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Handle pack expansion for dependent non-type template params (#6850)

Browse Source 
https://github.com/carbon-language/carbon-lang/issues/6717
This commit is contained in:
Nicholas Bishop
2026-03-09 14:49:31 +00:00
committed by GitHub
parent 0dac40e793
commit cdcd3ab66c
2 changed files with 31 additions and 8 deletions
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toolchain/check/cpp/call.cpp
+17 -8
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@@ -112,7 +112,8 @@ static auto MakePlaceholderTemplateArg(Context& context, SemIR::InstId arg_id)
static auto ConvertArgToTemplateArg(
Context& context, clang::TemplateDecl* template_decl,
clang::NamedDecl* param_decl, SemIR::InstId arg_id,
clang::SmallVector<clang::TemplateArgument>* template_args, bool diagnose)
clang::SmallVector<clang::TemplateArgument>* template_args,
unsigned argument_pack_index, bool diagnose)
-> std::optional<clang::TemplateArgumentLoc> {
if (isa<clang::TemplateTypeParmDecl>(param_decl)) {
auto type = ExprAsType(context, SemIR::LocId(arg_id), arg_id, diagnose);
@@ -153,6 +154,9 @@ static auto ConvertArgToTemplateArg(
if (auto* non_type = dyn_cast<clang::NonTypeTemplateParmDecl>(param_decl)) {
auto param_type = non_type->getType();
if (non_type->isParameterPack() && non_type->isExpandedParameterPack()) {
param_type = non_type->getExpansionType(argument_pack_index);
}
// Handle non-type parameters with a dependent type. For example:
//
@@ -179,9 +183,13 @@ static auto ConvertArgToTemplateArg(
/*Final=*/true);
mltal.addOuterRetainedLevels(non_type->getDepth());
// TODO: handle pack expansion by passing in the pack index from
// `ConvertArgsToTemplateArgs`.
if (!param_type->getAs<clang::PackExpansionType>()) {
if (const auto* pet = param_type->getAs<clang::PackExpansionType>()) {
clang::Sema::ArgPackSubstIndexRAII subst_index(context.clang_sema(),
argument_pack_index);
param_type = context.clang_sema().SubstType(pet->getPattern(), mltal,
non_type->getLocation(),
non_type->getDeclName());
} else {
param_type = context.clang_sema().SubstType(param_type, mltal,
non_type->getLocation(),
non_type->getDeclName());
@@ -292,12 +300,13 @@ auto ConvertArgsToTemplateArgs(Context& context,
llvm::ArrayRef<SemIR::InstId> args_for_param =
param_decl->isTemplateParameterPack() ? std::exchange(arg_ids, {})
: arg_ids.consume_front();
for (auto arg_id : args_for_param) {
if (auto arg =
ConvertArgToTemplateArg(context, template_decl, param_decl,
arg_id, &template_args, diagnose)) {
for (auto [argument_pack_index, arg_id] : llvm::enumerate(args_for_param)) {
if (auto arg = ConvertArgToTemplateArg(context, template_decl, param_decl,
arg_id, &template_args,
argument_pack_index, diagnose)) {
arg_list.addArgument(*arg);
template_args.push_back(arg->getArgument());
argument_pack_index++;
} else {
return false;
}