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Support dependent non-type template parameters (#6791)

Browse Source 
https://github.com/carbon-language/carbon-lang/issues/6717
This commit is contained in:
Nicholas Bishop
2026-02-25 20:50:04 +00:00
committed by GitHub
parent 142596b49c
commit 157de6e370
2 changed files with 93 additions and 15 deletions
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toolchain/check/cpp/call.cpp
+45 -6
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@@ -5,6 +5,7 @@
#include "toolchain/check/cpp/call.h"
#include "clang/Sema/Sema.h"
#include "clang/Sema/Template.h"
#include "toolchain/base/kind_switch.h"
#include "toolchain/check/call.h"
#include "toolchain/check/cpp/import.h"
@@ -75,9 +76,10 @@ static auto MakePlaceholderTemplateArg(Context& context, SemIR::InstId arg_id)
// Converts an argument in a call to a C++ template name into a corresponding
// clang template argument, given the template parameter it will be matched
// against.
static auto ConvertArgToTemplateArg(Context& context,
const clang::NamedDecl* param_decl,
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)
-> std::optional<clang::TemplateArgumentLoc> {
if (isa<clang::TemplateTypeParmDecl>(param_decl)) {
auto type = ExprAsType(context, SemIR::LocId(arg_id), arg_id);
@@ -114,10 +116,44 @@ static auto ConvertArgToTemplateArg(Context& context,
return MakePlaceholderTemplateArg(context, arg_id);
}
if (const auto* non_type =
dyn_cast<clang::NonTypeTemplateParmDecl>(param_decl)) {
if (auto* non_type = dyn_cast<clang::NonTypeTemplateParmDecl>(param_decl)) {
auto param_type = non_type->getType();
// Handle non-type parameters with a dependent type. For example:
//
// C++: template<typename T, T N> struct S{};
// Carbon: Cpp.S(i32, 42)
//
// When evaluating the second template argument, the generic type of
// `T` should be substituted with `i32`.
if (param_type->isInstantiationDependentType()) {
clang::Sema::InstantiatingTemplate inst(
context.clang_sema(), clang::SourceLocation(), param_decl, non_type,
*template_args, clang::SourceRange());
if (inst.isInvalid()) {
return std::nullopt;
}
clang::MultiLevelTemplateArgumentList mltal(template_decl, *template_args,
/*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>()) {
param_type = context.clang_sema().SubstType(param_type, mltal,
non_type->getLocation(),
non_type->getDeclName());
}
if (!param_type.isNull()) {
param_type = context.clang_sema().CheckNonTypeTemplateParameterType(
param_type, non_type->getLocation());
}
if (param_type.isNull()) {
return std::nullopt;
}
}
// Handle integer parameters.
if (param_type->isIntegerType()) {
// Get the Carbon type corresponding to the parameter's Clang type.
@@ -172,6 +208,7 @@ static auto ConvertArgsToTemplateArgs(Context& context,
llvm::ArrayRef<SemIR::InstId> arg_ids,
clang::TemplateArgumentListInfo& arg_list)
-> bool {
clang::SmallVector<clang::TemplateArgument> template_args;
for (auto* param_decl : template_decl->getTemplateParameters()->asArray()) {
if (arg_ids.empty()) {
return true;
@@ -185,8 +222,10 @@ static auto ConvertArgsToTemplateArgs(Context& context,
param_decl->isTemplateParameterPack() ? std::exchange(arg_ids, {})
: arg_ids.consume_front();
for (auto arg_id : args_for_param) {
if (auto arg = ConvertArgToTemplateArg(context, param_decl, arg_id)) {
if (auto arg = ConvertArgToTemplateArg(context, template_decl, param_decl,
arg_id, &template_args)) {
arg_list.addArgument(*arg);
template_args.push_back(arg->getArgument());
} else {
return false;
}