// --- fail_todo_array_return.carbon
+library "[[@TEST_NAME]]";
+
+import Cpp;
+
+// We do not currently support C++ calls to functions with array return
+// types, as C++ does not have such return types.
+// TODO: Support this, perhaps by returning a `std::array`.
+
+// CHECK:STDERR: fail_todo_array_return.carbon:[[@LINE+4]]:1: error: semantics TODO: `array return type` [SemanticsTodo]
+// CHECK:STDERR: fn F() -> array(i32, 5) {
+// CHECK:STDERR: ^~~~~~~~~~~~~~~~~~~~~~~~~
+// CHECK:STDERR:
+fn F() -> array(i32, 5) {
+  return (1, 2, 3, 4, 5);
+}
+
+inline Cpp '''
+int G() {
+  // CHECK:STDERR: fail_todo_array_return.carbon:[[@LINE+4]]:24: error: no member named 'F' in namespace 'Carbon' [CppInteropParseError]
+  // CHECK:STDERR:    23 |   auto &&arr = Carbon::F();
+  // CHECK:STDERR:       |                        ^
+  // CHECK:STDERR:
+  auto &&arr = Carbon::F();
+  return arr[0];
+}
+''';