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Add support for using C++ user-defined conversions via interop (#6646)

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When performing an implicit conversion to or from a C++ class type, look
for a C++ implicit conversion, and if that conversion involves a
function call (to a constructor or conversion function), call that
function to perform the conversion.

Note that this is just a first pass at supporting implicit conversions.
There are a lot of other things that can happen in a C++ implicit
conversion, such as aggregate initialization or `std::initializer_list`
initialization that aren't handled here. In addition, we intentionally
leave all standard conversions to Carbon to perform, so that we will
reject conversions such as `i32 -> unsigned` that C++ would select but
Carbon considers to be invalid.

Also support `as` conversions. These are treated analogously, but
perform direct-initialization instead of copy-initialization, so they
also find `explicit` constructors and conversion functions.

In order to give good diagnostics, also track the original C++ source
location for imported C++ functions on the imported version of the
function.

Assisted-by: Gemini 3 Pro via Antigravity
This commit is contained in:
Richard Smith
2026-01-25 04:51:25 +00:00
committed by GitHub
parent 9836ba6e9c
commit 093d5072db
17 changed files with 1947 additions and 363 deletions
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toolchain/check/cpp/import.cpp
+13 -7
View File
@@ -1391,7 +1391,8 @@ static auto GetFunctionName(Context& context, clang::FunctionDecl* clang_decl)
return SemIR::NameId::CppDestructor;
}
case clang::DeclarationName::CXXOperatorName: {
case clang::DeclarationName::CXXOperatorName:
case clang::DeclarationName::CXXConversionFunctionName: {
return SemIR::NameId::CppOperator;
}
@@ -1406,6 +1407,7 @@ static auto GetFunctionName(Context& context, clang::FunctionDecl* clang_decl)
// * Have not been imported before.
// * Be of supported type (ignoring parameters).
static auto ImportFunction(Context& context, SemIR::LocId loc_id,
SemIR::ImportIRInstId import_ir_inst_id,
clang::FunctionDecl* clang_decl, int num_params)
-> std::optional<SemIR::FunctionId> {
context.scope_stack().PushForDeclName();
@@ -1426,7 +1428,8 @@ static auto ImportFunction(Context& context, SemIR::LocId loc_id,
auto function_decl = SemIR::FunctionDecl{
SemIR::TypeId::None, SemIR::FunctionId::None, decl_block_id};
auto decl_id = AddPlaceholderImportedInstInNoBlock(
context, SemIR::LocIdAndInst::NoLoc(function_decl));
context,
MakeImportedLocIdAndInst(context, import_ir_inst_id, function_decl));
auto virtual_modifier = SemIR::Function::VirtualModifier::None;
int32_t virtual_index = -1;
@@ -1506,10 +1509,13 @@ static auto ImportFunctionDecl(Context& context, SemIR::LocId loc_id,
return SemIR::ErrorInst::InstId;
}
auto import_ir_inst_id =
AddImportIRInst(context.sem_ir(), clang_decl->getLocation());
CARBON_CHECK(clang_decl->getFunctionType()->isFunctionProtoType(),
"Not Prototype function (non-C++ code)");
auto function_id = ImportFunction(context, loc_id, clang_decl, num_params);
auto function_id = ImportFunction(context, loc_id, import_ir_inst_id,
clang_decl, num_params);
if (!function_id) {
MarkFailedDecl(context, key);
return SemIR::ErrorInst::InstId;
@@ -1526,9 +1532,9 @@ static auto ImportFunctionDecl(Context& context, SemIR::LocId loc_id,
if (clang::FunctionDecl* thunk_clang_decl =
BuildCppThunk(context, function_info)) {
if (auto thunk_function_id =
ImportFunction(context, loc_id, thunk_clang_decl,
thunk_clang_decl->getNumParams())) {
if (auto thunk_function_id = ImportFunction(
context, loc_id, import_ir_inst_id, thunk_clang_decl,
thunk_clang_decl->getNumParams())) {
SemIR::InstId thunk_function_decl_id =
context.functions().Get(*thunk_function_id).first_owning_decl_id;
function_info.SetHasCppThunk(thunk_function_decl_id);