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[Carbon/C++ interop] Add support for C++ overloaded functions (#5891)

Browse Source 
As proposed in [Carbon: C++ interop for overloaded functions and
function
templates](https://docs.google.com/document/d/1KUxumZtNe3mY3TsjW2s_ZADOlAaFlrtsLKHVILtqIaM/edit?tab=t.0),
Clang is used to perform the overload resolution using C++ rules, when
an overloaded C++ set is called from Carbon. Once a function is
selected, it's converted into a Carbon function and called using the
Carbon rules including argument conversions.

A single non-templated function is treated the same way as an overload
set and the same rules apply for its call.
Template functions are not supported yet.

Demo:

a) Non-templated function calls:

```c++
// --- overloads.h

auto foo(int a, short b) -> void;
auto foo(double a) -> void;
auto foo(int a) -> void;
```

```c++
// overloads.cpp

#include "overloads.h"
#include <cstdio>

auto foo(int a, short b) -> void {
  printf("hello from foo_int_short(%d, %d) \n", a, b);
}
auto foo(double a) -> void { printf("hello from foo_double(%f) \n", a); }
auto foo(int a) -> void { printf("hello from foo_int(%d) \n", a); }
```
```c++
library "Main";

import Cpp library "overloads.h";

fn Run() -> i32 {
  Cpp.foo(1.1 as f64);
  return 0;
}
```
```
$ clang -c overloads.cpp 
$ bazel-bin/toolchain/carbon compile main.carbon
$ bazel-bin/toolchain/carbon link overloads.o main.o --output=demo
$ ./demo
hello from foo_double(1.100000) 
```

b) Constructors:
```c++
// --- constructor_overloads.h
class C {
 public:
  C();
  C(int a, int b);
};
```

```c++
// constructor_overloads.cpp
#include "constructor_overloads.h"
#include <cstdio>

C::C() { printf("hello from C() \n"); }
C::C(int a, int b) { printf("hello from C(%d, %d) \n", a, b); }
```
```c++
library "Main";

import Cpp library "constructor_overloads.h";

fn Run() -> i32 {
  let c1: Cpp.C = Cpp.C.C();
  let c2: Cpp.C = Cpp.C.C(1, 2);
  return 0;
}
```

```
$ clang -c constructor_overloads.cpp 
$ bazel-bin/toolchain/carbon compile main.carbon
$ bazel-bin/toolchain/carbon link constructor_overloads.o main.o \--output=demo
$ ./demo
hello from C() 
hello from C(1, 2) 
```


Follow-ups:

- `Cpp.foo({})` - proper handling of struct literals as call args.
- Fix access for overloaded sets.
- Fix tests:
- Method calls: `error: missing object argument in method call
[MissingObjectInMethodCall]` in tests.
    - Fix `toolchain/check/testdata/interop/cpp/import.carbon` test.
    - Fix `enums` support.
    - Fix `str` -> `std::string_view` mapping.


Part of #5915
This commit is contained in:
Ivana Ivanovska
2025-09-15 12:29:49 +00:00
committed by GitHub
parent 20ac6b9270
commit 12ddfb9c7c
61 changed files with 4633 additions and 2252 deletions
Download Patch File Download Diff File Expand all files Collapse all files
toolchain/check/testdata/interop/cpp/function/param_unsupported.carbon
Vendored
+16 -10
View File
@@ -28,10 +28,10 @@ fn F() {
//@dump-sem-ir-begin
// CHECK:STDERR: fail_todo_import_unsupported_primitive_type.carbon:[[@LINE+7]]:3: error: semantics TODO: `Unsupported: parameter type: _BitInt(23)` [SemanticsTodo]
// CHECK:STDERR: Cpp.foo(11);
// CHECK:STDERR: ^~~~~~~
// CHECK:STDERR: fail_todo_import_unsupported_primitive_type.carbon:[[@LINE+4]]:3: note: in `Cpp` name lookup for `foo` [InCppNameLookup]
// CHECK:STDERR: ^~~~~~~~~~~
// CHECK:STDERR: fail_todo_import_unsupported_primitive_type.carbon:[[@LINE+4]]:3: note: in call to Cpp function here [InCallToCppFunction]
// CHECK:STDERR: Cpp.foo(11);
// CHECK:STDERR: ^~~~~~~
// CHECK:STDERR: ^~~~~~~~~~~
// CHECK:STDERR:
Cpp.foo(11);
//@dump-sem-ir-end
@@ -55,10 +55,10 @@ fn F() {
//@dump-sem-ir-begin
// CHECK:STDERR: fail_todo_import_unsupported_primitive_type_among_params.carbon:[[@LINE+7]]:3: error: semantics TODO: `Unsupported: parameter type: _BitInt(23)` [SemanticsTodo]
// CHECK:STDERR: Cpp.foo(1, 20);
// CHECK:STDERR: ^~~~~~~
// CHECK:STDERR: fail_todo_import_unsupported_primitive_type_among_params.carbon:[[@LINE+4]]:3: note: in `Cpp` name lookup for `foo` [InCppNameLookup]
// CHECK:STDERR: ^~~~~~~~~~~~~~
// CHECK:STDERR: fail_todo_import_unsupported_primitive_type_among_params.carbon:[[@LINE+4]]:3: note: in call to Cpp function here [InCallToCppFunction]
// CHECK:STDERR: Cpp.foo(1, 20);
// CHECK:STDERR: ^~~~~~~
// CHECK:STDERR: ^~~~~~~~~~~~~~
// CHECK:STDERR:
Cpp.foo(1, 20);
//@dump-sem-ir-end
@@ -67,20 +67,23 @@ fn F() {
// CHECK:STDOUT: --- fail_todo_import_unsupported_primitive_type.carbon
// CHECK:STDOUT:
// CHECK:STDOUT: constants {
// CHECK:STDOUT: %.c5d: type = cpp_overload_set_type @<null name> [concrete]
// CHECK:STDOUT: %empty_struct: %.c5d = struct_value () [concrete]
// CHECK:STDOUT: %int_11: Core.IntLiteral = int_value 11 [concrete]
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: imports {
// CHECK:STDOUT: %Cpp: <namespace> = namespace file.%Cpp.import_cpp, [concrete] {
// CHECK:STDOUT: .foo = <error>
// CHECK:STDOUT: .foo = %.a21
// CHECK:STDOUT: import Cpp//...
// CHECK:STDOUT: }
// CHECK:STDOUT: %.a21: %.c5d = cpp_overload_set_value @<null name> [concrete = constants.%empty_struct]
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: fn @F() {
// CHECK:STDOUT: !entry:
// CHECK:STDOUT: %Cpp.ref: <namespace> = name_ref Cpp, imports.%Cpp [concrete = imports.%Cpp]
// CHECK:STDOUT: %foo.ref: <error> = name_ref foo, <error> [concrete = <error>]
// CHECK:STDOUT: %foo.ref: %.c5d = name_ref foo, imports.%.a21 [concrete = constants.%empty_struct]
// CHECK:STDOUT: %int_11: Core.IntLiteral = int_value 11 [concrete = constants.%int_11]
// CHECK:STDOUT: <elided>
// CHECK:STDOUT: }
@@ -88,21 +91,24 @@ fn F() {
// CHECK:STDOUT: --- fail_todo_import_unsupported_primitive_type_among_params.carbon
// CHECK:STDOUT:
// CHECK:STDOUT: constants {
// CHECK:STDOUT: %.c5d: type = cpp_overload_set_type @<null name> [concrete]
// CHECK:STDOUT: %empty_struct: %.c5d = struct_value () [concrete]
// CHECK:STDOUT: %int_1: Core.IntLiteral = int_value 1 [concrete]
// CHECK:STDOUT: %int_20: Core.IntLiteral = int_value 20 [concrete]
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: imports {
// CHECK:STDOUT: %Cpp: <namespace> = namespace file.%Cpp.import_cpp, [concrete] {
// CHECK:STDOUT: .foo = <error>
// CHECK:STDOUT: .foo = %.a21
// CHECK:STDOUT: import Cpp//...
// CHECK:STDOUT: }
// CHECK:STDOUT: %.a21: %.c5d = cpp_overload_set_value @<null name> [concrete = constants.%empty_struct]
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: fn @F() {
// CHECK:STDOUT: !entry:
// CHECK:STDOUT: %Cpp.ref: <namespace> = name_ref Cpp, imports.%Cpp [concrete = imports.%Cpp]
// CHECK:STDOUT: %foo.ref: <error> = name_ref foo, <error> [concrete = <error>]
// CHECK:STDOUT: %foo.ref: %.c5d = name_ref foo, imports.%.a21 [concrete = constants.%empty_struct]
// CHECK:STDOUT: %int_1: Core.IntLiteral = int_value 1 [concrete = constants.%int_1]
// CHECK:STDOUT: %int_20: Core.IntLiteral = int_value 20 [concrete = constants.%int_20]
// CHECK:STDOUT: <elided>