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Add initial support for exporting generic Carbon functions to C++ (#7462)

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This allows C++ to call Carbon functions with generic type parameters,
with some conditions. Example:
```carbon
interface I {
  fn Doit(self);
}
class A {
  impl as I { fn Doit(unused self) {} }
}
class B {
  impl as I { fn Doit(unused self) {} }
}
fn F[T:! I](t: T) {
  t.Doit();
}

inline Cpp '''
void G() {
  Carbon::A a;
  Carbon::B b;
  Carbon::F(a);
  Carbon::F(b);
}
''';
```

The initial support is limited; only explicit parameters are handled
currently.

`CarbonExternalASTSource::GetOrExportFunctionToCpp` now generates a
`clang::FunctionTemplateDecl` for generic Carbon functions. If C++ code
attempts to call that templated function,
`CarbonExternalASTSource::LoadExternalSpecializations` will be called
with the template argument types of that call site. Then we can generate
a specialized thunk for those argument types for C++ to call.
This commit is contained in:
Nicholas Bishop
2026-07-08 00:51:21 +00:00
committed by GitHub
parent eab71802f7
commit c8fdeef911
7 changed files with 1160 additions and 51 deletions
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toolchain/check/testdata/interop/cpp/function/export/function.carbon
Vendored
+6 -19
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@@ -85,42 +85,29 @@ void G() { F(); }
library "[[@TEST_NAME]]";
// CHECK:STDERR: fail_todo_generic.carbon:[[@LINE+9]]:1: in import [InImport]
// CHECK:STDERR: other.carbon:7:1: error: 1 argument passed to function expecting 2 arguments [CallArgCountMismatch]
// CHECK:STDERR: fn HasGenericArg(T:! type, a: T) { a; }
// CHECK:STDERR: ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
// CHECK:STDERR: fail_todo_generic.carbon:[[@LINE+5]]:1: in import [InImport]
// CHECK:STDERR: other.carbon:7:1: error: semantics TODO: `unsupported: C++ calling a Carbon function with generic parameters` [SemanticsTodo]
// CHECK:STDERR: other.carbon:7:1: note: calling function declared here [InCallToEntity]
// CHECK:STDERR: fn HasGenericArg(T:! type, a: T) { a; }
// CHECK:STDERR: ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
// CHECK:STDERR:
import Other;
import Cpp inline '''
void G() {
// CHECK:STDERR: fail_todo_generic.carbon:[[@LINE+8]]:18: error: no member named 'HasGenericArg' in namespace 'Carbon::Other' [CppInteropParseError]
// CHECK:STDERR: 20 | Carbon::Other::HasGenericArg<int>(123);
// CHECK:STDERR: | ^~~~~~~~~~~~~
// CHECK:STDERR:
// CHECK:STDERR: fail_todo_generic.carbon:[[@LINE+4]]:35: error: expected '(' for function-style cast or type construction [CppInteropParseError]
// CHECK:STDERR: 20 | Carbon::Other::HasGenericArg<int>(123);
// CHECK:STDERR: | ~~~^
// CHECK:STDERR:
Carbon::Other::HasGenericArg<int>(123);
}
''';
// --- fail_todo_deduced.carbon
// --- deduced.carbon
library "[[@TEST_NAME]]";
// CHECK:STDERR: fail_todo_deduced.carbon:[[@LINE+5]]:1: in import [InImport]
// CHECK:STDERR: other.carbon:8:1: error: semantics TODO: `unsupported: C++ calling a Carbon function with generic parameters` [SemanticsTodo]
// CHECK:STDERR: fn HasDeducedArg[T:! type](a: T) { a; }
// CHECK:STDERR: ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
// CHECK:STDERR:
import Other;
import Cpp inline '''
void G() {
// CHECK:STDERR: fail_todo_deduced.carbon:[[@LINE+4]]:18: error: no member named 'HasDeducedArg' in namespace 'Carbon::Other' [CppInteropParseError]
// CHECK:STDERR: 16 | Carbon::Other::HasDeducedArg(123);
// CHECK:STDERR: | ^~~~~~~~~~~~~
// CHECK:STDERR:
Carbon::Other::HasDeducedArg(123);
}
''';