Boaz Brickner 1ac1d11063 C++ Interop: Support reference types in fields and globals (#6187) ...

Implemented by generalizing the reference type support for parameters
and return values to other use cases.
The changes to the `method.carbon` test are due to to supporting the
reference types but not supporting the necessary conversions.

C++ Interop Demo:

```c++
// global.h

struct C {
  int member = 0;
  int& member_ref = member;
};

extern C& global;
```

```c++
// global.cpp

#include "global.h"

static C static_c;

C& global= static_c;
```

```carbon
// main.carbon

library "Main";

import Core library "io";

import Cpp library "global.h";

fn Run() -> i32 {
  Core.Print(Cpp.global->member);
  ++(*Cpp.global->member_ref);
  Core.Print(Cpp.global->member);
  ++(*Cpp.global->member_ref);
  Core.Print(Cpp.global->member);
  return 0;
}
```

```shell
$ clang++ -stdlib=libc++ -c global.cpp
$ bazel build toolchain:carbon && bazel-bin/toolchain/carbon compile main.carbon
$ bazel-bin/toolchain/carbon link global.o main.o --output=demo
$ ./demo
0
1
2
```

**Without this change**:
```shell
main.carbon:10:14: error: semantics TODO: `Unsupported: var type: C &`
  Core.Print(Cpp.global->member);
             ^~~~~~~~~~
main.carbon:10:14: note: in `Cpp` name lookup for `global`
  Core.Print(Cpp.global->member);
             ^~~~~~~~~~
```

Part of #6006 and #6186.

2025-10-10 23:15:31 +00:00

..

cpp

C++ Interop: Support reference types in fields and globals (#6187)

2025-10-10 23:15:31 +00:00