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Perform overload resolution immediately in C++ operator lookup. (#6416)

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Don't attempt to defer overload resolution by creating a
`CppOverloadSet`; this was incorrect as we weren't saving the complete
clang::OverloadCandidateSet, resulting in template candidates not being
found. Moreover, saving the overload candidate set would be expensive,
as the representation is surprisingly large, and is unnecessary since
we're about to build a call.

In passing, improve the diagnostics for overload resolution failure to
use Clang's operator overload resolution messages rather than its call
overload resolution messages.

This fixes calls to templated operator overloads, which is the final
piece needed for us to successfully compile an iostream-based "Hello
world" program.

---------

Co-authored-by: Jon Ross-Perkins <jperkins@google.com>
This commit is contained in:
Richard Smith
2025-11-24 23:01:28 +00:00
committed by GitHub
co-authored by Jon Ross-Perkins
parent 167b45ca35
commit 054dfca685
8 changed files with 339 additions and 133 deletions
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toolchain/check/cpp/overload_resolution.cpp
+22 -24
View File
@@ -84,22 +84,27 @@ static auto AddOverloadCandidates(clang::Sema& sema,
}
}
// Checks whether a selected overload is accessible and diagnoses if not.
static auto CheckOverloadAccess(Context& context, SemIR::LocId loc_id,
const SemIR::CppOverloadSet& overload_set,
clang::DeclAccessPair overload,
SemIR::InstId overload_inst_id) -> void {
auto CheckCppOverloadAccess(
Context& context, SemIR::LocId loc_id, clang::DeclAccessPair overload,
SemIR::KnownInstId<SemIR::FunctionDecl> overload_inst_id,
SemIR::NameScopeId parent_scope_id) -> void {
SemIR::AccessKind member_access_kind = MapCppAccess(overload);
if (member_access_kind == SemIR::AccessKind::Public) {
return;
}
auto function_id = context.insts().Get(overload_inst_id).function_id;
auto& function = context.functions().Get(function_id);
if (!parent_scope_id.has_value()) {
parent_scope_id = function.parent_scope_id;
}
auto name_scope_const_id = context.constant_values().Get(
context.name_scopes().Get(overload_set.parent_scope_id).inst_id());
context.name_scopes().Get(parent_scope_id).inst_id());
SemIR::AccessKind allowed_access_kind =
GetHighestAllowedAccess(context, loc_id, name_scope_const_id);
CheckAccess(context, loc_id, SemIR::LocId(overload_inst_id),
overload_set.name_id, member_access_kind,
CheckAccess(context, loc_id, SemIR::LocId(overload_inst_id), function.name_id,
member_access_kind,
/*is_parent_access=*/false,
{.constant_id = name_scope_const_id,
.highest_allowed_access = allowed_access_kind});
@@ -155,25 +160,18 @@ auto PerformCppOverloadResolution(Context& context, SemIR::LocId loc_id,
switch (overloading_result) {
case clang::OverloadingResult::OR_Success: {
// TODO: Handle the cases when Function is null.
CARBON_CHECK(best_viable_fn->Function);
if (best_viable_fn->RewriteKind) {
context.TODO(
loc_id,
llvm::formatv("Rewriting operator{0} using {1} is not supported",
clang::getOperatorSpelling(
candidate_set.getRewriteInfo().OriginalOperator),
best_viable_fn->Function->getNameAsString()));
return SemIR::ErrorInst::InstId;
}
CARBON_CHECK(!best_viable_fn->RewriteKind);
sema.MarkFunctionReferenced(loc, best_viable_fn->Function);
SemIR::InstId result_id = ImportCppFunctionDecl(
context, loc_id, best_viable_fn->Function,
// If this is an operator method, the first arg will be used as self.
arg_exprs.size() -
(IsCppOperatorMethodDecl(best_viable_fn->Function) ? 1 : 0));
CheckOverloadAccess(context, loc_id, overload_set,
best_viable_fn->FoundDecl, result_id);
context, loc_id, best_viable_fn->Function, arg_exprs.size());
if (auto fn_decl =
context.insts().TryGetAsWithId<SemIR::FunctionDecl>(result_id)) {
CheckCppOverloadAccess(context, loc_id, best_viable_fn->FoundDecl,
fn_decl->inst_id, overload_set.parent_scope_id);
} else {
CARBON_CHECK(result_id == SemIR::ErrorInst::InstId);
}
return result_id;
}
case clang::OverloadingResult::OR_No_Viable_Function: {