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//===-- CxxModuleHandler.cpp ------------------------------------*- C++ -*-===//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
#include "lldb/Symbol/CxxModuleHandler.h"
#include "lldb/Symbol/ClangASTContext.h"
#include "lldb/Utility/Log.h"
#include "clang/Sema/Lookup.h"
#include "llvm/Support/Error.h"
using namespace lldb_private;
using namespace clang;
CxxModuleHandler::CxxModuleHandler(ASTImporter &importer, ASTContext *target)
: m_importer(&importer),
m_sema(ClangASTContext::GetASTContext(target)->getSema()) {
std::initializer_list<const char *> supported_names = {
// containers
// pointers
// utility
m_supported_templates.insert(supported_names.begin(), supported_names.end());
/// Builds a list of scopes that point into the given context.
/// \param sema The sema that will be using the scopes.
/// \param ctxt The context that the scope should look into.
/// \param result A list of scopes. The scopes need to be freed by the caller
/// (except the TUScope which is owned by the sema).
static void makeScopes(Sema &sema, DeclContext *ctxt,
std::vector<Scope *> &result) {
// FIXME: The result should be a list of unique_ptrs, but the TUScope makes
// this currently impossible as it's owned by the Sema.
if (auto parent = ctxt->getParent()) {
makeScopes(sema, parent, result);
Scope *scope =
new Scope(result.back(), Scope::DeclScope, sema.getDiagnostics());
} else
/// Uses the Sema to look up the given name in the given DeclContext.
static std::unique_ptr<LookupResult>
emulateLookupInCtxt(Sema &sema, llvm::StringRef name, DeclContext *ctxt) {
IdentifierInfo &ident = sema.getASTContext().Idents.get(name);
std::unique_ptr<LookupResult> lookup_result;
lookup_result.reset(new LookupResult(sema, DeclarationName(&ident),
// Usually during parsing we already encountered the scopes we would use. But
// here don't have these scopes so we have to emulate the behavior of the
// Sema during parsing.
std::vector<Scope *> scopes;
makeScopes(sema, ctxt, scopes);
// Now actually perform the lookup with the sema.
sema.LookupName(*lookup_result, scopes.back());
// Delete all the allocated scopes beside the translation unit scope (which
// has depth 0).
for (Scope *s : scopes)
if (s->getDepth() != 0)
delete s;
return lookup_result;
/// Error class for handling problems when finding a certain DeclContext.
struct MissingDeclContext : public llvm::ErrorInfo<MissingDeclContext> {
static char ID;
MissingDeclContext(DeclContext *context, std::string error)
: m_context(context), m_error(error) {}
DeclContext *m_context;
std::string m_error;
void log(llvm::raw_ostream &OS) const override {
OS << llvm::formatv("error when reconstructing context of kind {0}:{1}",
m_context->getDeclKindName(), m_error);
std::error_code convertToErrorCode() const override {
return llvm::inconvertibleErrorCode();
char MissingDeclContext::ID = 0;
/// Given a foreign decl context, this function finds the equivalent local
/// decl context in the ASTContext of the given Sema. Potentially deserializes
/// decls from the 'std' module if necessary.
static llvm::Expected<DeclContext *>
getEqualLocalDeclContext(Sema &sema, DeclContext *foreign_ctxt) {
// Inline namespaces don't matter for lookups, so let's skip them.
while (foreign_ctxt && foreign_ctxt->isInlineNamespace())
foreign_ctxt = foreign_ctxt->getParent();
// If the foreign context is the TU, we just return the local TU.
if (foreign_ctxt->isTranslationUnit())
return sema.getASTContext().getTranslationUnitDecl();
// Recursively find/build the parent DeclContext.
llvm::Expected<DeclContext *> parent =
getEqualLocalDeclContext(sema, foreign_ctxt->getParent());
if (!parent)
return parent;
// We currently only support building namespaces.
if (foreign_ctxt->isNamespace()) {
NamedDecl *ns = llvm::dyn_cast<NamedDecl>(foreign_ctxt);
llvm::StringRef ns_name = ns->getName();
auto lookup_result = emulateLookupInCtxt(sema, ns_name, *parent);
for (NamedDecl *named_decl : *lookup_result) {
if (DeclContext *DC = llvm::dyn_cast<DeclContext>(named_decl))
return DC->getPrimaryContext();
return llvm::make_error<MissingDeclContext>(
"Couldn't find namespace " + ns->getQualifiedNameAsString());
return llvm::make_error<MissingDeclContext>(foreign_ctxt, "Unknown context ");
/// Returns true iff tryInstantiateStdTemplate supports instantiating a template
/// with the given template arguments.
static bool templateArgsAreSupported(ArrayRef<TemplateArgument> a) {
for (const TemplateArgument &arg : a) {
switch (arg.getKind()) {
case TemplateArgument::Type:
case TemplateArgument::Integral:
// TemplateArgument kind hasn't been handled yet.
return false;
return true;
/// Constructor function for Clang declarations. Ensures that the created
/// declaration is registered with the ASTImporter.
template <typename T, typename... Args>
T *createDecl(ASTImporter &importer, Decl *from_d, Args &&... args) {
T *to_d = T::Create(std::forward<Args>(args)...);
importer.RegisterImportedDecl(from_d, to_d);
return to_d;
llvm::Optional<Decl *> CxxModuleHandler::tryInstantiateStdTemplate(Decl *d) {
// If we don't have a template to instiantiate, then there is nothing to do.
auto td = dyn_cast<ClassTemplateSpecializationDecl>(d);
if (!td)
return {};
// We only care about templates in the std namespace.
if (!td->getDeclContext()->isStdNamespace())
return {};
// We have a whitelist of supported template names.
if (m_supported_templates.find(td->getName()) == m_supported_templates.end())
return {};
// Early check if we even support instantiating this template. We do this
// before we import anything into the target AST.
auto &foreign_args = td->getTemplateInstantiationArgs();
if (!templateArgsAreSupported(foreign_args.asArray()))
return {};
// Find the local DeclContext that corresponds to the DeclContext of our
// decl we want to import.
auto to_context = getEqualLocalDeclContext(*m_sema, td->getDeclContext());
if (!to_context)
return {};
// Look up the template in our local context.
std::unique_ptr<LookupResult> lookup =
emulateLookupInCtxt(*m_sema, td->getName(), *to_context);
ClassTemplateDecl *new_class_template = nullptr;
for (auto LD : *lookup) {
if ((new_class_template = dyn_cast<ClassTemplateDecl>(LD)))
if (!new_class_template)
return {};
// Import the foreign template arguments.
llvm::SmallVector<TemplateArgument, 4> imported_args;
Log *log = lldb_private::GetLogIfAllCategoriesSet(LIBLLDB_LOG_EXPRESSIONS);
// If this logic is changed, also update templateArgsAreSupported.
for (const TemplateArgument &arg : foreign_args.asArray()) {
switch (arg.getKind()) {
case TemplateArgument::Type: {
llvm::Expected<QualType> type = m_importer->Import(arg.getAsType());
if (!type) {
LLDB_LOG_ERROR(log, type.takeError(), "Couldn't import type: {0}");
return {};
case TemplateArgument::Integral: {
llvm::APSInt integral = arg.getAsIntegral();
llvm::Expected<QualType> type =
if (!type) {
LLDB_LOG_ERROR(log, type.takeError(), "Couldn't import type: {0}");
return {};
TemplateArgument(d->getASTContext(), integral, *type));
assert(false && "templateArgsAreSupported not updated?");
// Find the class template specialization declaration that
// corresponds to these arguments.
void *InsertPos = nullptr;
ClassTemplateSpecializationDecl *result =
new_class_template->findSpecialization(imported_args, InsertPos);
if (result) {
// We found an existing specialization in the module that fits our arguments
// so we can treat it as the result and register it with the ASTImporter.
m_importer->RegisterImportedDecl(d, result);
return result;
// Instantiate the template.
result = createDecl<ClassTemplateSpecializationDecl>(
*m_importer, d, m_sema->getASTContext(),
new_class_template->getLocation(), new_class_template, imported_args,
new_class_template->AddSpecialization(result, InsertPos);
if (new_class_template->isOutOfLine())
return result;
llvm::Optional<Decl *> CxxModuleHandler::Import(Decl *d) {
if (!isValid())
return {};
return tryInstantiateStdTemplate(d);