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carbon-lang/toolchain/lower/testdata/interop/cpp/enum.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/full.carbon
//
// AUTOUPDATE
// TIP: To test this file alone, run:
// TIP: bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/lower/testdata/interop/cpp/enum.carbon
// TIP: To dump output, run:
// TIP: bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/lower/testdata/interop/cpp/enum.carbon
// TODO: Tests marked as `fail_todo_5891_` to fixed as a follow-up of https://github.com/carbon-language/carbon-lang/pull/5891.
// --- enum_member.h
struct C {
enum E : short {
a,
b = 7,
c
};
static void F(E);
};
// --- fail_todo_5891_pass_as_arg.carbon
library "[[@TEST_NAME]]";
import Cpp library "enum_member.h";
fn Pass() {
Cpp.C.F(Cpp.C.a);
// CHECK:STDERR: fail_todo_5891_pass_as_arg.carbon:[[@LINE+7]]:3: error: no matching function for call to `F` [CppOverloadingNoViableFunctionFound]
// CHECK:STDERR: Cpp.C.F(Cpp.C.b);
// CHECK:STDERR: ^~~~~~~~~~~~~~~~
// CHECK:STDERR: fail_todo_5891_pass_as_arg.carbon:[[@LINE+4]]:3: note: in call to Cpp function here [InCallToCppFunction]
// CHECK:STDERR: Cpp.C.F(Cpp.C.b);
// CHECK:STDERR: ^~~~~~~~~~~~~~~~
// CHECK:STDERR:
Cpp.C.F(Cpp.C.b);
// CHECK:STDERR: fail_todo_5891_pass_as_arg.carbon:[[@LINE+7]]:3: error: no matching function for call to `F` [CppOverloadingNoViableFunctionFound]
// CHECK:STDERR: Cpp.C.F(Cpp.C.c);
// CHECK:STDERR: ^~~~~~~~~~~~~~~~
// CHECK:STDERR: fail_todo_5891_pass_as_arg.carbon:[[@LINE+4]]:3: note: in call to Cpp function here [InCallToCppFunction]
// CHECK:STDERR: Cpp.C.F(Cpp.C.c);
// CHECK:STDERR: ^~~~~~~~~~~~~~~~
// CHECK:STDERR:
Cpp.C.F(Cpp.C.c);
// CHECK:STDERR: fail_todo_5891_pass_as_arg.carbon:[[@LINE+7]]:3: error: no matching function for call to `F` [CppOverloadingNoViableFunctionFound]
// CHECK:STDERR: Cpp.C.F(Cpp.C.E.a);
// CHECK:STDERR: ^~~~~~~~~~~~~~~~~~
// CHECK:STDERR: fail_todo_5891_pass_as_arg.carbon:[[@LINE+4]]:3: note: in call to Cpp function here [InCallToCppFunction]
// CHECK:STDERR: Cpp.C.F(Cpp.C.E.a);
// CHECK:STDERR: ^~~~~~~~~~~~~~~~~~
// CHECK:STDERR:
Cpp.C.F(Cpp.C.E.a);
// CHECK:STDERR: fail_todo_5891_pass_as_arg.carbon:[[@LINE+7]]:3: error: no matching function for call to `F` [CppOverloadingNoViableFunctionFound]
// CHECK:STDERR: Cpp.C.F(Cpp.C.E.b);
// CHECK:STDERR: ^~~~~~~~~~~~~~~~~~
// CHECK:STDERR: fail_todo_5891_pass_as_arg.carbon:[[@LINE+4]]:3: note: in call to Cpp function here [InCallToCppFunction]
// CHECK:STDERR: Cpp.C.F(Cpp.C.E.b);
// CHECK:STDERR: ^~~~~~~~~~~~~~~~~~
// CHECK:STDERR:
Cpp.C.F(Cpp.C.E.b);
// CHECK:STDERR: fail_todo_5891_pass_as_arg.carbon:[[@LINE+7]]:3: error: no matching function for call to `F` [CppOverloadingNoViableFunctionFound]
// CHECK:STDERR: Cpp.C.F(Cpp.C.E.c);
// CHECK:STDERR: ^~~~~~~~~~~~~~~~~~
// CHECK:STDERR: fail_todo_5891_pass_as_arg.carbon:[[@LINE+4]]:3: note: in call to Cpp function here [InCallToCppFunction]
// CHECK:STDERR: Cpp.C.F(Cpp.C.E.c);
// CHECK:STDERR: ^~~~~~~~~~~~~~~~~~
// CHECK:STDERR:
Cpp.C.F(Cpp.C.E.c);
}
// --- fail_todo_5891_convert.carbon
library "[[@TEST_NAME]]";
import Cpp library "enum_member.h";
fn TakeI16(n: i16);
fn PassEnum() {
TakeI16(Cpp.C.b as i16);
}
fn ConvertEnumToI16(e: Cpp.C.E) {
TakeI16(e as i16);
}
fn ConvertI16ToEnum(n: i16) {
// CHECK:STDERR: fail_todo_5891_convert.carbon:[[@LINE+7]]:3: error: no matching function for call to `F` [CppOverloadingNoViableFunctionFound]
// CHECK:STDERR: Cpp.C.F(n as Cpp.C.E);
// CHECK:STDERR: ^~~~~~~~~~~~~~~~~~~~~
// CHECK:STDERR: fail_todo_5891_convert.carbon:[[@LINE+4]]:3: note: in call to Cpp function here [InCallToCppFunction]
// CHECK:STDERR: Cpp.C.F(n as Cpp.C.E);
// CHECK:STDERR: ^~~~~~~~~~~~~~~~~~~~~
// CHECK:STDERR:
Cpp.C.F(n as Cpp.C.E);
}
// --- bitmask.h
enum Bits {
A = 1 << 0,
B = 1 << 1,
C = 1 << 2,
};
void Take(Bits b);
// --- fail_todo_use_5891_bitmask.carbon
library "[[@TEST_NAME]]";
import Cpp library "bitmask.h";
// TODO: Once we support interop with C++-defined operators, we should be able
// to use `|` below rather than declaring our own builtin.
fn BitOr(a: Cpp.Bits, b: Cpp.Bits) -> Cpp.Bits = "int.or";
fn Call() {
// CHECK:STDERR: fail_todo_use_5891_bitmask.carbon:[[@LINE+7]]:3: error: no matching function for call to `Take` [CppOverloadingNoViableFunctionFound]
// CHECK:STDERR: Cpp.Take(BitOr(Cpp.A, Cpp.C));
// CHECK:STDERR: ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
// CHECK:STDERR: fail_todo_use_5891_bitmask.carbon:[[@LINE+4]]:3: note: in call to Cpp function here [InCallToCppFunction]
// CHECK:STDERR: Cpp.Take(BitOr(Cpp.A, Cpp.C));
// CHECK:STDERR: ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
// CHECK:STDERR:
Cpp.Take(BitOr(Cpp.A, Cpp.C));
}
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