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carbon-lang/toolchain/check/cpp/generate_ast.cpp
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Richard SmithandDavid Blaikie d5ec82e7ac Don't crash if clang setup fails. (#6804) 
Defer creating the CppContext until we have all of its components, so
that we know they're not null. Don't track the action on the context,
since it's not a reliable way of getting back to the compiler invocation
on failure. Don't flush the diagnostics emitter from the emitter
destructor since the derived class emitter will already have been
destroyed at that point. Distinguish between clang setup failing and
clang merely producing errors, and don't connect the check context to
clang if clang setup failed.

---------

Co-authored-by: David Blaikie <dblaikie@gmail.com>
2026-02-27 02:44:08 +00:00

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// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
// Exceptions. See /LICENSE for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
#include "toolchain/check/cpp/generate_ast.h"
#include <memory>
#include <string>
#include "clang/AST/ASTContext.h"
#include "clang/Basic/FileManager.h"
#include "clang/CodeGen/ModuleBuilder.h"
#include "clang/Frontend/CompilerInstance.h"
#include "clang/Frontend/CompilerInvocation.h"
#include "clang/Frontend/FrontendAction.h"
#include "clang/Frontend/TextDiagnostic.h"
#include "clang/Lex/PreprocessorOptions.h"
#include "clang/Parse/Parser.h"
#include "clang/Sema/ExternalSemaSource.h"
#include "clang/Sema/Sema.h"
#include "common/check.h"
#include "common/raw_string_ostream.h"
#include "llvm/ADT/IntrusiveRefCntPtr.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/Support/raw_ostream.h"
#include "toolchain/check/context.h"
#include "toolchain/diagnostics/diagnostic.h"
#include "toolchain/diagnostics/emitter.h"
#include "toolchain/diagnostics/format_providers.h"
#include "toolchain/parse/node_ids.h"
#include "toolchain/sem_ir/cpp_file.h"
namespace Carbon::Check {
// Add a line marker directive pointing at the location of the `import Cpp`
// declaration in the Carbon source file. This will cause Clang's diagnostics
// machinery to track and report the location in Carbon code where the import
// was written.
static auto GenerateLineMarker(Context& context, llvm::raw_ostream& out,
int line) {
out << "# " << line << " \""
<< FormatEscaped(context.tokens().source().filename()) << "\"\n";
}
// Generates C++ file contents to #include all requested imports.
static auto GenerateCppIncludesHeaderCode(
Context& context, llvm::ArrayRef<Parse::Tree::PackagingNames> imports)
-> std::string {
std::string code;
llvm::raw_string_ostream code_stream(code);
for (const Parse::Tree::PackagingNames& import : imports) {
if (import.inline_body_id.has_value()) {
// Expand `import Cpp inline "code";` directly into the specified code.
auto code_token = context.parse_tree().node_token(import.inline_body_id);
// Compute the line number on which the C++ code starts. Usually the code
// is specified as a block string literal and starts on the line after the
// start of the string token.
// TODO: Determine if this is a block string literal without calling
// `GetTokenText`, which re-lexes the string.
int line = context.tokens().GetLineNumber(code_token);
if (context.tokens().GetTokenText(code_token).contains('\n')) {
++line;
}
GenerateLineMarker(context, code_stream, line);
code_stream << context.string_literal_values().Get(
context.tokens().GetStringLiteralValue(code_token))
<< "\n";
// TODO: Inject a clang pragma here to produce an error if there are
// unclosed scopes at the end of this inline C++ fragment.
} else if (import.library_id.has_value()) {
// Translate `import Cpp library "foo.h";` into `#include "foo.h"`.
GenerateLineMarker(context, code_stream,
context.tokens().GetLineNumber(
context.parse_tree().node_token(import.node_id)));
auto name = context.string_literal_values().Get(import.library_id);
if (name.starts_with('<') && name.ends_with('>')) {
code_stream << "#include <"
<< FormatEscaped(name.drop_front().drop_back()) << ">\n";
} else {
code_stream << "#include \"" << FormatEscaped(name) << "\"\n";
}
}
}
// Inject a declaration of placement operator new, because the code we
// generate in thunks depends on it for placement new expressions. Clang has
// special-case logic for lowering a new-expression using this, so a
// definition is not required.
// TODO: This is a hack. We should be able to directly generate Clang AST to
// construct objects in-place without this.
// TODO: Once we can rely on libc++ being available, consider including
// `<__new/placement_new_delete.h>` instead.
code_stream << R"(# 1 "<carbon-internal>"
#undef constexpr
#if __cplusplus > 202302L
constexpr
#endif
#undef void
#undef operator
#undef new
void* operator new(__SIZE_TYPE__, void*)
#if __cplusplus < 201103L
#undef throw
throw()
#else
#undef noexcept
noexcept
#endif
;
)";
return code;
}
// Adds the given source location and an `ImportIRInst` referring to it in
// `ImportIRId::Cpp`.
static auto AddImportIRInst(SemIR::File& file,
clang::SourceLocation clang_source_loc)
-> SemIR::ImportIRInstId {
SemIR::ClangSourceLocId clang_source_loc_id =
file.clang_source_locs().Add(clang_source_loc);
return file.import_ir_insts().Add(SemIR::ImportIRInst(clang_source_loc_id));
}
namespace {
// Used to convert Clang diagnostics to Carbon diagnostics.
//
// Handling of Clang notes is a little subtle: as far as Clang is concerned,
// notes are separate diagnostics, not connected to the error or warning that
// precedes them. But in Carbon's diagnostics system, notes are part of the
// enclosing diagnostic. To handle this, we buffer Clang diagnostics until we
// reach a point where we know we're not in the middle of a diagnostic, and then
// emit a diagnostic along with all of its notes. This is triggered when adding
// or removing a Carbon context note, which could otherwise get attached to the
// wrong C++ diagnostics, and at the end of the Carbon program.
class CarbonClangDiagnosticConsumer : public clang::DiagnosticConsumer {
public:
// Creates an instance with the location that triggers calling Clang. The
// `context` is not stored here, and the diagnostics consumer is expected to
// outlive it.
explicit CarbonClangDiagnosticConsumer(
Context& context, std::shared_ptr<clang::CompilerInvocation> invocation)
: sem_ir_(&context.sem_ir()),
emitter_(&context.emitter()),
invocation_(std::move(invocation)) {
emitter_->AddFlushFn([this] { EmitDiagnostics(); });
}
~CarbonClangDiagnosticConsumer() override {
// Do not inspect `emitter_` here; it's typically destroyed before the
// consumer is.
// TODO: If Clang produces diagnostics after check finishes, they'll get
// added to the list of pending diagnostics and never emitted.
CARBON_CHECK(diagnostic_infos_.empty(),
"Missing flush before destroying diagnostic consumer");
}
// Generates a Carbon warning for each Clang warning and a Carbon error for
// each Clang error or fatal.
auto HandleDiagnostic(clang::DiagnosticsEngine::Level diag_level,
const clang::Diagnostic& info) -> void override {
DiagnosticConsumer::HandleDiagnostic(diag_level, info);
SemIR::ImportIRInstId clang_import_ir_inst_id =
AddImportIRInst(*sem_ir_, info.getLocation());
llvm::SmallString<256> message;
info.FormatDiagnostic(message);
// Render a code snippet including any highlighted ranges and fixit hints.
// TODO: Also include the #include stack and macro expansion stack in the
// diagnostic output in some way.
RawStringOstream snippet_stream;
if (!info.hasSourceManager()) {
// If we don't have a source manager, this is an error from early in the
// frontend. Don't produce a snippet.
CARBON_CHECK(info.getLocation().isInvalid());
} else {
CodeContextRenderer(snippet_stream, invocation_->getLangOpts(),
invocation_->getDiagnosticOpts())
.emitDiagnostic(
clang::FullSourceLoc(info.getLocation(), info.getSourceManager()),
diag_level, message, info.getRanges(), info.getFixItHints());
}
diagnostic_infos_.push_back({.level = diag_level,
.import_ir_inst_id = clang_import_ir_inst_id,
.message = message.str().str(),
.snippet = snippet_stream.TakeStr()});
}
// Returns the diagnostic to use for a given Clang diagnostic level.
static auto GetDiagnostic(clang::DiagnosticsEngine::Level level)
-> const Diagnostics::DiagnosticBase<std::string>& {
switch (level) {
case clang::DiagnosticsEngine::Ignored: {
CARBON_FATAL("Emitting an ignored diagnostic");
break;
}
case clang::DiagnosticsEngine::Note: {
CARBON_DIAGNOSTIC(CppInteropParseNote, Note, "{0}", std::string);
return CppInteropParseNote;
}
case clang::DiagnosticsEngine::Remark:
case clang::DiagnosticsEngine::Warning: {
// TODO: Add a distinct Remark level to Carbon diagnostics, and stop
// mapping remarks to warnings.
CARBON_DIAGNOSTIC(CppInteropParseWarning, Warning, "{0}", std::string);
return CppInteropParseWarning;
}
case clang::DiagnosticsEngine::Error:
case clang::DiagnosticsEngine::Fatal: {
CARBON_DIAGNOSTIC(CppInteropParseError, Error, "{0}", std::string);
return CppInteropParseError;
}
}
}
// Outputs Carbon diagnostics based on the collected Clang diagnostics. Must
// be called after the AST is set in the context.
auto EmitDiagnostics() -> void {
CARBON_CHECK(
sem_ir_->cpp_file(),
"Attempted to emit C++ diagnostics before the C++ file is set");
for (size_t i = 0; i != diagnostic_infos_.size(); ++i) {
const ClangDiagnosticInfo& info = diagnostic_infos_[i];
auto builder = emitter_->Build(SemIR::LocId(info.import_ir_inst_id),
GetDiagnostic(info.level), info.message);
builder.OverrideSnippet(info.snippet);
for (; i + 1 < diagnostic_infos_.size() &&
diagnostic_infos_[i + 1].level == clang::DiagnosticsEngine::Note;
++i) {
const ClangDiagnosticInfo& note_info = diagnostic_infos_[i + 1];
builder
.Note(SemIR::LocId(note_info.import_ir_inst_id),
GetDiagnostic(note_info.level), note_info.message)
.OverrideSnippet(note_info.snippet);
}
// TODO: This will apply all current Carbon annotation functions. We
// should instead track how Clang's context notes and Carbon's annotation
// functions are interleaved, and interleave the notes in the same order.
builder.Emit();
}
diagnostic_infos_.clear();
}
private:
// A diagnostics renderer based on clang's TextDiagnostic that captures just
// the code context (the snippet).
class CodeContextRenderer : public clang::TextDiagnostic {
protected:
using TextDiagnostic::TextDiagnostic;
void emitDiagnosticMessage(
clang::FullSourceLoc /*loc*/, clang::PresumedLoc /*ploc*/,
clang::DiagnosticsEngine::Level /*level*/, llvm::StringRef /*message*/,
llvm::ArrayRef<clang::CharSourceRange> /*ranges*/,
clang::DiagOrStoredDiag /*info*/) override {}
void emitDiagnosticLoc(
clang::FullSourceLoc /*loc*/, clang::PresumedLoc /*ploc*/,
clang::DiagnosticsEngine::Level /*level*/,
llvm::ArrayRef<clang::CharSourceRange> /*ranges*/) override {}
// emitCodeContext is inherited from clang::TextDiagnostic.
void emitIncludeLocation(clang::FullSourceLoc /*loc*/,
clang::PresumedLoc /*ploc*/) override {}
void emitImportLocation(clang::FullSourceLoc /*loc*/,
clang::PresumedLoc /*ploc*/,
llvm::StringRef /*module_name*/) override {}
void emitBuildingModuleLocation(clang::FullSourceLoc /*loc*/,
clang::PresumedLoc /*ploc*/,
llvm::StringRef /*module_name*/) override {}
// beginDiagnostic and endDiagnostic are inherited from
// clang::TextDiagnostic in case it wants to do any setup / teardown work.
};
// Information on a Clang diagnostic that can be converted to a Carbon
// diagnostic.
struct ClangDiagnosticInfo {
// The Clang diagnostic level.
clang::DiagnosticsEngine::Level level;
// The ID of the ImportIR instruction referring to the Clang source
// location.
SemIR::ImportIRInstId import_ir_inst_id;
// The Clang diagnostic textual message.
std::string message;
// The code snippet produced by clang.
std::string snippet;
};
// The Carbon file that this C++ compilation is attached to.
SemIR::File* sem_ir_;
// The diagnostic emitter that we're emitting diagnostics into.
DiagnosticEmitterBase* emitter_;
// The compiler invocation that is producing the diagnostics.
std::shared_ptr<clang::CompilerInvocation> invocation_;
// Collects the information for all Clang diagnostics to be converted to
// Carbon diagnostics after the context has been initialized with the Clang
// AST.
llvm::SmallVector<ClangDiagnosticInfo> diagnostic_infos_;
};
// A wrapper around a clang::CompilerInvocation that allows us to make a shallow
// copy of most of the invocation and only make a deep copy of the parts that we
// want to change.
//
// clang::CowCompilerInvocation almost allows this, but doesn't derive from
// CompilerInvocation or support shallow copies from a CompilerInvocation, so is
// not useful to us as we can't build an ASTUnit from it.
class ShallowCopyCompilerInvocation : public clang::CompilerInvocation {
public:
explicit ShallowCopyCompilerInvocation(
const clang::CompilerInvocation& invocation) {
shallow_copy_assign(invocation);
// Make a deep copy of options that we modify.
FrontendOpts = std::make_shared<clang::FrontendOptions>(*FrontendOpts);
PPOpts = std::make_shared<clang::PreprocessorOptions>(*PPOpts);
}
};
// An action and a set of registered Clang callbacks used to generate an AST
// from a set of Cpp imports.
class GenerateASTAction : public clang::ASTFrontendAction {
public:
explicit GenerateASTAction(Context& context) : context_(&context) {}
protected:
auto CreateASTConsumer(clang::CompilerInstance& clang_instance,
llvm::StringRef /*file*/)
-> std::unique_ptr<clang::ASTConsumer> override {
auto& cpp_file = *context_->sem_ir().cpp_file();
if (!cpp_file.llvm_context()) {
return std::make_unique<clang::ASTConsumer>();
}
auto code_generator =
std::unique_ptr<clang::CodeGenerator>(clang::CreateLLVMCodeGen(
cpp_file.diagnostics(), context_->sem_ir().filename(),
clang_instance.getVirtualFileSystemPtr(),
clang_instance.getHeaderSearchOpts(),
clang_instance.getPreprocessorOpts(),
clang_instance.getCodeGenOpts(), *cpp_file.llvm_context()));
cpp_file.SetCodeGenerator(code_generator.get());
return code_generator;
}
auto BeginSourceFileAction(clang::CompilerInstance& /*clang_instance*/)
-> bool override {
// TODO: Consider creating an `ExternalSemaSource` here and attaching it to
// the compilation.
// TODO: `clang.getPreprocessor().enableIncrementalProcessing();` to avoid
// the TU scope getting torn down before we're done parsing macros.
return true;
}
// Parse the imports and inline C++ fragments. This is notionally very similar
// to `clang::ParseAST`, which `ASTFrontendAction::ExecuteAction` calls, but
// this version doesn't parse C++20 modules and stops just before reaching the
// end of the translation unit.
auto ExecuteAction() -> void override {
clang::CompilerInstance& clang_instance = getCompilerInstance();
clang_instance.createSema(getTranslationUnitKind(),
/*CompletionConsumer=*/nullptr);
auto parser_ptr = std::make_unique<clang::Parser>(
clang_instance.getPreprocessor(), clang_instance.getSema(),
/*SkipFunctionBodies=*/false);
auto& parser = *parser_ptr;
clang_instance.getPreprocessor().EnterMainSourceFile();
if (auto* source = clang_instance.getASTContext().getExternalSource()) {
source->StartTranslationUnit(&clang_instance.getASTConsumer());
}
parser.Initialize();
clang_instance.getSema().ActOnStartOfTranslationUnit();
context_->set_cpp_context(
std::make_unique<CppContext>(clang_instance, std::move(parser_ptr)));
// Don't allow C++20 module declarations in inline Cpp code fragments.
auto module_import_state = clang::Sema::ModuleImportState::NotACXX20Module;
// Parse top-level declarations until we see EOF. Do not parse EOF, as that
// will cause the parser to end the translation unit prematurely.
while (parser.getCurToken().isNot(clang::tok::eof)) {
clang::Parser::DeclGroupPtrTy decl_group;
bool eof = parser.ParseTopLevelDecl(decl_group, module_import_state);
CARBON_CHECK(!eof);
if (decl_group && !clang_instance.getASTConsumer().HandleTopLevelDecl(
decl_group.get())) {
break;
}
}
}
private:
Context* context_;
};
} // namespace
auto GenerateAst(Context& context,
llvm::ArrayRef<Parse::Tree::PackagingNames> imports,
llvm::IntrusiveRefCntPtr<llvm::vfs::FileSystem> fs,
llvm::LLVMContext* llvm_context,
std::shared_ptr<clang::CompilerInvocation> base_invocation)
-> bool {
CARBON_CHECK(!context.cpp_context());
CARBON_CHECK(!context.sem_ir().cpp_file());
auto invocation =
std::make_shared<ShallowCopyCompilerInvocation>(*base_invocation);
// Ask Clang to not leak memory.
invocation->getFrontendOpts().DisableFree = false;
// Build a diagnostics engine.
llvm::IntrusiveRefCntPtr<clang::DiagnosticsEngine> diags(
clang::CompilerInstance::createDiagnostics(
*fs, invocation->getDiagnosticOpts(),
new CarbonClangDiagnosticConsumer(context, invocation),
/*ShouldOwnClient=*/true));
// Extract the input from the frontend invocation and make sure it makes
// sense.
const auto& inputs = invocation->getFrontendOpts().Inputs;
CARBON_CHECK(inputs.size() == 1 &&
inputs[0].getKind().getLanguage() == clang::Language::CXX &&
inputs[0].getKind().getFormat() == clang::InputKind::Source);
llvm::StringRef file_name = inputs[0].getFile();
// Remap the imports file name to the corresponding `#include`s.
// TODO: Modify the frontend options to specify this memory buffer as input
// instead of remapping the file.
std::string includes = GenerateCppIncludesHeaderCode(context, imports);
auto includes_buffer =
llvm::MemoryBuffer::getMemBufferCopy(includes, file_name);
invocation->getPreprocessorOpts().addRemappedFile(file_name,
includes_buffer.release());
auto clang_instance_ptr =
std::make_unique<clang::CompilerInstance>(invocation);
auto& clang_instance = *clang_instance_ptr;
context.sem_ir().set_cpp_file(std::make_unique<SemIR::CppFile>(
std::move(clang_instance_ptr), llvm_context));
clang_instance.setDiagnostics(diags);
clang_instance.setVirtualFileSystem(fs);
clang_instance.createFileManager();
clang_instance.createSourceManager();
if (!clang_instance.createTarget()) {
return false;
}
GenerateASTAction action(context);
if (!action.BeginSourceFile(clang_instance, inputs[0])) {
return false;
}
if (llvm::Error error = action.Execute()) {
// `Execute` currently never fails, but its contract allows it to.
context.TODO(SemIR::LocId::None, "failed to execute clang action: " +
llvm::toString(std::move(error)));
return false;
}
// Flush any diagnostics. We know we're not part-way through emitting a
// diagnostic now.
context.emitter().Flush();
return true;
}
auto FinishAst(Context& context) -> void {
if (!context.cpp_context()) {
return;
}
context.cpp_context()->sema().ActOnEndOfTranslationUnit();
// We don't call FrontendAction::EndSourceFile, because that destroys the AST.
context.set_cpp_context(nullptr);
context.emitter().Flush();
}
} // namespace Carbon::Check
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