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Handle signature mismatch when a Carbon function overrides a C++ virtual function. (#7499)

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When a Carbon virtual function overrides a C++ virtual function, we need
to export it with the C++ signature in order for it to work as an
override. Instead of mapping the C++ signature into Carbon and then back
again, use the original C++ signature from the base class as the
signature exported to C++.

Also add documentation explaining how we use thunks in C++ interop,
including in this new virtual function handling logic.
This commit is contained in:
Richard Smith
2026-07-15 18:42:03 +00:00
committed by GitHub
parent 14e8bffe24
commit 9ae73d2847
14 changed files with 635 additions and 174 deletions
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toolchain/check/testdata/interop/cpp/function/export/array.carbon
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+1 -11
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@@ -43,16 +43,6 @@ import Cpp;
// 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: ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
@@ -67,7 +57,7 @@ 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: 28 | return Carbon::F({1, 2, 3, 4, 5});
// CHECK:STDERR: | ^
// CHECK:STDERR:
return Carbon::F({1, 2, 3, 4, 5});