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carbon-lang/toolchain/check/testdata/interop/cpp/inline.carbon
T
Ivana Ivanovska 12ddfb9c7c [Carbon/C++ interop] Add support for C++ overloaded functions (#5891) 
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
2025-09-15 12:29:49 +00:00

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// 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/none.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/inline.carbon
// TIP: To dump output, run:
// TIP: bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/inline.carbon
// --- use_inline_function_decl.carbon
library "[[@TEST_NAME]]";
//@dump-sem-ir-begin
import Cpp inline '''
// A C++ function.
inline void func() {}
''';
//@dump-sem-ir-end
fn Run() {
//@dump-sem-ir-begin
Cpp.func();
//@dump-sem-ir-end
}
// --- with_language_marker.carbon
library "[[@TEST_NAME]]";
//@dump-sem-ir-begin
import Cpp inline '''c++
// A C++ function.
inline void another_func() {}
''';
//@dump-sem-ir-end
fn Run() {
//@dump-sem-ir-begin
Cpp.another_func();
//@dump-sem-ir-end
}
// CHECK:STDOUT: --- use_inline_function_decl.carbon
// CHECK:STDOUT:
// CHECK:STDOUT: constants {
// CHECK:STDOUT: %empty_tuple.type: type = tuple_type () [concrete]
// CHECK:STDOUT: %.19f: type = cpp_overload_set_type @func [concrete]
// CHECK:STDOUT: %empty_struct: %.19f = struct_value () [concrete]
// CHECK:STDOUT: %func.type: type = fn_type @func [concrete]
// CHECK:STDOUT: %func: %func.type = struct_value () [concrete]
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: imports {
// CHECK:STDOUT: %Cpp: <namespace> = namespace file.%Cpp.import_cpp, [concrete] {
// CHECK:STDOUT: .func = %.ddc
// CHECK:STDOUT: import Cpp//...
// CHECK:STDOUT: }
// CHECK:STDOUT: %.ddc: %.19f = cpp_overload_set_value @func [concrete = constants.%empty_struct]
// CHECK:STDOUT: %func.decl: %func.type = fn_decl @func [concrete = constants.%func] {} {}
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: file {
// CHECK:STDOUT: %Cpp.import_cpp = import_cpp {
// CHECK:STDOUT: import Cpp inline
// CHECK:STDOUT: }
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: fn @Run() {
// CHECK:STDOUT: !entry:
// CHECK:STDOUT: %Cpp.ref: <namespace> = name_ref Cpp, imports.%Cpp [concrete = imports.%Cpp]
// CHECK:STDOUT: %func.ref: %.19f = name_ref func, imports.%.ddc [concrete = constants.%empty_struct]
// CHECK:STDOUT: %func.call: init %empty_tuple.type = call imports.%func.decl()
// CHECK:STDOUT: <elided>
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: --- with_language_marker.carbon
// CHECK:STDOUT:
// CHECK:STDOUT: constants {
// CHECK:STDOUT: %empty_tuple.type: type = tuple_type () [concrete]
// CHECK:STDOUT: %.bcd: type = cpp_overload_set_type @another_func [concrete]
// CHECK:STDOUT: %empty_struct: %.bcd = struct_value () [concrete]
// CHECK:STDOUT: %another_func.type: type = fn_type @another_func [concrete]
// CHECK:STDOUT: %another_func: %another_func.type = struct_value () [concrete]
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: imports {
// CHECK:STDOUT: %Cpp: <namespace> = namespace file.%Cpp.import_cpp, [concrete] {
// CHECK:STDOUT: .another_func = %.b52
// CHECK:STDOUT: import Cpp//...
// CHECK:STDOUT: }
// CHECK:STDOUT: %.b52: %.bcd = cpp_overload_set_value @another_func [concrete = constants.%empty_struct]
// CHECK:STDOUT: %another_func.decl: %another_func.type = fn_decl @another_func [concrete = constants.%another_func] {} {}
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: file {
// CHECK:STDOUT: %Cpp.import_cpp = import_cpp {
// CHECK:STDOUT: import Cpp inline
// CHECK:STDOUT: }
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: fn @Run() {
// CHECK:STDOUT: !entry:
// CHECK:STDOUT: %Cpp.ref: <namespace> = name_ref Cpp, imports.%Cpp [concrete = imports.%Cpp]
// CHECK:STDOUT: %another_func.ref: %.bcd = name_ref another_func, imports.%.b52 [concrete = constants.%empty_struct]
// CHECK:STDOUT: %another_func.call: init %empty_tuple.type = call imports.%another_func.decl()
// CHECK:STDOUT: <elided>
// CHECK:STDOUT: }
// CHECK:STDOUT:
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