//===--- PrecompiledPreamble.cpp - Build precompiled preambles --*- C++ -*-===//

//

// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.

// See https://llvm.org/LICENSE.txt for license information.

// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception

//

//===----------------------------------------------------------------------===//

//

// Helper class to build precompiled preamble.

//

//===----------------------------------------------------------------------===//

#include "clang/Frontend/PrecompiledPreamble.h"

#include "clang/Basic/FileManager.h"

#include "clang/Basic/LangStandard.h"

#include "clang/Frontend/CompilerInstance.h"

#include "clang/Frontend/CompilerInvocation.h"

#include "clang/Frontend/FrontendActions.h"

#include "clang/Frontend/FrontendOptions.h"

#include "clang/Lex/HeaderSearch.h"

#include "clang/Lex/Lexer.h"

#include "clang/Lex/Preprocessor.h"

#include "clang/Lex/PreprocessorOptions.h"

#include "clang/Serialization/ASTWriter.h"

#include "llvm/ADT/SmallString.h"

#include "llvm/ADT/StringSet.h"

#include "llvm/ADT/iterator_range.h"

#include "llvm/Config/llvm-config.h"

#include "llvm/Support/CrashRecoveryContext.h"

#include "llvm/Support/FileSystem.h"

#include "llvm/Support/Path.h"

#include "llvm/Support/Process.h"

#include "llvm/Support/VirtualFileSystem.h"

#include <limits>

#include <mutex>

#include <utility>

using namespace clang;

namespace {

StringRef getInMemoryPreamblePath() {

#if defined(LLVM_ON_UNIX)

  return "/__clang_tmp/___clang_inmemory_preamble___";

#elif defined(_WIN32)

  return "C:\\__clang_tmp\\___clang_inmemory_preamble___";

#else

#warning "Unknown platform. Defaulting to UNIX-style paths for in-memory PCHs"

  return "/__clang_tmp/___clang_inmemory_preamble___";

#endif

}

IntrusiveRefCntPtr<llvm::vfs::FileSystem>

createVFSOverlayForPreamblePCH(StringRef PCHFilename,

                               std::unique_ptr<llvm::MemoryBuffer> PCHBuffer,

                               IntrusiveRefCntPtr<llvm::vfs::FileSystem> VFS) {

  // We want only the PCH file from the real filesystem to be available,

  // so we create an in-memory VFS with just that and overlay it on top.

  IntrusiveRefCntPtr<llvm::vfs::InMemoryFileSystem> PCHFS(

      new llvm::vfs::InMemoryFileSystem());

  PCHFS->addFile(PCHFilename, 0, std::move(PCHBuffer));

  IntrusiveRefCntPtr<llvm::vfs::OverlayFileSystem> Overlay(

      new llvm::vfs::OverlayFileSystem(VFS));

  Overlay->pushOverlay(PCHFS);

  return Overlay;

}

class PreambleDependencyCollector : public DependencyCollector {

public:

  // We want to collect all dependencies for correctness. Avoiding the real

  // system dependencies (e.g. stl from /usr/lib) would probably be a good idea,

  // but there is no way to distinguish between those and the ones that can be

  // spuriously added by '-isystem' (e.g. to suppress warnings from those

  // headers).

  bool needSystemDependencies() override { return true; }

};

// Collects files whose existence would invalidate the preamble.

// Collecting *all* of these would make validating it too slow though, so we

// just find all the candidates for 'file not found' diagnostics.

//

// A caveat that may be significant for generated files: we'll omit files under

// search path entries whose roots don't exist when the preamble is built.

// These are pruned by InitHeaderSearch and so we don't see the search path.

// It would be nice to include them but we don't want to duplicate all the rest

// of the InitHeaderSearch logic to reconstruct them.

class MissingFileCollector : public PPCallbacks {

  llvm::StringSet<> &Out;

  const HeaderSearch &Search;

  const SourceManager &SM;

public:

  MissingFileCollector(llvm::StringSet<> &Out, const HeaderSearch &Search,

                       const SourceManager &SM)

      : Out(Out), Search(Search), SM(SM) {}

  void InclusionDirective(SourceLocation HashLoc, const Token &IncludeTok,

                          StringRef FileName, bool IsAngled,

                          CharSourceRange FilenameRange,

                          OptionalFileEntryRef File, StringRef SearchPath,

                          StringRef RelativePath, const Module *Imported,

                          SrcMgr::CharacteristicKind FileType) override {

    // File is std::nullopt if it wasn't found.

    // (We have some false negatives if PP recovered e.g. <foo> -> "foo")

    if (File)

      return;

    // If it's a rare absolute include, we know the full path already.

    if (llvm::sys::path::is_absolute(FileName)) {

      Out.insert(FileName);

      return;

    }

    // Reconstruct the filenames that would satisfy this directive...

    llvm::SmallString<256> Buf;

    auto NotFoundRelativeTo = [&](DirectoryEntryRef DE) {

      Buf = DE.getName();

      llvm::sys::path::append(Buf, FileName);

      llvm::sys::path::remove_dots(Buf, /*remove_dot_dot=*/true);

      Out.insert(Buf);

    };

    // ...relative to the including file.

    if (!IsAngled) {

      if (OptionalFileEntryRef IncludingFile =

              SM.getFileEntryRefForID(SM.getFileID(IncludeTok.getLocation())))

        if (IncludingFile->getDir())

          NotFoundRelativeTo(IncludingFile->getDir());

    }

    // ...relative to the search paths.

    for (const auto &Dir : llvm::make_range(

             IsAngled ? Search.angled_dir_begin() : Search.search_dir_begin(),

             Search.search_dir_end())) {

      // No support for frameworks or header maps yet.

      if (Dir.isNormalDir())

        NotFoundRelativeTo(*Dir.getDirRef());

    }

  }

};

/// Keeps a track of files to be deleted in destructor.

class TemporaryFiles {

public:

  // A static instance to be used by all clients.

  static TemporaryFiles &getInstance();

private:

  // Disallow constructing the class directly.

  TemporaryFiles() = default;

  // Disallow copy.

  TemporaryFiles(const TemporaryFiles &) = delete;

public:

  ~TemporaryFiles();

  /// Adds \p File to a set of tracked files.

  void addFile(StringRef File);

  /// Remove \p File from disk and from the set of tracked files.

  void removeFile(StringRef File);

private:

  std::mutex Mutex;

  llvm::StringSet<> Files;

};

TemporaryFiles &TemporaryFiles::getInstance() {

  static TemporaryFiles Instance;

  return Instance;

}

TemporaryFiles::~TemporaryFiles() {

  std::lock_guard<std::mutex> Guard(Mutex);

  for (const auto &File : Files)

    llvm::sys::fs::remove(File.getKey());

}

void TemporaryFiles::addFile(StringRef File) {

  std::lock_guard<std::mutex> Guard(Mutex);

  auto IsInserted = Files.insert(File).second;

  (void)IsInserted;

  assert(IsInserted && "File has already been added");

}

void TemporaryFiles::removeFile(StringRef File) {

  std::lock_guard<std::mutex> Guard(Mutex);

  auto WasPresent = Files.erase(File);

  (void)WasPresent;

  assert(WasPresent && "File was not tracked");

  llvm::sys::fs::remove(File);

}

// A temp file that would be deleted on destructor call. If destructor is not

// called for any reason, the file will be deleted at static objects'

// destruction.

// An assertion will fire if two TempPCHFiles are created with the same name,

// so it's not intended to be used outside preamble-handling.

class TempPCHFile {

public:

  // A main method used to construct TempPCHFile.

  static std::unique_ptr<TempPCHFile> create(StringRef StoragePath) {

    // FIXME: This is a hack so that we can override the preamble file during

    // crash-recovery testing, which is the only case where the preamble files

    // are not necessarily cleaned up.

    if (const char *TmpFile = ::getenv("CINDEXTEST_PREAMBLE_FILE"))

      return std::unique_ptr<TempPCHFile>(new TempPCHFile(TmpFile));

    llvm::SmallString<128> File;

    // Using the versions of createTemporaryFile() and

    // createUniqueFile() with a file descriptor guarantees

    // that we would never get a race condition in a multi-threaded setting

    // (i.e., multiple threads getting the same temporary path).

    int FD;

    std::error_code EC;

    if (StoragePath.empty())

      EC = llvm::sys::fs::createTemporaryFile("preamble", "pch", FD, File);

    else {

      llvm::SmallString<128> TempPath = StoragePath;

      // Use the same filename model as fs::createTemporaryFile().

      llvm::sys::path::append(TempPath, "preamble-%%%%%%.pch");

      namespace fs = llvm::sys::fs;

      // Use the same owner-only file permissions as fs::createTemporaryFile().

      EC = fs::createUniqueFile(TempPath, FD, File, fs::OF_None,

                                fs::owner_read | fs::owner_write);

    }

    if (EC)

      return nullptr;

    // We only needed to make sure the file exists, close the file right away.

    llvm::sys::Process::SafelyCloseFileDescriptor(FD);

    return std::unique_ptr<TempPCHFile>(new TempPCHFile(File.str().str()));

  }

  TempPCHFile &operator=(const TempPCHFile &) = delete;

  TempPCHFile(const TempPCHFile &) = delete;

  ~TempPCHFile() { TemporaryFiles::getInstance().removeFile(FilePath); };

  /// A path where temporary file is stored.

  llvm::StringRef getFilePath() const { return FilePath; };

private:

  TempPCHFile(std::string FilePath) : FilePath(std::move(FilePath)) {

    TemporaryFiles::getInstance().addFile(this->FilePath);

  }

  std::string FilePath;

};

class PrecompilePreambleAction : public ASTFrontendAction {

public:

  PrecompilePreambleAction(std::shared_ptr<PCHBuffer> Buffer, bool WritePCHFile,

                           PreambleCallbacks &Callbacks)

      : Buffer(std::move(Buffer)), WritePCHFile(WritePCHFile),

        Callbacks(Callbacks) {}

  std::unique_ptr<ASTConsumer> CreateASTConsumer(CompilerInstance &CI,

                                                 StringRef InFile) override;

  bool hasEmittedPreamblePCH() const { return HasEmittedPreamblePCH; }

  void setEmittedPreamblePCH(ASTWriter &Writer) {

    if (FileOS) {

      *FileOS << Buffer->Data;

      // Make sure it hits disk now.

      FileOS.reset();

    }

    this->HasEmittedPreamblePCH = true;

    Callbacks.AfterPCHEmitted(Writer);

  }

  bool BeginSourceFileAction(CompilerInstance &CI) override {

    assert(CI.getLangOpts().CompilingPCH);

    return ASTFrontendAction::BeginSourceFileAction(CI);

  }

  bool shouldEraseOutputFiles() override { return !hasEmittedPreamblePCH(); }

  bool hasCodeCompletionSupport() const override { return false; }

  bool hasASTFileSupport() const override { return false; }

  TranslationUnitKind getTranslationUnitKind() override { return TU_Prefix; }

private:

  friend class PrecompilePreambleConsumer;

  bool HasEmittedPreamblePCH = false;

  std::shared_ptr<PCHBuffer> Buffer;

  bool WritePCHFile; // otherwise the PCH is written into the PCHBuffer only.

  std::unique_ptr<llvm::raw_pwrite_stream> FileOS; // null if in-memory

  PreambleCallbacks &Callbacks;

};

class PrecompilePreambleConsumer : public PCHGenerator {

public:

  PrecompilePreambleConsumer(PrecompilePreambleAction &Action,

                             const Preprocessor &PP,

                             InMemoryModuleCache &ModuleCache,

                             StringRef isysroot,

                             std::shared_ptr<PCHBuffer> Buffer)

      : PCHGenerator(PP, ModuleCache, "", isysroot, std::move(Buffer),

                     ArrayRef<std::shared_ptr<ModuleFileExtension>>(),

                     /*AllowASTWithErrors=*/true),

        Action(Action) {}

  bool HandleTopLevelDecl(DeclGroupRef DG) override {

    Action.Callbacks.HandleTopLevelDecl(DG);

    return true;

  }

  void HandleTranslationUnit(ASTContext &Ctx) override {

    PCHGenerator::HandleTranslationUnit(Ctx);

    if (!hasEmittedPCH())

      return;

    Action.setEmittedPreamblePCH(getWriter());

  }

  bool shouldSkipFunctionBody(Decl *D) override {

    return Action.Callbacks.shouldSkipFunctionBody(D);

  }

private:

  PrecompilePreambleAction &Action;

};

std::unique_ptr<ASTConsumer>

PrecompilePreambleAction::CreateASTConsumer(CompilerInstance &CI,

                                            StringRef InFile) {

  std::string Sysroot;

  if (!GeneratePCHAction::ComputeASTConsumerArguments(CI, Sysroot))

    return nullptr;

  if (WritePCHFile) {

    std::string OutputFile; // unused

    FileOS = GeneratePCHAction::CreateOutputFile(CI, InFile, OutputFile);

    if (!FileOS)

      return nullptr;

  }

  if (!CI.getFrontendOpts().RelocatablePCH)

    Sysroot.clear();

  return std::make_unique<PrecompilePreambleConsumer>(

      *this, CI.getPreprocessor(), CI.getModuleCache(), Sysroot, Buffer);

}

template <class T> bool moveOnNoError(llvm::ErrorOr<T> Val, T &Output) {

  if (!Val)

    return false;

  Output = std::move(*Val);

  return true;

}

} // namespace

PreambleBounds clang::ComputePreambleBounds(const LangOptions &LangOpts,

                                            const llvm::MemoryBufferRef &Buffer,

                                            unsigned MaxLines) {

  return Lexer::ComputePreamble(Buffer.getBuffer(), LangOpts, MaxLines);

}

class PrecompiledPreamble::PCHStorage {

public:

  static std::unique_ptr<PCHStorage> file(std::unique_ptr<TempPCHFile> File) {

    assert(File);

    std::unique_ptr<PCHStorage> S(new PCHStorage());

    S->File = std::move(File);

    return S;

  }

  static std::unique_ptr<PCHStorage> inMemory(std::shared_ptr<PCHBuffer> Buf) {

    std::unique_ptr<PCHStorage> S(new PCHStorage());

    S->Memory = std::move(Buf);

    return S;

  }

  enum class Kind { InMemory, TempFile };

  Kind getKind() const {

    if (Memory)

      return Kind::InMemory;

    if (File)

      return Kind::TempFile;

    llvm_unreachable("Neither Memory nor File?");

  }

  llvm::StringRef filePath() const {

    assert(getKind() == Kind::TempFile);

    return File->getFilePath();

  }

  llvm::StringRef memoryContents() const {

    assert(getKind() == Kind::InMemory);

    return StringRef(Memory->Data.data(), Memory->Data.size());

  }

  // Shrink in-memory buffers to fit.

  // This incurs a copy, but preambles tend to be long-lived.

  // Only safe to call once nothing can alias the buffer.

  void shrink() {

    if (!Memory)

      return;

    Memory->Data = decltype(Memory->Data)(Memory->Data);

  }

private:

  PCHStorage() = default;

  PCHStorage(const PCHStorage &) = delete;

  PCHStorage &operator=(const PCHStorage &) = delete;

  std::shared_ptr<PCHBuffer> Memory;

  std::unique_ptr<TempPCHFile> File;

};

PrecompiledPreamble::~PrecompiledPreamble() = default;

PrecompiledPreamble::PrecompiledPreamble(PrecompiledPreamble &&) = default;

PrecompiledPreamble &

PrecompiledPreamble::operator=(PrecompiledPreamble &&) = default;

llvm::ErrorOr<PrecompiledPreamble> PrecompiledPreamble::Build(

    const CompilerInvocation &Invocation,

    const llvm::MemoryBuffer *MainFileBuffer, PreambleBounds Bounds,

    DiagnosticsEngine &Diagnostics,

    IntrusiveRefCntPtr<llvm::vfs::FileSystem> VFS,

    std::shared_ptr<PCHContainerOperations> PCHContainerOps, bool StoreInMemory,

    StringRef StoragePath, PreambleCallbacks &Callbacks) {

  assert(VFS && "VFS is null");

  auto PreambleInvocation = std::make_shared<CompilerInvocation>(Invocation);

  FrontendOptions &FrontendOpts = PreambleInvocation->getFrontendOpts();

  PreprocessorOptions &PreprocessorOpts =

      PreambleInvocation->getPreprocessorOpts();

  std::shared_ptr<PCHBuffer> Buffer = std::make_shared<PCHBuffer>();

  std::unique_ptr<PCHStorage> Storage;

  if (StoreInMemory) {

    Storage = PCHStorage::inMemory(Buffer);

  } else {

    // Create a temporary file for the precompiled preamble. In rare

    // circumstances, this can fail.

    std::unique_ptr<TempPCHFile> PreamblePCHFile =

        TempPCHFile::create(StoragePath);

    if (!PreamblePCHFile)

      return BuildPreambleError::CouldntCreateTempFile;

    Storage = PCHStorage::file(std::move(PreamblePCHFile));

  }

  // Save the preamble text for later; we'll need to compare against it for

  // subsequent reparses.

  std::vector<char> PreambleBytes(MainFileBuffer->getBufferStart(),

                                  MainFileBuffer->getBufferStart() +

                                      Bounds.Size);

  bool PreambleEndsAtStartOfLine = Bounds.PreambleEndsAtStartOfLine;

  // Tell the compiler invocation to generate a temporary precompiled header.

  FrontendOpts.ProgramAction = frontend::GeneratePCH;

  FrontendOpts.OutputFile = std::string(

      StoreInMemory ? getInMemoryPreamblePath() : Storage->filePath());

  PreprocessorOpts.PrecompiledPreambleBytes.first = 0;

  PreprocessorOpts.PrecompiledPreambleBytes.second = false;

  // Inform preprocessor to record conditional stack when building the preamble.

  PreprocessorOpts.GeneratePreamble = true;

  // Create the compiler instance to use for building the precompiled preamble.

  std::unique_ptr<CompilerInstance> Clang(

      new CompilerInstance(std::move(PCHContainerOps)));

  // Recover resources if we crash before exiting this method.

  llvm::CrashRecoveryContextCleanupRegistrar<CompilerInstance> CICleanup(

      Clang.get());

  Clang->setInvocation(std::move(PreambleInvocation));

  Clang->setDiagnostics(&Diagnostics);

  // Create the target instance.

  if (!Clang->createTarget())

    return BuildPreambleError::CouldntCreateTargetInfo;

  if (Clang->getFrontendOpts().Inputs.size() != 1 ||

      Clang->getFrontendOpts().Inputs[0].getKind().getFormat() !=

          InputKind::Source ||

      Clang->getFrontendOpts().Inputs[0].getKind().getLanguage() ==

          Language::LLVM_IR) {

    return BuildPreambleError::BadInputs;

  }

  // Clear out old caches and data.

  Diagnostics.Reset();

  ProcessWarningOptions(Diagnostics, Clang->getDiagnosticOpts());

  VFS =

      createVFSFromCompilerInvocation(Clang->getInvocation(), Diagnostics, VFS);

  // Create a file manager object to provide access to and cache the filesystem.

  Clang->setFileManager(new FileManager(Clang->getFileSystemOpts(), VFS));

  // Create the source manager.

  Clang->setSourceManager(

      new SourceManager(Diagnostics, Clang->getFileManager()));

  auto PreambleDepCollector = std::make_shared<PreambleDependencyCollector>();

  Clang->addDependencyCollector(PreambleDepCollector);

  Clang->getLangOpts().CompilingPCH = true;

  // Remap the main source file to the preamble buffer.

  StringRef MainFilePath = FrontendOpts.Inputs[0].getFile();

  auto PreambleInputBuffer = llvm::MemoryBuffer::getMemBufferCopy(

      MainFileBuffer->getBuffer().slice(0, Bounds.Size), MainFilePath);

  if (PreprocessorOpts.RetainRemappedFileBuffers) {

    // MainFileBuffer will be deleted by unique_ptr after leaving the method.

    PreprocessorOpts.addRemappedFile(MainFilePath, PreambleInputBuffer.get());

  } else {

    // In that case, remapped buffer will be deleted by CompilerInstance on

    // BeginSourceFile, so we call release() to avoid double deletion.

    PreprocessorOpts.addRemappedFile(MainFilePath,

                                     PreambleInputBuffer.release());

  }

  auto Act = std::make_unique<PrecompilePreambleAction>(

      std::move(Buffer),

      /*WritePCHFile=*/Storage->getKind() == PCHStorage::Kind::TempFile,

      Callbacks);

  if (!Act->BeginSourceFile(*Clang.get(), Clang->getFrontendOpts().Inputs[0]))

    return BuildPreambleError::BeginSourceFileFailed;

  // Performed after BeginSourceFile to ensure Clang->Preprocessor can be

  // referenced in the callback.

  Callbacks.BeforeExecute(*Clang);

  std::unique_ptr<PPCallbacks> DelegatedPPCallbacks =

      Callbacks.createPPCallbacks();

  if (DelegatedPPCallbacks)

    Clang->getPreprocessor().addPPCallbacks(std::move(DelegatedPPCallbacks));

  if (auto CommentHandler = Callbacks.getCommentHandler())

    Clang->getPreprocessor().addCommentHandler(CommentHandler);

  llvm::StringSet<> MissingFiles;

  Clang->getPreprocessor().addPPCallbacks(

      std::make_unique<MissingFileCollector>(

          MissingFiles, Clang->getPreprocessor().getHeaderSearchInfo(),

          Clang->getSourceManager()));

  if (llvm::Error Err = Act->Execute())

    return errorToErrorCode(std::move(Err));

  // Run the callbacks.

  Callbacks.AfterExecute(*Clang);

  Act->EndSourceFile();

  if (!Act->hasEmittedPreamblePCH())

    return BuildPreambleError::CouldntEmitPCH;

  Act.reset(); // Frees the PCH buffer, unless Storage keeps it in memory.

  // Keep track of all of the files that the source manager knows about,

  // so we can verify whether they have changed or not.

  llvm::StringMap<PrecompiledPreamble::PreambleFileHash> FilesInPreamble;

  SourceManager &SourceMgr = Clang->getSourceManager();

  for (auto &Filename : PreambleDepCollector->getDependencies()) {

    auto MaybeFile = Clang->getFileManager().getOptionalFileRef(Filename);

    if (!MaybeFile ||

        MaybeFile == SourceMgr.getFileEntryRefForID(SourceMgr.getMainFileID()))

      continue;

    auto File = *MaybeFile;

    if (time_t ModTime = File.getModificationTime()) {

      FilesInPreamble[File.getName()] =

          PrecompiledPreamble::PreambleFileHash::createForFile(File.getSize(),

                                                               ModTime);

    } else {

      llvm::MemoryBufferRef Buffer =

          SourceMgr.getMemoryBufferForFileOrFake(File);

      FilesInPreamble[File.getName()] =

          PrecompiledPreamble::PreambleFileHash::createForMemoryBuffer(Buffer);

    }

  }

  // Shrinking the storage requires extra temporary memory.

  // Destroying clang first reduces peak memory usage.

  CICleanup.unregister();

  Clang.reset();

  Storage->shrink();

  return PrecompiledPreamble(

      std::move(Storage), std::move(PreambleBytes), PreambleEndsAtStartOfLine,

      std::move(FilesInPreamble), std::move(MissingFiles));

}

PreambleBounds PrecompiledPreamble::getBounds() const {

  return PreambleBounds(PreambleBytes.size(), PreambleEndsAtStartOfLine);

}

std::size_t PrecompiledPreamble::getSize() const {

  switch (Storage->getKind()) {

  case PCHStorage::Kind::InMemory:

    return Storage->memoryContents().size();

  case PCHStorage::Kind::TempFile: {

    uint64_t Result;

    if (llvm::sys::fs::file_size(Storage->filePath(), Result))

      return 0;

    assert(Result <= std::numeric_limits<std::size_t>::max() &&

           "file size did not fit into size_t");

    return Result;

  }

  }

  llvm_unreachable("Unhandled storage kind");

}

bool PrecompiledPreamble::CanReuse(const CompilerInvocation &Invocation,

                                   const llvm::MemoryBufferRef &MainFileBuffer,

                                   PreambleBounds Bounds,

                                   llvm::vfs::FileSystem &VFS) const {

  assert(

      Bounds.Size <= MainFileBuffer.getBufferSize() &&

      "Buffer is too large. Bounds were calculated from a different buffer?");

  auto PreambleInvocation = std::make_shared<CompilerInvocation>(Invocation);

  PreprocessorOptions &PreprocessorOpts =

      PreambleInvocation->getPreprocessorOpts();

  // We've previously computed a preamble. Check whether we have the same

  // preamble now that we did before, and that there's enough space in

  // the main-file buffer within the precompiled preamble to fit the

  // new main file.

  if (PreambleBytes.size() != Bounds.Size ||

      PreambleEndsAtStartOfLine != Bounds.PreambleEndsAtStartOfLine ||

      !std::equal(PreambleBytes.begin(), PreambleBytes.end(),

                  MainFileBuffer.getBuffer().begin()))

    return false;

  // The preamble has not changed. We may be able to re-use the precompiled

  // preamble.

  // Check that none of the files used by the preamble have changed.

  // First, make a record of those files that have been overridden via

  // remapping or unsaved_files.

  std::map<llvm::sys::fs::UniqueID, PreambleFileHash> OverriddenFiles;

  llvm::StringSet<> OverriddenAbsPaths; // Either by buffers or files.

  for (const auto &R : PreprocessorOpts.RemappedFiles) {

    llvm::vfs::Status Status;

    if (!moveOnNoError(VFS.status(R.second), Status)) {

      // If we can't stat the file we're remapping to, assume that something

      // horrible happened.

      return false;

    }

    // If a mapped file was previously missing, then it has changed.

    llvm::SmallString<128> MappedPath(R.first);

    if (!VFS.makeAbsolute(MappedPath))

      OverriddenAbsPaths.insert(MappedPath);

    OverriddenFiles[Status.getUniqueID()] = PreambleFileHash::createForFile(

        Status.getSize(), llvm::sys::toTimeT(Status.getLastModificationTime()));

  }

  // OverridenFileBuffers tracks only the files not found in VFS.

  llvm::StringMap<PreambleFileHash> OverridenFileBuffers;

  for (const auto &RB : PreprocessorOpts.RemappedFileBuffers) {

    const PrecompiledPreamble::PreambleFileHash PreambleHash =

        PreambleFileHash::createForMemoryBuffer(RB.second->getMemBufferRef());

    llvm::vfs::Status Status;

    if (moveOnNoError(VFS.status(RB.first), Status))

      OverriddenFiles[Status.getUniqueID()] = PreambleHash;

    else

      OverridenFileBuffers[RB.first] = PreambleHash;

    llvm::SmallString<128> MappedPath(RB.first);

    if (!VFS.makeAbsolute(MappedPath))

      OverriddenAbsPaths.insert(MappedPath);

  }

  // Check whether anything has changed.

  for (const auto &F : FilesInPreamble) {

    auto OverridenFileBuffer = OverridenFileBuffers.find(F.first());

    if (OverridenFileBuffer != OverridenFileBuffers.end()) {

      // The file's buffer was remapped and the file was not found in VFS.

      // Check whether it matches up with the previous mapping.

      if (OverridenFileBuffer->second != F.second)

        return false;

      continue;

    }

    llvm::vfs::Status Status;

    if (!moveOnNoError(VFS.status(F.first()), Status)) {

      // If the file's buffer is not remapped and we can't stat it,

      // assume that something horrible happened.

      return false;

    }

    std::map<llvm::sys::fs::UniqueID, PreambleFileHash>::iterator Overridden =

        OverriddenFiles.find(Status.getUniqueID());

    if (Overridden != OverriddenFiles.end()) {

      // This file was remapped; check whether the newly-mapped file

      // matches up with the previous mapping.

      if (Overridden->second != F.second)

        return false;

      continue;

    }

    // Neither the file's buffer nor the file itself was remapped;

    // check whether it has changed on disk.

    if (Status.getSize() != uint64_t(F.second.Size) ||

        llvm::sys::toTimeT(Status.getLastModificationTime()) !=

            F.second.ModTime)

      return false;

  }

  for (const auto &F : MissingFiles) {

    // A missing file may be "provided" by an override buffer or file.

    if (OverriddenAbsPaths.count(F.getKey()))

      return false;

    // If a file previously recorded as missing exists as a regular file, then

    // consider the preamble out-of-date.

    if (auto Status = VFS.status(F.getKey())) {

      if (Status->isRegularFile())

        return false;

    }

  }

  return true;

}

void PrecompiledPreamble::AddImplicitPreamble(

    CompilerInvocation &CI, IntrusiveRefCntPtr<llvm::vfs::FileSystem> &VFS,

    llvm::MemoryBuffer *MainFileBuffer) const {

  PreambleBounds Bounds(PreambleBytes.size(), PreambleEndsAtStartOfLine);

  configurePreamble(Bounds, CI, VFS, MainFileBuffer);

}

void PrecompiledPreamble::OverridePreamble(

    CompilerInvocation &CI, IntrusiveRefCntPtr<llvm::vfs::FileSystem> &VFS,

    llvm::MemoryBuffer *MainFileBuffer) const {

  auto Bounds = ComputePreambleBounds(CI.getLangOpts(), *MainFileBuffer, 0);

  configurePreamble(Bounds, CI, VFS, MainFileBuffer);

}

PrecompiledPreamble::PrecompiledPreamble(

    std::unique_ptr<PCHStorage> Storage, std::vector<char> PreambleBytes,

    bool PreambleEndsAtStartOfLine,

    llvm::StringMap<PreambleFileHash> FilesInPreamble,

    llvm::StringSet<> MissingFiles)

    : Storage(std::move(Storage)), FilesInPreamble(std::move(FilesInPreamble)),

      MissingFiles(std::move(MissingFiles)),

      PreambleBytes(std::move(PreambleBytes)),

      PreambleEndsAtStartOfLine(PreambleEndsAtStartOfLine) {

  assert(this->Storage != nullptr);

}

PrecompiledPreamble::PreambleFileHash

PrecompiledPreamble::PreambleFileHash::createForFile(off_t Size,

                                                     time_t ModTime) {

  PreambleFileHash Result;

  Result.Size = Size;

  Result.ModTime = ModTime;

  Result.MD5 = {};

  return Result;

}

PrecompiledPreamble::PreambleFileHash

PrecompiledPreamble::PreambleFileHash::createForMemoryBuffer(

    const llvm::MemoryBufferRef &Buffer) {

  PreambleFileHash Result;

  Result.Size = Buffer.getBufferSize();

  Result.ModTime = 0;

  llvm::MD5 MD5Ctx;

  MD5Ctx.update(Buffer.getBuffer().data());

  MD5Ctx.final(Result.MD5);

  return Result;

}

void PrecompiledPreamble::configurePreamble(

    PreambleBounds Bounds, CompilerInvocation &CI,

    IntrusiveRefCntPtr<llvm::vfs::FileSystem> &VFS,

    llvm::MemoryBuffer *MainFileBuffer) const {

  assert(VFS);

  auto &PreprocessorOpts = CI.getPreprocessorOpts();

  // Remap main file to point to MainFileBuffer.

  auto MainFilePath = CI.getFrontendOpts().Inputs[0].getFile();

  PreprocessorOpts.addRemappedFile(MainFilePath, MainFileBuffer);

  // Configure ImpicitPCHInclude.

  PreprocessorOpts.PrecompiledPreambleBytes.first = Bounds.Size;

  PreprocessorOpts.PrecompiledPreambleBytes.second =

      Bounds.PreambleEndsAtStartOfLine;

  PreprocessorOpts.DisablePCHOrModuleValidation =

      DisableValidationForModuleKind::PCH;

  // Don't bother generating the long version of the predefines buffer.

  // The preamble is going to overwrite it anyway.

  PreprocessorOpts.UsePredefines = false;

  setupPreambleStorage(*Storage, PreprocessorOpts, VFS);

}

void PrecompiledPreamble::setupPreambleStorage(

    const PCHStorage &Storage, PreprocessorOptions &PreprocessorOpts,

    IntrusiveRefCntPtr<llvm::vfs::FileSystem> &VFS) {

  if (Storage.getKind() == PCHStorage::Kind::TempFile) {

    llvm::StringRef PCHPath = Storage.filePath();

    PreprocessorOpts.ImplicitPCHInclude = PCHPath.str();

    // Make sure we can access the PCH file even if we're using a VFS

    IntrusiveRefCntPtr<llvm::vfs::FileSystem> RealFS =

        llvm::vfs::getRealFileSystem();

    if (VFS == RealFS || VFS->exists(PCHPath))

      return;

    auto Buf = RealFS->getBufferForFile(PCHPath);

    if (!Buf) {

      // We can't read the file even from RealFS, this is clearly an error,

      // but we'll just leave the current VFS as is and let clang's code

      // figure out what to do with missing PCH.

      return;

    }

    // We have a slight inconsistency here -- we're using the VFS to

    // read files, but the PCH was generated in the real file system.

    VFS = createVFSOverlayForPreamblePCH(PCHPath, std::move(*Buf), VFS);

  } else {

    assert(Storage.getKind() == PCHStorage::Kind::InMemory);

    // For in-memory preamble, we have to provide a VFS overlay that makes it

    // accessible.

    StringRef PCHPath = getInMemoryPreamblePath();

    PreprocessorOpts.ImplicitPCHInclude = std::string(PCHPath);

    auto Buf = llvm::MemoryBuffer::getMemBuffer(

        Storage.memoryContents(), PCHPath, /*RequiresNullTerminator=*/false);

    VFS = createVFSOverlayForPreamblePCH(PCHPath, std::move(Buf), VFS);

  }

}

void PreambleCallbacks::BeforeExecute(CompilerInstance &CI) {}

void PreambleCallbacks::AfterExecute(CompilerInstance &CI) {}

void PreambleCallbacks::AfterPCHEmitted(ASTWriter &Writer) {}

void PreambleCallbacks::HandleTopLevelDecl(DeclGroupRef DG) {}

std::unique_ptr<PPCallbacks> PreambleCallbacks::createPPCallbacks() {

  return nullptr;

}

CommentHandler *PreambleCallbacks::getCommentHandler() { return nullptr; }

static llvm::ManagedStatic<BuildPreambleErrorCategory> BuildPreambleErrCategory;

std::error_code clang::make_error_code(BuildPreambleError Error) {

  return std::error_code(static_cast<int>(Error), *BuildPreambleErrCategory);

}

const char *BuildPreambleErrorCategory::name() const noexcept {

  return "build-preamble.error";

}

std::string BuildPreambleErrorCategory::message(int condition) const {

  switch (static_cast<BuildPreambleError>(condition)) {

  case BuildPreambleError::CouldntCreateTempFile:

    return "Could not create temporary file for PCH";

  case BuildPreambleError::CouldntCreateTargetInfo:

    return "CreateTargetInfo() return null";

  case BuildPreambleError::BeginSourceFileFailed:

    return "BeginSourceFile() return an error";

  case BuildPreambleError::CouldntEmitPCH:

    return "Could not emit PCH";

  case BuildPreambleError::BadInputs:

    return "Command line arguments must contain exactly one source file";

  }

  llvm_unreachable("unexpected BuildPreambleError");

}