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Reverse Interop: Nested namespace support (#6940)

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Start recording the clang::DeclContext* -> InstId mapping for use in
later operations.

The test update includes removing the initial fail_* test because I
hadn't thought about the use of namespace aliases as a way to test for
the presence of a namespace without the failure caused by not finding
the thing inside the namespace.

---------

Co-authored-by: Jon Ross-Perkins <jperkins@google.com>
This commit is contained in:
David Blaikie
2026-03-24 19:55:25 +00:00
committed by GitHub
co-authored by Jon Ross-Perkins
parent f9e1806c4a
commit 2af5f971da
2 changed files with 59 additions and 35 deletions
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toolchain/check/cpp/generate_ast.cpp
+55 -20
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@@ -20,6 +20,7 @@
#include "clang/Sema/MultiplexExternalSemaSource.h"
#include "clang/Sema/Sema.h"
#include "common/check.h"
#include "common/map.h"
#include "common/raw_string_ostream.h"
#include "llvm/ADT/IntrusiveRefCntPtr.h"
#include "llvm/ADT/StringRef.h"
@@ -306,22 +307,41 @@ class ShallowCopyCompilerInvocation : public clang::CompilerInvocation {
}
};
// Provides clang AST nodes representing Carbon SemIR entities.
class CarbonExternalASTSource : public clang::ExternalASTSource {
public:
explicit CarbonExternalASTSource(Context* context,
clang::ASTContext* ast_context)
: context_(context), ast_context_(ast_context) {}
// Look up decls for `decl_name` inside `decl_context`, adding the decls to
// `decl_context`. Returns true if any decls were added.
auto FindExternalVisibleDeclsByName(
const clang::DeclContext* decl_context, clang::DeclarationName decl_name,
const clang::DeclContext* original_decl_context) -> bool override;
// See clang::ExternalASTSource.
auto StartTranslationUnit(clang::ASTConsumer* consumer) -> void override;
private:
// Map a Carbon entity to a Clang NamedDecl. Returns null if the entity cannot
// currently be represented in C++.
auto MapInstIdToClangDecl(clang::DeclContext& decl_context,
LookupResult lookup) -> clang::NamedDecl*;
Check::Context* context_;
clang::ASTContext* ast_context_;
clang::NamespaceDecl* carbon_cpp_namespace_ = nullptr;
// The association between clang DeclContexts and the corresponding
// SemIR::Namespaces in Carbon.
// TODO: reuse the SemIR::File::ClangDeclStore to avoid duplicates, and to
// enable roundtripping through forward and reverse interop (once we have
// syntax/support for that).
Map<clang::DeclContext*, SemIR::InstId> scope_map_;
// Has the "Carbon" C++ namespace been created yet
// (this could be replaced with `!scope_map_.empty()` if Carbon::Map supported
// `empty()`)
bool root_scope_initialized_ = false;
};
void CarbonExternalASTSource::StartTranslationUnit(
@@ -332,25 +352,28 @@ void CarbonExternalASTSource::StartTranslationUnit(
translation_unit.setHasExternalVisibleStorage();
}
// Map a Carbon entity to a Clang NamedDecl.
static auto MapInstIdToClangDecl(Context& context,
clang::ASTContext& ast_context,
clang::DeclContext& decl_context,
LookupResult lookup) -> clang::NamedDecl* {
auto CarbonExternalASTSource::MapInstIdToClangDecl(
clang::DeclContext& decl_context, LookupResult lookup)
-> clang::NamedDecl* {
auto target_inst_id = lookup.scope_result.target_inst_id();
if (auto target_inst =
context.insts().TryGetAs<SemIR::Namespace>(target_inst_id)) {
auto& name_scope = context.name_scopes().Get(target_inst->name_scope_id);
context_->insts().TryGetAs<SemIR::Namespace>(target_inst_id)) {
auto& name_scope = context_->name_scopes().Get(target_inst->name_scope_id);
auto* identifier_info =
GetClangIdentifierInfo(context, name_scope.name_id());
GetClangIdentifierInfo(*context_, name_scope.name_id());
// TODO: Don't immediately use the decl_context - build any intermediate
// namespaces iteratively.
// Eventually add a mapping and use that/populate it/keep it up to date.
// decl_context could be prepopulated in that mapping and not passed
// explicitly to MapInstIdToClangDecl.
return clang::NamespaceDecl::Create(
ast_context, &decl_context, false, clang::SourceLocation(),
auto* namespace_decl = clang::NamespaceDecl::Create(
*ast_context_, &decl_context, false, clang::SourceLocation(),
clang::SourceLocation(), identifier_info, nullptr, false);
auto result =
scope_map_.Insert(namespace_decl->getPrimaryContext(), target_inst_id);
CARBON_CHECK(result.is_inserted(), "Inserting over an existing entry.");
namespace_decl->setHasExternalVisibleStorage();
return namespace_decl;
}
return nullptr;
}
@@ -358,8 +381,12 @@ static auto MapInstIdToClangDecl(Context& context,
auto CarbonExternalASTSource::FindExternalVisibleDeclsByName(
const clang::DeclContext* decl_context, clang::DeclarationName decl_name,
const clang::DeclContext* /*OriginalDC*/) -> bool {
if (decl_context != carbon_cpp_namespace_) {
if (decl_context->getDeclKind() != clang::Decl::Kind::TranslationUnit) {
if (decl_context->getDeclKind() == clang::Decl::Kind::TranslationUnit) {
// If the context doesn't already have a mapping between C++ and Carbon,
// check if this is the root mapping (for the "Carbon" namespace in the
// translation unit scope) and if so, create that mapping.
if (root_scope_initialized_) {
return false;
}
@@ -372,17 +399,25 @@ auto CarbonExternalASTSource::FindExternalVisibleDeclsByName(
// Build the top level 'Carbon' namespace
auto& ast_context = decl_context->getParentASTContext();
auto& mutable_tu_decl_context = *ast_context.getTranslationUnitDecl();
carbon_cpp_namespace_ = clang::NamespaceDecl::Create(
auto* carbon_cpp_namespace = clang::NamespaceDecl::Create(
ast_context, &mutable_tu_decl_context, false, clang::SourceLocation(),
clang::SourceLocation(), &ast_context.Idents.get(carbon_namespace_name),
nullptr, false);
carbon_cpp_namespace_->setHasExternalVisibleStorage();
carbon_cpp_namespace->setHasExternalVisibleStorage();
auto result = scope_map_.Insert(carbon_cpp_namespace->getPrimaryContext(),
SemIR::Namespace::PackageInstId);
CARBON_CHECK(result.is_inserted(), "Inserting over an existing entry.");
SetExternalVisibleDeclsForName(decl_context, decl_name,
{carbon_cpp_namespace_});
{carbon_cpp_namespace});
root_scope_initialized_ = true;
return true;
}
// Lookup the name in Carbon package scope
auto decl_context_inst_id =
scope_map_.Lookup(decl_context->getPrimaryContext());
CARBON_CHECK(
decl_context_inst_id,
"The DeclContext should already be associated with a Carbon InstId.");
llvm::SmallVector<Check::LookupScope> lookup_scopes;
@@ -390,7 +425,7 @@ auto CarbonExternalASTSource::FindExternalVisibleDeclsByName(
// here - completeness should've been checked by clang before this point.
if (!AppendLookupScopesForConstant(
*context_, SemIR::LocId::None,
context_->constant_values().Get(SemIR::Namespace::PackageInstId),
context_->constant_values().Get(decl_context_inst_id.value()),
SemIR::ConstantId::None, &lookup_scopes)) {
return false;
}
@@ -413,8 +448,8 @@ auto CarbonExternalASTSource::FindExternalVisibleDeclsByName(
}
// Map the found Carbon entity to a Clang NamedDecl.
auto* clang_decl = MapInstIdToClangDecl(*context_, *ast_context_,
*carbon_cpp_namespace_, result);
// Use the key to reach the owned, mutable copy of decl_context.
auto* clang_decl = MapInstIdToClangDecl(*decl_context_inst_id.key(), result);
if (!clang_decl) {
return false;
}