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C++ interop: Add return reference types support (#6178)

Browse Source 
This is a follow up of #6082, which added support for reference types,
but not for return types.

C++ Interop Demo:

```carbon
// main.carbon

library "Main";

import Core library "io";

import Cpp inline '''
struct C {
  auto Inc() -> void { ++x; }
  int x = 0;
};
auto GetC() -> C& {
  static C c;
  return c;
}
''';

fn Run() -> i32 {
  Core.Print(Cpp.GetC()->x);
  Cpp.GetC()->Inc();
  Core.Print(Cpp.GetC()->x);
  Cpp.GetC()->Inc();
  Core.Print(Cpp.GetC()->x);
  return 0;
}
```

```shell
$ bazel build toolchain:carbon && bazel-bin/toolchain/carbon compile main.carbon && bazel-bin/toolchain/carbon link main.o --output=demo && ./demo
0
1
2
```

**Without this change**:
```shell
main.carbon:19:14: error: semantics TODO: `Unsupported: return type: C &`
  Core.Print(Cpp.GetC()->x);
             ^~~~~~~~~~
```

Part of #6148.
This commit is contained in:
Boaz Brickner
2025-10-08 16:33:09 +00:00
committed by GitHub
parent ba8ed99eb0
commit bfc4d2b127
4 changed files with 268 additions and 111 deletions
Download Patch File Download Diff File Expand all files Collapse all files
toolchain/check/testdata/interop/cpp/function/reference.carbon
Vendored
+84 -66
View File
@@ -223,22 +223,20 @@ fn F() {
// Lvalue reference as return type
// ============================================================================
// --- fail_todo_call_return_lvalue_ref.carbon
// --- return_lvalue_ref.h
library "[[@TEST_NAME]]";
import Cpp inline '''
struct S {};
auto ReturnsLValue() -> S&;
''';
// --- call_return_lvalue_ref.carbon
library "[[@TEST_NAME]]";
import Cpp library "return_lvalue_ref.h";
fn F() {
//@dump-sem-ir-begin
// CHECK:STDERR: fail_todo_call_return_lvalue_ref.carbon:[[@LINE+4]]:19: error: semantics TODO: `Unsupported: return type: S &` [SemanticsTodo]
// CHECK:STDERR: let s: Cpp.S* = Cpp.ReturnsLValue();
// CHECK:STDERR: ^~~~~~~~~~~~~~~~~~~
// CHECK:STDERR:
let s: Cpp.S* = Cpp.ReturnsLValue();
//@dump-sem-ir-end
}
@@ -247,22 +245,20 @@ fn F() {
// Rvalue reference as return type
// ============================================================================
// --- fail_todo_call_return_rvalue_ref.carbon
// --- return_rvalue_ref.h
library "[[@TEST_NAME]]";
import Cpp inline '''
struct S {};
auto ReturnsRValue() -> S&&;
''';
// --- call_return_rvalue_ref.carbon
library "[[@TEST_NAME]]";
import Cpp library "return_rvalue_ref.h";
fn F() {
//@dump-sem-ir-begin
// CHECK:STDERR: fail_todo_call_return_rvalue_ref.carbon:[[@LINE+4]]:18: error: semantics TODO: `Unsupported: return type: S &&` [SemanticsTodo]
// CHECK:STDERR: var s: Cpp.S = Cpp.ReturnsRValue();
// CHECK:STDERR: ^~~~~~~~~~~~~~~~~~~
// CHECK:STDERR:
var s: Cpp.S = Cpp.ReturnsRValue();
//@dump-sem-ir-end
}
@@ -271,26 +267,41 @@ fn F() {
// Const reference as return type
// ============================================================================
// --- fail_todo_call_return_const_lvalue_ref.carbon
// --- return_const_lvalue_ref.h
library "[[@TEST_NAME]]";
import Cpp inline '''
struct S {};
auto ReturnConstLValue() -> const S&;
''';
// --- call_return_const_lvalue_ref.carbon
library "[[@TEST_NAME]]";
import Cpp library "return_const_lvalue_ref.h";
fn F() {
//@dump-sem-ir-begin
// CHECK:STDERR: fail_todo_call_return_const_lvalue_ref.carbon:[[@LINE+4]]:24: error: semantics TODO: `Unsupported: return type: const S &` [SemanticsTodo]
// CHECK:STDERR: var s: const Cpp.S = Cpp.ReturnConstLValue();
// CHECK:STDERR: ^~~~~~~~~~~~~~~~~~~~~~~
// CHECK:STDERR:
var s: const Cpp.S = Cpp.ReturnConstLValue();
var s: const Cpp.S* = Cpp.ReturnConstLValue();
//@dump-sem-ir-end
}
// --- fail_call_return_const_lvalue_ref_const_correctness.carbon
library "[[@TEST_NAME]]";
import Cpp library "return_const_lvalue_ref.h";
fn F() {
// CHECK:STDERR: fail_call_return_const_lvalue_ref_const_correctness.carbon:[[@LINE+7]]:3: error: cannot implicitly convert expression of type `const Cpp.S*` to `Cpp.S*` [ConversionFailure]
// CHECK:STDERR: var s: Cpp.S* = Cpp.ReturnConstLValue();
// CHECK:STDERR: ^~~~~~~~~~~~~
// CHECK:STDERR: fail_call_return_const_lvalue_ref_const_correctness.carbon:[[@LINE+4]]:3: note: type `const Cpp.S*` does not implement interface `Core.ImplicitAs(Cpp.S*)` [MissingImplInMemberAccessNote]
// CHECK:STDERR: var s: Cpp.S* = Cpp.ReturnConstLValue();
// CHECK:STDERR: ^~~~~~~~~~~~~
// CHECK:STDERR:
var s: Cpp.S* = Cpp.ReturnConstLValue();
}
// CHECK:STDOUT: --- call_param_lvalue_ref.carbon
// CHECK:STDOUT:
// CHECK:STDOUT: constants {
@@ -873,7 +884,7 @@ fn F() {
// CHECK:STDOUT: <elided>
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: --- fail_todo_call_return_lvalue_ref.carbon
// CHECK:STDOUT: --- call_return_lvalue_ref.carbon
// CHECK:STDOUT:
// CHECK:STDOUT: constants {
// CHECK:STDOUT: %S: type = class_type @S [concrete]
@@ -905,19 +916,21 @@ fn F() {
// CHECK:STDOUT: name_binding_decl {
// CHECK:STDOUT: %s.patt: %pattern_type = binding_pattern s [concrete]
// CHECK:STDOUT: }
// CHECK:STDOUT: %Cpp.ref.loc16_19: <namespace> = name_ref Cpp, imports.%Cpp [concrete = imports.%Cpp]
// CHECK:STDOUT: %Cpp.ref.loc8_19: <namespace> = name_ref Cpp, imports.%Cpp [concrete = imports.%Cpp]
// CHECK:STDOUT: %ReturnsLValue.ref: %ReturnsLValue.cpp_overload_set.type = name_ref ReturnsLValue, imports.%ReturnsLValue.cpp_overload_set.value [concrete = constants.%ReturnsLValue.cpp_overload_set.value]
// CHECK:STDOUT: %ReturnsLValue.call: init <error> = call imports.%ReturnsLValue.decl()
// CHECK:STDOUT: %.loc16: type = splice_block %ptr [concrete = constants.%ptr] {
// CHECK:STDOUT: %Cpp.ref.loc16_10: <namespace> = name_ref Cpp, imports.%Cpp [concrete = imports.%Cpp]
// CHECK:STDOUT: %ReturnsLValue.call: init %ptr = call imports.%ReturnsLValue.decl()
// CHECK:STDOUT: %.loc8_15: type = splice_block %ptr [concrete = constants.%ptr] {
// CHECK:STDOUT: %Cpp.ref.loc8_10: <namespace> = name_ref Cpp, imports.%Cpp [concrete = imports.%Cpp]
// CHECK:STDOUT: %S.ref: type = name_ref S, imports.%S.decl [concrete = constants.%S]
// CHECK:STDOUT: %ptr: type = ptr_type %S.ref [concrete = constants.%ptr]
// CHECK:STDOUT: }
// CHECK:STDOUT: %s: %ptr = bind_name s, <error> [concrete = <error>]
// CHECK:STDOUT: %.loc8_37.1: %ptr = value_of_initializer %ReturnsLValue.call
// CHECK:STDOUT: %.loc8_37.2: %ptr = converted %ReturnsLValue.call, %.loc8_37.1
// CHECK:STDOUT: %s: %ptr = bind_name s, %.loc8_37.2
// CHECK:STDOUT: <elided>
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: --- fail_todo_call_return_rvalue_ref.carbon
// CHECK:STDOUT: --- call_return_rvalue_ref.carbon
// CHECK:STDOUT:
// CHECK:STDOUT: constants {
// CHECK:STDOUT: %empty_tuple.type: type = tuple_type () [concrete]
@@ -925,13 +938,13 @@ fn F() {
// CHECK:STDOUT: %pattern_type.7da: type = pattern_type %S [concrete]
// CHECK:STDOUT: %ReturnsRValue.cpp_overload_set.type: type = cpp_overload_set_type @ReturnsRValue.cpp_overload_set [concrete]
// CHECK:STDOUT: %ReturnsRValue.cpp_overload_set.value: %ReturnsRValue.cpp_overload_set.type = cpp_overload_set_value @ReturnsRValue.cpp_overload_set [concrete]
// CHECK:STDOUT: %ReturnsRValue.type: type = fn_type @ReturnsRValue [concrete]
// CHECK:STDOUT: %ReturnsRValue: %ReturnsRValue.type = struct_value () [concrete]
// CHECK:STDOUT: %ptr.5c7: type = ptr_type %S [concrete]
// CHECK:STDOUT: %ReturnsRValue__carbon_thunk.type: type = fn_type @ReturnsRValue__carbon_thunk [concrete]
// CHECK:STDOUT: %ReturnsRValue__carbon_thunk: %ReturnsRValue__carbon_thunk.type = struct_value () [concrete]
// CHECK:STDOUT: %type_where: type = facet_type <type where .Self impls <CanDestroy>> [concrete]
// CHECK:STDOUT: %facet_value: %type_where = facet_value %S, () [concrete]
// CHECK:STDOUT: %DestroyT.binding.as_type.as.Destroy.impl.Op.type.34a: type = fn_type @DestroyT.binding.as_type.as.Destroy.impl.Op, @DestroyT.binding.as_type.as.Destroy.impl(%facet_value) [concrete]
// CHECK:STDOUT: %DestroyT.binding.as_type.as.Destroy.impl.Op.016: %DestroyT.binding.as_type.as.Destroy.impl.Op.type.34a = struct_value () [concrete]
// CHECK:STDOUT: %ptr.5c7: type = ptr_type %S [concrete]
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: imports {
@@ -942,7 +955,7 @@ fn F() {
// CHECK:STDOUT: }
// CHECK:STDOUT: %S.decl: type = class_decl @S [concrete = constants.%S] {} {}
// CHECK:STDOUT: %ReturnsRValue.cpp_overload_set.value: %ReturnsRValue.cpp_overload_set.type = cpp_overload_set_value @ReturnsRValue.cpp_overload_set [concrete = constants.%ReturnsRValue.cpp_overload_set.value]
// CHECK:STDOUT: %ReturnsRValue.decl: %ReturnsRValue.type = fn_decl @ReturnsRValue [concrete = constants.%ReturnsRValue] {
// CHECK:STDOUT: %ReturnsRValue__carbon_thunk.decl: %ReturnsRValue__carbon_thunk.type = fn_decl @ReturnsRValue__carbon_thunk [concrete = constants.%ReturnsRValue__carbon_thunk] {
// CHECK:STDOUT: <elided>
// CHECK:STDOUT: } {
// CHECK:STDOUT: <elided>
@@ -956,41 +969,45 @@ fn F() {
// CHECK:STDOUT: %s.var_patt: %pattern_type.7da = var_pattern %s.patt [concrete]
// CHECK:STDOUT: }
// CHECK:STDOUT: %s.var: ref %S = var %s.var_patt
// CHECK:STDOUT: %Cpp.ref.loc16_18: <namespace> = name_ref Cpp, imports.%Cpp [concrete = imports.%Cpp]
// CHECK:STDOUT: %Cpp.ref.loc8_18: <namespace> = name_ref Cpp, imports.%Cpp [concrete = imports.%Cpp]
// CHECK:STDOUT: %ReturnsRValue.ref: %ReturnsRValue.cpp_overload_set.type = name_ref ReturnsRValue, imports.%ReturnsRValue.cpp_overload_set.value [concrete = constants.%ReturnsRValue.cpp_overload_set.value]
// CHECK:STDOUT: %ReturnsRValue.call: init <error> = call imports.%ReturnsRValue.decl()
// CHECK:STDOUT: assign %s.var, <error>
// CHECK:STDOUT: %.loc16_13: type = splice_block %S.ref [concrete = constants.%S] {
// CHECK:STDOUT: %Cpp.ref.loc16_10: <namespace> = name_ref Cpp, imports.%Cpp [concrete = imports.%Cpp]
// CHECK:STDOUT: %.loc8_3.1: ref %S = splice_block %s.var {}
// CHECK:STDOUT: %addr.loc8_36: %ptr.5c7 = addr_of %.loc8_3.1
// CHECK:STDOUT: %ReturnsRValue__carbon_thunk.call: init %empty_tuple.type = call imports.%ReturnsRValue__carbon_thunk.decl(%addr.loc8_36)
// CHECK:STDOUT: %.loc8_36: init %S = in_place_init %ReturnsRValue__carbon_thunk.call, %.loc8_3.1
// CHECK:STDOUT: assign %s.var, %.loc8_36
// CHECK:STDOUT: %.loc8_13: type = splice_block %S.ref [concrete = constants.%S] {
// CHECK:STDOUT: %Cpp.ref.loc8_10: <namespace> = name_ref Cpp, imports.%Cpp [concrete = imports.%Cpp]
// CHECK:STDOUT: %S.ref: type = name_ref S, imports.%S.decl [concrete = constants.%S]
// CHECK:STDOUT: }
// CHECK:STDOUT: %s: ref %S = bind_name s, %s.var
// CHECK:STDOUT: %facet_value: %type_where = facet_value constants.%S, () [concrete = constants.%facet_value]
// CHECK:STDOUT: %.loc16_3: %type_where = converted constants.%S, %facet_value [concrete = constants.%facet_value]
// CHECK:STDOUT: %.loc8_3.2: %type_where = converted constants.%S, %facet_value [concrete = constants.%facet_value]
// CHECK:STDOUT: %DestroyT.binding.as_type.as.Destroy.impl.Op.bound: <bound method> = bound_method %s.var, constants.%DestroyT.binding.as_type.as.Destroy.impl.Op.016
// CHECK:STDOUT: <elided>
// CHECK:STDOUT: %bound_method: <bound method> = bound_method %s.var, %DestroyT.binding.as_type.as.Destroy.impl.Op.specific_fn
// CHECK:STDOUT: %addr: %ptr.5c7 = addr_of %s.var
// CHECK:STDOUT: %DestroyT.binding.as_type.as.Destroy.impl.Op.call: init %empty_tuple.type = call %bound_method(%addr)
// CHECK:STDOUT: %addr.loc8_3: %ptr.5c7 = addr_of %s.var
// CHECK:STDOUT: %DestroyT.binding.as_type.as.Destroy.impl.Op.call: init %empty_tuple.type = call %bound_method(%addr.loc8_3)
// CHECK:STDOUT: <elided>
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: --- fail_todo_call_return_const_lvalue_ref.carbon
// CHECK:STDOUT: --- call_return_const_lvalue_ref.carbon
// CHECK:STDOUT:
// CHECK:STDOUT: constants {
// CHECK:STDOUT: %empty_tuple.type: type = tuple_type () [concrete]
// CHECK:STDOUT: %S: type = class_type @S [concrete]
// CHECK:STDOUT: %const: type = const_type %S [concrete]
// CHECK:STDOUT: %pattern_type.9be: type = pattern_type %const [concrete]
// CHECK:STDOUT: %ptr.ff5: type = ptr_type %const [concrete]
// CHECK:STDOUT: %pattern_type.32f: type = pattern_type %ptr.ff5 [concrete]
// CHECK:STDOUT: %ReturnConstLValue.cpp_overload_set.type: type = cpp_overload_set_type @ReturnConstLValue.cpp_overload_set [concrete]
// CHECK:STDOUT: %ReturnConstLValue.cpp_overload_set.value: %ReturnConstLValue.cpp_overload_set.type = cpp_overload_set_value @ReturnConstLValue.cpp_overload_set [concrete]
// CHECK:STDOUT: %ReturnConstLValue.type: type = fn_type @ReturnConstLValue [concrete]
// CHECK:STDOUT: %ReturnConstLValue: %ReturnConstLValue.type = struct_value () [concrete]
// CHECK:STDOUT: %type_where: type = facet_type <type where .Self impls <CanDestroy>> [concrete]
// CHECK:STDOUT: %facet_value: %type_where = facet_value %const, () [concrete]
// CHECK:STDOUT: %DestroyT.binding.as_type.as.Destroy.impl.Op.type.56e: type = fn_type @DestroyT.binding.as_type.as.Destroy.impl.Op, @DestroyT.binding.as_type.as.Destroy.impl(%facet_value) [concrete]
// CHECK:STDOUT: %DestroyT.binding.as_type.as.Destroy.impl.Op.089: %DestroyT.binding.as_type.as.Destroy.impl.Op.type.56e = struct_value () [concrete]
// CHECK:STDOUT: %ptr.ff5: type = ptr_type %const [concrete]
// CHECK:STDOUT: %facet_value: %type_where = facet_value %ptr.ff5, () [concrete]
// CHECK:STDOUT: %DestroyT.binding.as_type.as.Destroy.impl.Op.type.40d: type = fn_type @DestroyT.binding.as_type.as.Destroy.impl.Op, @DestroyT.binding.as_type.as.Destroy.impl(%facet_value) [concrete]
// CHECK:STDOUT: %DestroyT.binding.as_type.as.Destroy.impl.Op.c44: %DestroyT.binding.as_type.as.Destroy.impl.Op.type.40d = struct_value () [concrete]
// CHECK:STDOUT: %ptr.dec: type = ptr_type %ptr.ff5 [concrete]
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: imports {
@@ -1011,26 +1028,27 @@ fn F() {
// CHECK:STDOUT: fn @F() {
// CHECK:STDOUT: !entry:
// CHECK:STDOUT: name_binding_decl {
// CHECK:STDOUT: %s.patt: %pattern_type.9be = binding_pattern s [concrete]
// CHECK:STDOUT: %s.var_patt: %pattern_type.9be = var_pattern %s.patt [concrete]
// CHECK:STDOUT: %s.patt: %pattern_type.32f = binding_pattern s [concrete]
// CHECK:STDOUT: %s.var_patt: %pattern_type.32f = var_pattern %s.patt [concrete]
// CHECK:STDOUT: }
// CHECK:STDOUT: %s.var: ref %const = var %s.var_patt
// CHECK:STDOUT: %Cpp.ref.loc16_24: <namespace> = name_ref Cpp, imports.%Cpp [concrete = imports.%Cpp]
// CHECK:STDOUT: %s.var: ref %ptr.ff5 = var %s.var_patt
// CHECK:STDOUT: %Cpp.ref.loc8_25: <namespace> = name_ref Cpp, imports.%Cpp [concrete = imports.%Cpp]
// CHECK:STDOUT: %ReturnConstLValue.ref: %ReturnConstLValue.cpp_overload_set.type = name_ref ReturnConstLValue, imports.%ReturnConstLValue.cpp_overload_set.value [concrete = constants.%ReturnConstLValue.cpp_overload_set.value]
// CHECK:STDOUT: %ReturnConstLValue.call: init <error> = call imports.%ReturnConstLValue.decl()
// CHECK:STDOUT: assign %s.var, <error>
// CHECK:STDOUT: %.loc16_10: type = splice_block %const [concrete = constants.%const] {
// CHECK:STDOUT: %Cpp.ref.loc16_16: <namespace> = name_ref Cpp, imports.%Cpp [concrete = imports.%Cpp]
// CHECK:STDOUT: %ReturnConstLValue.call: init %ptr.ff5 = call imports.%ReturnConstLValue.decl()
// CHECK:STDOUT: assign %s.var, %ReturnConstLValue.call
// CHECK:STDOUT: %.loc8_21: type = splice_block %ptr [concrete = constants.%ptr.ff5] {
// CHECK:STDOUT: %Cpp.ref.loc8_16: <namespace> = name_ref Cpp, imports.%Cpp [concrete = imports.%Cpp]
// CHECK:STDOUT: %S.ref: type = name_ref S, imports.%S.decl [concrete = constants.%S]
// CHECK:STDOUT: %const: type = const_type %S.ref [concrete = constants.%const]
// CHECK:STDOUT: %ptr: type = ptr_type %const [concrete = constants.%ptr.ff5]
// CHECK:STDOUT: }
// CHECK:STDOUT: %s: ref %const = bind_name s, %s.var
// CHECK:STDOUT: %facet_value: %type_where = facet_value constants.%const, () [concrete = constants.%facet_value]
// CHECK:STDOUT: %.loc16_3: %type_where = converted constants.%const, %facet_value [concrete = constants.%facet_value]
// CHECK:STDOUT: %DestroyT.binding.as_type.as.Destroy.impl.Op.bound: <bound method> = bound_method %s.var, constants.%DestroyT.binding.as_type.as.Destroy.impl.Op.089
// CHECK:STDOUT: %s: ref %ptr.ff5 = bind_name s, %s.var
// CHECK:STDOUT: %facet_value: %type_where = facet_value constants.%ptr.ff5, () [concrete = constants.%facet_value]
// CHECK:STDOUT: %.loc8_3: %type_where = converted constants.%ptr.ff5, %facet_value [concrete = constants.%facet_value]
// CHECK:STDOUT: %DestroyT.binding.as_type.as.Destroy.impl.Op.bound: <bound method> = bound_method %s.var, constants.%DestroyT.binding.as_type.as.Destroy.impl.Op.c44
// CHECK:STDOUT: <elided>
// CHECK:STDOUT: %bound_method: <bound method> = bound_method %s.var, %DestroyT.binding.as_type.as.Destroy.impl.Op.specific_fn
// CHECK:STDOUT: %addr: %ptr.ff5 = addr_of %s.var
// CHECK:STDOUT: %addr: %ptr.dec = addr_of %s.var
// CHECK:STDOUT: %DestroyT.binding.as_type.as.Destroy.impl.Op.call: init %empty_tuple.type = call %bound_method(%addr)
// CHECK:STDOUT: <elided>
// CHECK:STDOUT: }