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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/in_template.carbon
Vendored
+6 -3
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@@ -38,11 +38,13 @@ fn F() {
// CHECK:STDOUT: constants {
// CHECK:STDOUT: %empty_tuple.type: type = tuple_type () [concrete]
// CHECK:STDOUT: %X: type = class_type @X [concrete]
// CHECK:STDOUT: %.034: type = cpp_overload_set_type @X.f [concrete]
// CHECK:STDOUT: %empty_struct: %.034 = struct_value () [concrete]
// CHECK:STDOUT: %int_42.20e: Core.IntLiteral = int_value 42 [concrete]
// CHECK:STDOUT: %int_32: Core.IntLiteral = int_value 32 [concrete]
// CHECK:STDOUT: %i32: type = class_type @Int, @Int(%int_32) [concrete]
// CHECK:STDOUT: %X.f.type: type = fn_type @X.f [concrete]
// CHECK:STDOUT: %X.f: %X.f.type = struct_value () [concrete]
// CHECK:STDOUT: %int_42.20e: Core.IntLiteral = int_value 42 [concrete]
// CHECK:STDOUT: %ImplicitAs.type.e8c: type = facet_type <@ImplicitAs, @ImplicitAs(%i32)> [concrete]
// CHECK:STDOUT: %ImplicitAs.Convert.type.1b6: type = fn_type @ImplicitAs.Convert, @ImplicitAs(%i32) [concrete]
// CHECK:STDOUT: %To: Core.IntLiteral = bind_symbolic_name To, 0 [symbolic]
@@ -65,6 +67,7 @@ fn F() {
// CHECK:STDOUT: import Cpp//...
// CHECK:STDOUT: }
// CHECK:STDOUT: %X.decl: type = class_decl @X [concrete = constants.%X] {} {}
// CHECK:STDOUT: %.a8d: %.034 = cpp_overload_set_value @X.f [concrete = constants.%empty_struct]
// CHECK:STDOUT: %X.f.decl: %X.f.type = fn_decl @X.f [concrete = constants.%X.f] {
// CHECK:STDOUT: <elided>
// CHECK:STDOUT: } {
@@ -78,7 +81,7 @@ fn F() {
// CHECK:STDOUT: !entry:
// CHECK:STDOUT: %Cpp.ref: <namespace> = name_ref Cpp, imports.%Cpp [concrete = imports.%Cpp]
// CHECK:STDOUT: %Y.ref: type = name_ref Y, imports.%X.decl [concrete = constants.%X]
// CHECK:STDOUT: %f.ref: %X.f.type = name_ref f, imports.%X.f.decl [concrete = constants.%X.f]
// CHECK:STDOUT: %f.ref: %.034 = name_ref f, imports.%.a8d [concrete = constants.%empty_struct]
// CHECK:STDOUT: %int_42: Core.IntLiteral = int_value 42 [concrete = constants.%int_42.20e]
// CHECK:STDOUT: %impl.elem0: %.7ea = impl_witness_access constants.%ImplicitAs.impl_witness.acc, element0 [concrete = constants.%Core.IntLiteral.as.ImplicitAs.impl.Convert.592]
// CHECK:STDOUT: %bound_method.loc8_11.1: <bound method> = bound_method %int_42, %impl.elem0 [concrete = constants.%Core.IntLiteral.as.ImplicitAs.impl.Convert.bound]
@@ -87,7 +90,7 @@ fn F() {
// CHECK:STDOUT: %Core.IntLiteral.as.ImplicitAs.impl.Convert.call: init %i32 = call %bound_method.loc8_11.2(%int_42) [concrete = constants.%int_42.c68]
// CHECK:STDOUT: %.loc8_11.1: %i32 = value_of_initializer %Core.IntLiteral.as.ImplicitAs.impl.Convert.call [concrete = constants.%int_42.c68]
// CHECK:STDOUT: %.loc8_11.2: %i32 = converted %int_42, %.loc8_11.1 [concrete = constants.%int_42.c68]
// CHECK:STDOUT: %X.f.call: init %empty_tuple.type = call %f.ref(%.loc8_11.2)
// CHECK:STDOUT: %X.f.call: init %empty_tuple.type = call imports.%X.f.decl(%.loc8_11.2)
// CHECK:STDOUT: <elided>
// CHECK:STDOUT: }
// CHECK:STDOUT: