blob: 79165e392df6819159e7d5acbc21b420cf2dec01 [file] [log] [blame]
//===--- Preamble.cpp - Reusing expensive parts of the AST ----------------===//
// 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 "Preamble.h"
#include "Compiler.h"
#include "Config.h"
#include "Headers.h"
#include "SourceCode.h"
#include "support/Logger.h"
#include "support/ThreadsafeFS.h"
#include "support/Trace.h"
#include "clang/AST/DeclTemplate.h"
#include "clang/Basic/Diagnostic.h"
#include "clang/Basic/DiagnosticLex.h"
#include "clang/Basic/LangOptions.h"
#include "clang/Basic/SourceLocation.h"
#include "clang/Basic/SourceManager.h"
#include "clang/Basic/TokenKinds.h"
#include "clang/Frontend/CompilerInvocation.h"
#include "clang/Frontend/FrontendActions.h"
#include "clang/Lex/HeaderSearch.h"
#include "clang/Lex/Lexer.h"
#include "clang/Lex/PPCallbacks.h"
#include "clang/Lex/Preprocessor.h"
#include "clang/Lex/PreprocessorOptions.h"
#include "clang/Tooling/CompilationDatabase.h"
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/DenseSet.h"
#include "llvm/ADT/IntrusiveRefCntPtr.h"
#include "llvm/ADT/None.h"
#include "llvm/ADT/Optional.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SmallString.h"
#include "llvm/ADT/StringExtras.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/ADT/StringSet.h"
#include "llvm/Support/Error.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/FormatVariadic.h"
#include "llvm/Support/MemoryBuffer.h"
#include "llvm/Support/Path.h"
#include "llvm/Support/VirtualFileSystem.h"
#include "llvm/Support/raw_ostream.h"
#include <iterator>
#include <memory>
#include <string>
#include <system_error>
#include <utility>
#include <vector>
namespace clang {
namespace clangd {
namespace {
constexpr llvm::StringLiteral PreamblePatchHeaderName = "__preamble_patch__.h";
bool compileCommandsAreEqual(const tooling::CompileCommand &LHS,
const tooling::CompileCommand &RHS) {
// We don't check for Output, it should not matter to clangd.
return LHS.Directory == RHS.Directory && LHS.Filename == RHS.Filename &&
class CppFilePreambleCallbacks : public PreambleCallbacks {
CppFilePreambleCallbacks(PathRef File, PreambleParsedCallback ParsedCallback)
: File(File), ParsedCallback(ParsedCallback) {}
IncludeStructure takeIncludes() { return std::move(Includes); }
MainFileMacros takeMacros() { return std::move(Macros); }
std::vector<PragmaMark> takeMarks() { return std::move(Marks); }
CanonicalIncludes takeCanonicalIncludes() { return std::move(CanonIncludes); }
bool isMainFileIncludeGuarded() const { return IsMainFileIncludeGuarded; }
void AfterExecute(CompilerInstance &CI) override {
if (ParsedCallback) {
trace::Span Tracer("Running PreambleCallback");
ParsedCallback(CI.getASTContext(), CI.getPreprocessorPtr(),
const SourceManager &SM = CI.getSourceManager();
const FileEntry *MainFE = SM.getFileEntryForID(SM.getMainFileID());
IsMainFileIncludeGuarded =
void BeforeExecute(CompilerInstance &CI) override {
LangOpts = &CI.getLangOpts();
SourceMgr = &CI.getSourceManager();
Compiler = &CI;
std::unique_ptr<PPCallbacks> createPPCallbacks() override {
assert(SourceMgr && LangOpts &&
"SourceMgr and LangOpts must be set at this point");
return std::make_unique<PPChainedCallbacks>(
std::make_unique<CollectMainFileMacros>(*SourceMgr, Macros),
collectPragmaMarksCallback(*SourceMgr, Marks)));
CommentHandler *getCommentHandler() override {
IWYUHandler = collectIWYUHeaderMaps(&CanonIncludes);
return IWYUHandler.get();
bool shouldSkipFunctionBody(Decl *D) override {
// Generally we skip function bodies in preambles for speed.
// We can make exceptions for functions that are cheap to parse and
// instantiate, widely used, and valuable (e.g. commonly produce errors).
if (const auto *FT = llvm::dyn_cast<clang::FunctionTemplateDecl>(D)) {
if (const auto *II = FT->getDeclName().getAsIdentifierInfo())
// std::make_unique is trivial, and we diagnose bad constructor calls.
if (II->isStr("make_unique") && FT->isInStdNamespace())
return false;
return true;
PathRef File;
PreambleParsedCallback ParsedCallback;
IncludeStructure Includes;
CanonicalIncludes CanonIncludes;
MainFileMacros Macros;
std::vector<PragmaMark> Marks;
bool IsMainFileIncludeGuarded = false;
std::unique_ptr<CommentHandler> IWYUHandler = nullptr;
const clang::LangOptions *LangOpts = nullptr;
const SourceManager *SourceMgr = nullptr;
const CompilerInstance *Compiler = nullptr;
// Represents directives other than includes, where basic textual information is
// enough.
struct TextualPPDirective {
unsigned DirectiveLine;
// Full text that's representing the directive, including the `#`.
std::string Text;
unsigned Offset;
bool operator==(const TextualPPDirective &RHS) const {
return std::tie(DirectiveLine, Offset, Text) ==
std::tie(RHS.DirectiveLine, RHS.Offset, RHS.Text);
// Formats a PP directive consisting of Prefix (e.g. "#define ") and Body ("X
// 10"). The formatting is copied so that the tokens in Body have PresumedLocs
// with correct columns and lines.
std::string spellDirective(llvm::StringRef Prefix,
CharSourceRange DirectiveRange,
const LangOptions &LangOpts, const SourceManager &SM,
unsigned &DirectiveLine, unsigned &Offset) {
std::string SpelledDirective;
llvm::raw_string_ostream OS(SpelledDirective);
OS << Prefix;
// Make sure DirectiveRange is a char range and doesn't contain macro ids.
DirectiveRange = SM.getExpansionRange(DirectiveRange);
if (DirectiveRange.isTokenRange()) {
Lexer::getLocForEndOfToken(DirectiveRange.getEnd(), 0, SM, LangOpts));
auto DecompLoc = SM.getDecomposedLoc(DirectiveRange.getBegin());
DirectiveLine = SM.getLineNumber(DecompLoc.first, DecompLoc.second);
Offset = DecompLoc.second;
auto TargetColumn = SM.getColumnNumber(DecompLoc.first, DecompLoc.second) - 1;
// Pad with spaces before DirectiveRange to make sure it will be on right
// column when patched.
if (Prefix.size() <= TargetColumn) {
// There is enough space for Prefix and space before directive, use it.
// We try to squeeze the Prefix into the same line whenever we can, as
// putting onto a separate line won't work at the beginning of the file.
OS << std::string(TargetColumn - Prefix.size(), ' ');
} else {
// Prefix was longer than the space we had. We produce e.g.:
// #line N-1
// #define \
// X 10
OS << "\\\n" << std::string(TargetColumn, ' ');
// Decrement because we put an additional line break before
// DirectiveRange.begin().
OS << toSourceCode(SM, DirectiveRange.getAsRange());
return OS.str();
// Collects #define directives inside the main file.
struct DirectiveCollector : public PPCallbacks {
DirectiveCollector(const Preprocessor &PP,
std::vector<TextualPPDirective> &TextualDirectives)
: LangOpts(PP.getLangOpts()), SM(PP.getSourceManager()),
TextualDirectives(TextualDirectives) {}
void FileChanged(SourceLocation Loc, FileChangeReason Reason,
SrcMgr::CharacteristicKind FileType,
FileID PrevFID) override {
InMainFile = SM.isWrittenInMainFile(Loc);
void MacroDefined(const Token &MacroNameTok,
const MacroDirective *MD) override {
if (!InMainFile)
TextualPPDirective &TD = TextualDirectives.back();
const auto *MI = MD->getMacroInfo();
TD.Text =
spellDirective("#define ",
MI->getDefinitionLoc(), MI->getDefinitionEndLoc()),
LangOpts, SM, TD.DirectiveLine, TD.Offset);
bool InMainFile = true;
const LangOptions &LangOpts;
const SourceManager &SM;
std::vector<TextualPPDirective> &TextualDirectives;
struct ScannedPreamble {
std::vector<Inclusion> Includes;
std::vector<TextualPPDirective> TextualDirectives;
PreambleBounds Bounds = {0, false};
/// Scans the preprocessor directives in the preamble section of the file by
/// running preprocessor over \p Contents. Returned includes do not contain
/// resolved paths. \p Cmd is used to build the compiler invocation, which might
/// stat/read files.
scanPreamble(llvm::StringRef Contents, const tooling::CompileCommand &Cmd) {
class EmptyFS : public ThreadsafeFS {
llvm::IntrusiveRefCntPtr<llvm::vfs::FileSystem> viewImpl() const override {
return new llvm::vfs::InMemoryFileSystem;
EmptyFS FS;
// Build and run Preprocessor over the preamble.
ParseInputs PI;
PI.Contents = Contents.str();
PI.CompileCommand = Cmd;
IgnoringDiagConsumer IgnoreDiags;
auto CI = buildCompilerInvocation(PI, IgnoreDiags);
if (!CI)
return error("failed to create compiler invocation");
CI->getDiagnosticOpts().IgnoreWarnings = true;
auto ContentsBuffer = llvm::MemoryBuffer::getMemBuffer(Contents);
// This means we're scanning (though not preprocessing) the preamble section
// twice. However, it's important to precisely follow the preamble bounds used
// elsewhere.
auto Bounds = ComputePreambleBounds(*CI->getLangOpts(), *ContentsBuffer, 0);
auto PreambleContents =
llvm::MemoryBuffer::getMemBufferCopy(Contents.substr(0, Bounds.Size));
auto Clang = prepareCompilerInstance(
std::move(CI), nullptr, std::move(PreambleContents),
// Provide an empty FS to prevent preprocessor from performing IO. This
// also implies missing resolved paths for includes.
FS.view(llvm::None), IgnoreDiags);
if (Clang->getFrontendOpts().Inputs.empty())
return error("compiler instance had no inputs");
// We are only interested in main file includes.
Clang->getPreprocessorOpts().SingleFileParseMode = true;
PreprocessOnlyAction Action;
if (!Action.BeginSourceFile(*Clang, Clang->getFrontendOpts().Inputs[0]))
return error("failed BeginSourceFile");
Preprocessor &PP = Clang->getPreprocessor();
IncludeStructure Includes;
ScannedPreamble SP;
SP.Bounds = Bounds;
std::make_unique<DirectiveCollector>(PP, SP.TextualDirectives));
if (llvm::Error Err = Action.Execute())
return std::move(Err);
SP.Includes = std::move(Includes.MainFileIncludes);
return SP;
const char *spellingForIncDirective(tok::PPKeywordKind IncludeDirective) {
switch (IncludeDirective) {
case tok::pp_include:
return "include";
case tok::pp_import:
return "import";
case tok::pp_include_next:
return "include_next";
llvm_unreachable("not an include directive");
// Checks whether \p FileName is a valid spelling of main file.
bool isMainFile(llvm::StringRef FileName, const SourceManager &SM) {
auto FE = SM.getFileManager().getFile(FileName);
return FE && *FE == SM.getFileEntryForID(SM.getMainFileID());
} // namespace
std::shared_ptr<const PreambleData>
buildPreamble(PathRef FileName, CompilerInvocation CI,
const ParseInputs &Inputs, bool StoreInMemory,
PreambleParsedCallback PreambleCallback) {
// Note that we don't need to copy the input contents, preamble can live
// without those.
auto ContentsBuffer =
llvm::MemoryBuffer::getMemBuffer(Inputs.Contents, FileName);
auto Bounds = ComputePreambleBounds(*CI.getLangOpts(), *ContentsBuffer, 0);
trace::Span Tracer("BuildPreamble");
SPAN_ATTACH(Tracer, "File", FileName);
std::vector<std::unique_ptr<FeatureModule::ASTListener>> ASTListeners;
if (Inputs.FeatureModules) {
for (auto &M : *Inputs.FeatureModules) {
if (auto Listener = M.astListeners())
StoreDiags PreambleDiagnostics;
[&ASTListeners](const clang::Diagnostic &D, clangd::Diag &Diag) {
[&](const auto &L) { L->sawDiagnostic(D, Diag); });
llvm::IntrusiveRefCntPtr<DiagnosticsEngine> PreambleDiagsEngine =
&PreambleDiagnostics, false);
const Config &Cfg = Config::current();
PreambleDiagnostics.setLevelAdjuster([&](DiagnosticsEngine::Level DiagLevel,
const clang::Diagnostic &Info) {
if (Cfg.Diagnostics.SuppressAll ||
isBuiltinDiagnosticSuppressed(Info.getID(), Cfg.Diagnostics.Suppress))
return DiagnosticsEngine::Ignored;
switch (Info.getID()) {
case diag::warn_no_newline_eof:
case diag::warn_cxx98_compat_no_newline_eof:
case diag::ext_no_newline_eof:
// If the preamble doesn't span the whole file, drop the no newline at
// eof warnings.
return Bounds.Size != ContentsBuffer->getBufferSize()
? DiagnosticsEngine::Level::Ignored
: DiagLevel;
return DiagLevel;
// Skip function bodies when building the preamble to speed up building
// the preamble and make it smaller.
CI.getFrontendOpts().SkipFunctionBodies = true;
// We don't want to write comment locations into PCH. They are racy and slow
// to read back. We rely on dynamic index for the comments instead.
CI.getPreprocessorOpts().WriteCommentListToPCH = false;
CppFilePreambleCallbacks CapturedInfo(FileName, PreambleCallback);
auto VFS = Inputs.TFS->view(Inputs.CompileCommand.Directory);
llvm::SmallString<32> AbsFileName(FileName);
auto StatCache = std::make_unique<PreambleFileStatusCache>(AbsFileName);
auto BuiltPreamble = PrecompiledPreamble::Build(
CI, ContentsBuffer.get(), Bounds, *PreambleDiagsEngine,
std::make_shared<PCHContainerOperations>(), StoreInMemory, CapturedInfo);
// When building the AST for the main file, we do want the function
// bodies.
CI.getFrontendOpts().SkipFunctionBodies = false;
if (BuiltPreamble) {
vlog("Built preamble of size {0} for file {1} version {2}",
BuiltPreamble->getSize(), FileName, Inputs.Version);
std::vector<Diag> Diags = PreambleDiagnostics.take();
auto Result = std::make_shared<PreambleData>(std::move(*BuiltPreamble));
Result->Version = Inputs.Version;
Result->CompileCommand = Inputs.CompileCommand;
Result->Diags = std::move(Diags);
Result->Includes = CapturedInfo.takeIncludes();
Result->Macros = CapturedInfo.takeMacros();
Result->Marks = CapturedInfo.takeMarks();
Result->CanonIncludes = CapturedInfo.takeCanonicalIncludes();
Result->StatCache = std::move(StatCache);
Result->MainIsIncludeGuarded = CapturedInfo.isMainFileIncludeGuarded();
return Result;
elog("Could not build a preamble for file {0} version {1}: {2}", FileName,
Inputs.Version, BuiltPreamble.getError().message());
return nullptr;
bool isPreambleCompatible(const PreambleData &Preamble,
const ParseInputs &Inputs, PathRef FileName,
const CompilerInvocation &CI) {
auto ContentsBuffer =
llvm::MemoryBuffer::getMemBuffer(Inputs.Contents, FileName);
auto Bounds = ComputePreambleBounds(*CI.getLangOpts(), *ContentsBuffer, 0);
auto VFS = Inputs.TFS->view(Inputs.CompileCommand.Directory);
return compileCommandsAreEqual(Inputs.CompileCommand,
Preamble.CompileCommand) &&
Preamble.Preamble.CanReuse(CI, *ContentsBuffer, Bounds, *VFS);
void escapeBackslashAndQuotes(llvm::StringRef Text, llvm::raw_ostream &OS) {
for (char C : Text) {
switch (C) {
case '\\':
case '"':
OS << '\\';
OS << C;
PreamblePatch PreamblePatch::create(llvm::StringRef FileName,
const ParseInputs &Modified,
const PreambleData &Baseline,
PatchType PatchType) {
trace::Span Tracer("CreatePreamblePatch");
SPAN_ATTACH(Tracer, "File", FileName);
assert(llvm::sys::path::is_absolute(FileName) && "relative FileName!");
// First scan preprocessor directives in Baseline and Modified. These will be
// used to figure out newly added directives in Modified. Scanning can fail,
// the code just bails out and creates an empty patch in such cases, as:
// - If scanning for Baseline fails, no knowledge of existing includes hence
// patch will contain all the includes in Modified. Leading to rebuild of
// whole preamble, which is terribly slow.
// - If scanning for Modified fails, cannot figure out newly added ones so
// there's nothing to do but generate an empty patch.
auto BaselineScan = scanPreamble(
// Contents needs to be null-terminated.
Baseline.Preamble.getContents().str(), Modified.CompileCommand);
if (!BaselineScan) {
elog("Failed to scan baseline of {0}: {1}", FileName,
return PreamblePatch::unmodified(Baseline);
auto ModifiedScan = scanPreamble(Modified.Contents, Modified.CompileCommand);
if (!ModifiedScan) {
elog("Failed to scan modified contents of {0}: {1}", FileName,
return PreamblePatch::unmodified(Baseline);
bool IncludesChanged = BaselineScan->Includes != ModifiedScan->Includes;
bool DirectivesChanged =
BaselineScan->TextualDirectives != ModifiedScan->TextualDirectives;
if ((PatchType == PatchType::MacroDirectives || !IncludesChanged) &&
return PreamblePatch::unmodified(Baseline);
PreamblePatch PP;
// This shouldn't coincide with any real file name.
llvm::SmallString<128> PatchName;
llvm::sys::path::append(PatchName, llvm::sys::path::parent_path(FileName),
PP.PatchFileName = PatchName.str().str();
PP.ModifiedBounds = ModifiedScan->Bounds;
llvm::raw_string_ostream Patch(PP.PatchContents);
// Set default filename for subsequent #line directives
Patch << "#line 0 \"";
// FileName part of a line directive is subject to backslash escaping, which
// might lead to problems on windows especially.
escapeBackslashAndQuotes(FileName, Patch);
Patch << "\"\n";
if (IncludesChanged && PatchType == PatchType::All) {
// We are only interested in newly added includes, record the ones in
// Baseline for exclusion.
llvm::DenseMap<std::pair<tok::PPKeywordKind, llvm::StringRef>,
for (const auto &Inc : Baseline.Includes.MainFileIncludes)
ExistingIncludes[{Inc.Directive, Inc.Written}] = Inc.Resolved;
// There might be includes coming from disabled regions, record these for
// exclusion too. note that we don't have resolved paths for those.
for (const auto &Inc : BaselineScan->Includes)
ExistingIncludes.try_emplace({Inc.Directive, Inc.Written});
// Calculate extra includes that needs to be inserted.
for (auto &Inc : ModifiedScan->Includes) {
auto It = ExistingIncludes.find({Inc.Directive, Inc.Written});
// Include already present in the baseline preamble. Set resolved path and
// put into preamble includes.
if (It != ExistingIncludes.end()) {
Inc.Resolved = It->second.str();
// Include is new in the modified preamble. Inject it into the patch and
// use #line to set the presumed location to where it is spelled.
auto LineCol = offsetToClangLineColumn(Modified.Contents, Inc.HashOffset);
Patch << llvm::formatv("#line {0}\n", LineCol.first);
Patch << llvm::formatv(
"#{0} {1}\n", spellingForIncDirective(Inc.Directive), Inc.Written);
if (DirectivesChanged) {
// We need to patch all the directives, since they are order dependent. e.g:
// #define BAR(X) NEW(X) // Newly introduced in Modified
// #define BAR(X) OLD(X) // Exists in the Baseline
// If we've patched only the first directive, the macro definition would've
// been wrong for the rest of the file, since patch is applied after the
// baseline preamble.
// Note that we deliberately ignore conditional directives and undefs to
// reduce complexity. The former might cause problems because scanning is
// imprecise and might pick directives from disabled regions.
for (const auto &TD : ModifiedScan->TextualDirectives) {
Patch << "#line " << TD.DirectiveLine << '\n';
Patch << TD.Text << '\n';
dlog("Created preamble patch: {0}", Patch.str());
return PP;
PreamblePatch PreamblePatch::createFullPatch(llvm::StringRef FileName,
const ParseInputs &Modified,
const PreambleData &Baseline) {
return create(FileName, Modified, Baseline, PatchType::All);
PreamblePatch PreamblePatch::createMacroPatch(llvm::StringRef FileName,
const ParseInputs &Modified,
const PreambleData &Baseline) {
return create(FileName, Modified, Baseline, PatchType::MacroDirectives);
void PreamblePatch::apply(CompilerInvocation &CI) const {
// No need to map an empty file.
if (PatchContents.empty())
auto &PPOpts = CI.getPreprocessorOpts();
auto PatchBuffer =
// we copy here to ensure contents are still valid if CI outlives the
// PreamblePatch.
llvm::MemoryBuffer::getMemBufferCopy(PatchContents, PatchFileName);
// CI will take care of the lifetime of the buffer.
PPOpts.addRemappedFile(PatchFileName, PatchBuffer.release());
// The patch will be parsed after loading the preamble ast and before parsing
// the main file.
std::vector<Inclusion> PreamblePatch::preambleIncludes() const {
return PreambleIncludes;
PreamblePatch PreamblePatch::unmodified(const PreambleData &Preamble) {
PreamblePatch PP;
PP.PreambleIncludes = Preamble.Includes.MainFileIncludes;
PP.ModifiedBounds = Preamble.Preamble.getBounds();
return PP;
SourceLocation translatePreamblePatchLocation(SourceLocation Loc,
const SourceManager &SM) {
auto DefFile = SM.getFileID(Loc);
if (auto *FE = SM.getFileEntryForID(DefFile)) {
auto IncludeLoc = SM.getIncludeLoc(DefFile);
// Preamble patch is included inside the builtin file.
if (IncludeLoc.isValid() && SM.isWrittenInBuiltinFile(IncludeLoc) &&
FE->getName().endswith(PreamblePatchHeaderName)) {
auto Presumed = SM.getPresumedLoc(Loc);
// Check that line directive is pointing at main file.
if (Presumed.isValid() && Presumed.getFileID().isInvalid() &&
isMainFile(Presumed.getFilename(), SM)) {
Loc = SM.translateLineCol(SM.getMainFileID(), Presumed.getLine(),
return Loc;
} // namespace clangd
} // namespace clang