clang-tools-extra/clangd/ClangdUnit.cpp

//===--- ClangdUnit.cpp -----------------------------------------*- C++-*-===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===---------------------------------------------------------------------===//

#include "ClangdUnit.h"

#include "Compiler.h"
#include "Logger.h"
#include "Trace.h"
#include "clang/Frontend/CompilerInstance.h"
#include "clang/Frontend/CompilerInvocation.h"
#include "clang/Frontend/FrontendActions.h"
#include "clang/Frontend/Utils.h"
#include "clang/Index/IndexDataConsumer.h"
#include "clang/Index/IndexingAction.h"
#include "clang/Lex/Lexer.h"
#include "clang/Lex/MacroInfo.h"
#include "clang/Lex/Preprocessor.h"
#include "clang/Sema/Sema.h"
#include "clang/Serialization/ASTWriter.h"
#include "clang/Tooling/CompilationDatabase.h"
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/Support/CrashRecoveryContext.h"
#include "llvm/Support/Format.h"

#include <algorithm>
#include <chrono>

using namespace clang::clangd;
using namespace clang;

namespace {

class DeclTrackingASTConsumer : public ASTConsumer {
public:
  DeclTrackingASTConsumer(std::vector<const Decl *> &TopLevelDecls)
      : TopLevelDecls(TopLevelDecls) {}

  bool HandleTopLevelDecl(DeclGroupRef DG) override {
    for (const Decl *D : DG) {
      // ObjCMethodDecl are not actually top-level decls.
      if (isa<ObjCMethodDecl>(D))
        continue;

      TopLevelDecls.push_back(D);
    }
    return true;
  }

private:
  std::vector<const Decl *> &TopLevelDecls;
};

class ClangdFrontendAction : public SyntaxOnlyAction {
public:
  std::vector<const Decl *> takeTopLevelDecls() {
    return std::move(TopLevelDecls);
  }

protected:
  std::unique_ptr<ASTConsumer> CreateASTConsumer(CompilerInstance &CI,
                                                 StringRef InFile) override {
    return llvm::make_unique<DeclTrackingASTConsumer>(/*ref*/ TopLevelDecls);
  }

private:
  std::vector<const Decl *> TopLevelDecls;
};

class CppFilePreambleCallbacks : public PreambleCallbacks {
public:
  std::vector<serialization::DeclID> takeTopLevelDeclIDs() {
    return std::move(TopLevelDeclIDs);
  }

  void AfterPCHEmitted(ASTWriter &Writer) override {
    TopLevelDeclIDs.reserve(TopLevelDecls.size());
    for (Decl *D : TopLevelDecls) {
      // Invalid top-level decls may not have been serialized.
      if (D->isInvalidDecl())
        continue;
      TopLevelDeclIDs.push_back(Writer.getDeclID(D));
    }
  }

  void HandleTopLevelDecl(DeclGroupRef DG) override {
    for (Decl *D : DG) {
      if (isa<ObjCMethodDecl>(D))
        continue;
      TopLevelDecls.push_back(D);
    }
  }

private:
  std::vector<Decl *> TopLevelDecls;
  std::vector<serialization::DeclID> TopLevelDeclIDs;
};

/// Convert from clang diagnostic level to LSP severity.
static int getSeverity(DiagnosticsEngine::Level L) {
  switch (L) {
  case DiagnosticsEngine::Remark:
    return 4;
  case DiagnosticsEngine::Note:
    return 3;
  case DiagnosticsEngine::Warning:
    return 2;
  case DiagnosticsEngine::Fatal:
  case DiagnosticsEngine::Error:
    return 1;
  case DiagnosticsEngine::Ignored:
    return 0;
  }
  llvm_unreachable("Unknown diagnostic level!");
}

llvm::Optional<DiagWithFixIts> toClangdDiag(const StoredDiagnostic &D) {
  auto Location = D.getLocation();
  if (!Location.isValid() || !Location.getManager().isInMainFile(Location))
    return llvm::None;

  Position P;
  P.line = Location.getSpellingLineNumber() - 1;
  P.character = Location.getSpellingColumnNumber();
  Range R = {P, P};
  clangd::Diagnostic Diag = {R, getSeverity(D.getLevel()), D.getMessage()};

  llvm::SmallVector<tooling::Replacement, 1> FixItsForDiagnostic;
  for (const FixItHint &Fix : D.getFixIts()) {
    FixItsForDiagnostic.push_back(clang::tooling::Replacement(
        Location.getManager(), Fix.RemoveRange, Fix.CodeToInsert));
  }
  return DiagWithFixIts{Diag, std::move(FixItsForDiagnostic)};
}

class StoreDiagsConsumer : public DiagnosticConsumer {
public:
  StoreDiagsConsumer(std::vector<DiagWithFixIts> &Output) : Output(Output) {}

  void HandleDiagnostic(DiagnosticsEngine::Level DiagLevel,
                        const clang::Diagnostic &Info) override {
    DiagnosticConsumer::HandleDiagnostic(DiagLevel, Info);

    if (auto convertedDiag = toClangdDiag(StoredDiagnostic(DiagLevel, Info)))
      Output.push_back(std::move(*convertedDiag));
  }

private:
  std::vector<DiagWithFixIts> &Output;
};

template <class T> bool futureIsReady(std::shared_future<T> const &Future) {
  return Future.wait_for(std::chrono::seconds(0)) == std::future_status::ready;
}

} // namespace

void clangd::dumpAST(ParsedAST &AST, llvm::raw_ostream &OS) {
  AST.getASTContext().getTranslationUnitDecl()->dump(OS, true);
}

llvm::Optional<ParsedAST>
ParsedAST::Build(std::unique_ptr<clang::CompilerInvocation> CI,
                 std::shared_ptr<const PreambleData> Preamble,
                 std::unique_ptr<llvm::MemoryBuffer> Buffer,
                 std::shared_ptr<PCHContainerOperations> PCHs,
                 IntrusiveRefCntPtr<vfs::FileSystem> VFS,
                 clangd::Logger &Logger) {

  std::vector<DiagWithFixIts> ASTDiags;
  StoreDiagsConsumer UnitDiagsConsumer(/*ref*/ ASTDiags);

  const PrecompiledPreamble *PreamblePCH =
      Preamble ? &Preamble->Preamble : nullptr;
  auto Clang = prepareCompilerInstance(
      std::move(CI), PreamblePCH, std::move(Buffer), std::move(PCHs),
      std::move(VFS), /*ref*/ UnitDiagsConsumer);

  // Recover resources if we crash before exiting this method.
  llvm::CrashRecoveryContextCleanupRegistrar<CompilerInstance> CICleanup(
      Clang.get());

  auto Action = llvm::make_unique<ClangdFrontendAction>();
  const FrontendInputFile &MainInput = Clang->getFrontendOpts().Inputs[0];
  if (!Action->BeginSourceFile(*Clang, MainInput)) {
    Logger.log("BeginSourceFile() failed when building AST for " +
               MainInput.getFile());
    return llvm::None;
  }
  if (!Action->Execute())
    Logger.log("Execute() failed when building AST for " + MainInput.getFile());

  // UnitDiagsConsumer is local, we can not store it in CompilerInstance that
  // has a longer lifetime.
  Clang->getDiagnostics().setClient(new IgnoreDiagnostics);

  std::vector<const Decl *> ParsedDecls = Action->takeTopLevelDecls();
  return ParsedAST(std::move(Preamble), std::move(Clang), std::move(Action),
                   std::move(ParsedDecls), std::move(ASTDiags));
}

namespace {

SourceLocation getMacroArgExpandedLocation(const SourceManager &Mgr,
                                           const FileEntry *FE,
                                           unsigned Offset) {
  SourceLocation FileLoc = Mgr.translateFileLineCol(FE, 1, 1);
  return Mgr.getMacroArgExpandedLocation(FileLoc.getLocWithOffset(Offset));
}

SourceLocation getMacroArgExpandedLocation(const SourceManager &Mgr,
                                           const FileEntry *FE, Position Pos) {
  SourceLocation InputLoc =
      Mgr.translateFileLineCol(FE, Pos.line + 1, Pos.character + 1);
  return Mgr.getMacroArgExpandedLocation(InputLoc);
}

/// Finds declarations locations that a given source location refers to.
class DeclarationAndMacrosFinder : public index::IndexDataConsumer {
  std::vector<const Decl *> Decls;
  std::vector<const MacroInfo *> MacroInfos;
  const SourceLocation &SearchedLocation;
  const ASTContext &AST;
  Preprocessor &PP;

public:
  DeclarationAndMacrosFinder(raw_ostream &OS,
                             const SourceLocation &SearchedLocation,
                             ASTContext &AST, Preprocessor &PP)
      : SearchedLocation(SearchedLocation), AST(AST), PP(PP) {}

  std::vector<const Decl *> takeDecls() {
    // Don't keep the same declaration multiple times.
    // This can happen when nodes in the AST are visited twice.
    std::sort(Decls.begin(), Decls.end());
    auto Last = std::unique(Decls.begin(), Decls.end());
    Decls.erase(Last, Decls.end());
    return std::move(Decls);
  }

  std::vector<const MacroInfo *> takeMacroInfos() {
    // Don't keep the same Macro info multiple times.
    std::sort(MacroInfos.begin(), MacroInfos.end());
    auto Last = std::unique(MacroInfos.begin(), MacroInfos.end());
    MacroInfos.erase(Last, MacroInfos.end());
    return std::move(MacroInfos);
  }

  bool
  handleDeclOccurence(const Decl *D, index::SymbolRoleSet Roles,
                      ArrayRef<index::SymbolRelation> Relations, FileID FID,
                      unsigned Offset,
                      index::IndexDataConsumer::ASTNodeInfo ASTNode) override {
    if (isSearchedLocation(FID, Offset))
      Decls.push_back(D);
    return true;
  }

private:
  bool isSearchedLocation(FileID FID, unsigned Offset) const {
    const SourceManager &SourceMgr = AST.getSourceManager();
    return SourceMgr.getFileOffset(SearchedLocation) == Offset &&
           SourceMgr.getFileID(SearchedLocation) == FID;
  }

  void finish() override {
    // Also handle possible macro at the searched location.
    Token Result;
    if (!Lexer::getRawToken(SearchedLocation, Result, AST.getSourceManager(),
                            AST.getLangOpts(), false)) {
      if (Result.is(tok::raw_identifier)) {
        PP.LookUpIdentifierInfo(Result);
      }
      IdentifierInfo *IdentifierInfo = Result.getIdentifierInfo();
      if (IdentifierInfo && IdentifierInfo->hadMacroDefinition()) {
        std::pair<FileID, unsigned int> DecLoc =
            AST.getSourceManager().getDecomposedExpansionLoc(SearchedLocation);
        // Get the definition just before the searched location so that a macro
        // referenced in a '#undef MACRO' can still be found.
        SourceLocation BeforeSearchedLocation = getMacroArgExpandedLocation(
            AST.getSourceManager(),
            AST.getSourceManager().getFileEntryForID(DecLoc.first),
            DecLoc.second - 1);
        MacroDefinition MacroDef =
            PP.getMacroDefinitionAtLoc(IdentifierInfo, BeforeSearchedLocation);
        MacroInfo *MacroInf = MacroDef.getMacroInfo();
        if (MacroInf) {
          MacroInfos.push_back(MacroInf);
        }
      }
    }
  }
};

/// Finds document highlights that a given list of declarations refers to.
class DocumentHighlightsFinder : public index::IndexDataConsumer {
  std::vector<const Decl *> &Decls;
  std::vector<DocumentHighlight> DocumentHighlights;
  const ASTContext &AST;

public:
  DocumentHighlightsFinder(raw_ostream &OS, ASTContext &AST, Preprocessor &PP,
                           std::vector<const Decl *> &Decls)
      : Decls(Decls), AST(AST) {}
  std::vector<DocumentHighlight> takeHighlights() {
    // Don't keep the same highlight multiple times.
    // This can happen when nodes in the AST are visited twice.
    std::sort(DocumentHighlights.begin(), DocumentHighlights.end());
    auto Last =
        std::unique(DocumentHighlights.begin(), DocumentHighlights.end());
    DocumentHighlights.erase(Last, DocumentHighlights.end());
    return std::move(DocumentHighlights);
  }

  bool
  handleDeclOccurence(const Decl *D, index::SymbolRoleSet Roles,
                      ArrayRef<index::SymbolRelation> Relations, FileID FID,
                      unsigned Offset,
                      index::IndexDataConsumer::ASTNodeInfo ASTNode) override {
    const SourceManager &SourceMgr = AST.getSourceManager();
    if (SourceMgr.getMainFileID() != FID ||
        std::find(Decls.begin(), Decls.end(), D) == Decls.end()) {
      return true;
    }
    SourceLocation End;
    const LangOptions &LangOpts = AST.getLangOpts();
    SourceLocation StartOfFileLoc = SourceMgr.getLocForStartOfFile(FID);
    SourceLocation HightlightStartLoc = StartOfFileLoc.getLocWithOffset(Offset);
    End =
        Lexer::getLocForEndOfToken(HightlightStartLoc, 0, SourceMgr, LangOpts);
    SourceRange SR(HightlightStartLoc, End);

    DocumentHighlightKind Kind = DocumentHighlightKind::Text;
    if (static_cast<index::SymbolRoleSet>(index::SymbolRole::Write) & Roles)
      Kind = DocumentHighlightKind::Write;
    else if (static_cast<index::SymbolRoleSet>(index::SymbolRole::Read) & Roles)
      Kind = DocumentHighlightKind::Read;

    DocumentHighlights.push_back(getDocumentHighlight(SR, Kind));
    return true;
  }

private:
  DocumentHighlight getDocumentHighlight(SourceRange SR,
                                         DocumentHighlightKind Kind) {
    const SourceManager &SourceMgr = AST.getSourceManager();
    SourceLocation LocStart = SR.getBegin();
    Position Begin;
    Begin.line = SourceMgr.getSpellingLineNumber(LocStart) - 1;
    Begin.character = SourceMgr.getSpellingColumnNumber(LocStart) - 1;
    Position End;
    End.line = SourceMgr.getSpellingLineNumber(SR.getEnd()) - 1;
    End.character = SourceMgr.getSpellingColumnNumber(SR.getEnd()) - 1;
    Range R = {Begin, End};
    DocumentHighlight DH;
    DH.range = R;
    DH.kind = Kind;
    return DH;
  }
};

} // namespace

llvm::Optional<Location>
getDeclarationLocation(ParsedAST &AST, const SourceRange &ValSourceRange) {
  const SourceManager &SourceMgr = AST.getASTContext().getSourceManager();
  const LangOptions &LangOpts = AST.getASTContext().getLangOpts();
  SourceLocation LocStart = ValSourceRange.getBegin();

  const FileEntry *F =
      SourceMgr.getFileEntryForID(SourceMgr.getFileID(LocStart));
  if (!F)
    return llvm::None;
  SourceLocation LocEnd = Lexer::getLocForEndOfToken(ValSourceRange.getEnd(), 0,
                                                     SourceMgr, LangOpts);
  Position Begin;
  Begin.line = SourceMgr.getSpellingLineNumber(LocStart) - 1;
  Begin.character = SourceMgr.getSpellingColumnNumber(LocStart) - 1;
  Position End;
  End.line = SourceMgr.getSpellingLineNumber(LocEnd) - 1;
  End.character = SourceMgr.getSpellingColumnNumber(LocEnd) - 1;
  Range R = {Begin, End};
  Location L;

  StringRef FilePath = F->tryGetRealPathName();
  if (FilePath.empty())
    FilePath = F->getName();
  L.uri = URI::fromFile(FilePath);
  L.range = R;
  return L;
}

std::vector<Location> clangd::findDefinitions(ParsedAST &AST, Position Pos,
                                              clangd::Logger &Logger) {
  const SourceManager &SourceMgr = AST.getASTContext().getSourceManager();
  const FileEntry *FE = SourceMgr.getFileEntryForID(SourceMgr.getMainFileID());
  if (!FE)
    return {};

  SourceLocation SourceLocationBeg = getBeginningOfIdentifier(AST, Pos, FE);

  auto DeclMacrosFinder = std::make_shared<DeclarationAndMacrosFinder>(
      llvm::errs(), SourceLocationBeg, AST.getASTContext(),
      AST.getPreprocessor());
  index::IndexingOptions IndexOpts;
  IndexOpts.SystemSymbolFilter =
      index::IndexingOptions::SystemSymbolFilterKind::All;
  IndexOpts.IndexFunctionLocals = true;

  indexTopLevelDecls(AST.getASTContext(), AST.getTopLevelDecls(),
                     DeclMacrosFinder, IndexOpts);

  std::vector<const Decl *> Decls = DeclMacrosFinder->takeDecls();
  std::vector<const MacroInfo *> MacroInfos =
      DeclMacrosFinder->takeMacroInfos();
  std::vector<Location> Result;

  for (auto Item : Decls) {
    auto L = getDeclarationLocation(AST, Item->getSourceRange());
    if (L)
      Result.push_back(*L);
  }

  for (auto Item : MacroInfos) {
    SourceRange SR(Item->getDefinitionLoc(), Item->getDefinitionEndLoc());
    auto L = getDeclarationLocation(AST, SR);
    if (L)
      Result.push_back(*L);
  }

  return Result;
}

std::vector<DocumentHighlight>
clangd::findDocumentHighlights(ParsedAST &AST, Position Pos,
                               clangd::Logger &Logger) {
  const SourceManager &SourceMgr = AST.getASTContext().getSourceManager();
  const FileEntry *FE = SourceMgr.getFileEntryForID(SourceMgr.getMainFileID());
  if (!FE)
    return {};

  SourceLocation SourceLocationBeg = getBeginningOfIdentifier(AST, Pos, FE);

  auto DeclMacrosFinder = std::make_shared<DeclarationAndMacrosFinder>(
      llvm::errs(), SourceLocationBeg, AST.getASTContext(),
      AST.getPreprocessor());
  index::IndexingOptions IndexOpts;
  IndexOpts.SystemSymbolFilter =
      index::IndexingOptions::SystemSymbolFilterKind::All;
  IndexOpts.IndexFunctionLocals = true;

  // Macro occurences are not currently handled.
  indexTopLevelDecls(AST.getASTContext(), AST.getTopLevelDecls(),
                     DeclMacrosFinder, IndexOpts);

  std::vector<const Decl *> SelectedDecls = DeclMacrosFinder->takeDecls();

  auto DocHighlightsFinder = std::make_shared<DocumentHighlightsFinder>(
      llvm::errs(), AST.getASTContext(), AST.getPreprocessor(), SelectedDecls);

  indexTopLevelDecls(AST.getASTContext(), AST.getTopLevelDecls(),
                     DocHighlightsFinder, IndexOpts);

  return DocHighlightsFinder->takeHighlights();
}

void ParsedAST::ensurePreambleDeclsDeserialized() {
  if (PreambleDeclsDeserialized || !Preamble)
    return;

  std::vector<const Decl *> Resolved;
  Resolved.reserve(Preamble->TopLevelDeclIDs.size());

  ExternalASTSource &Source = *getASTContext().getExternalSource();
  for (serialization::DeclID TopLevelDecl : Preamble->TopLevelDeclIDs) {
    // Resolve the declaration ID to an actual declaration, possibly
    // deserializing the declaration in the process.
    if (Decl *D = Source.GetExternalDecl(TopLevelDecl))
      Resolved.push_back(D);
  }

  TopLevelDecls.reserve(TopLevelDecls.size() +
                        Preamble->TopLevelDeclIDs.size());
  TopLevelDecls.insert(TopLevelDecls.begin(), Resolved.begin(), Resolved.end());

  PreambleDeclsDeserialized = true;
}

ParsedAST::ParsedAST(ParsedAST &&Other) = default;

ParsedAST &ParsedAST::operator=(ParsedAST &&Other) = default;

ParsedAST::~ParsedAST() {
  if (Action) {
    Action->EndSourceFile();
  }
}

ASTContext &ParsedAST::getASTContext() { return Clang->getASTContext(); }

const ASTContext &ParsedAST::getASTContext() const {
  return Clang->getASTContext();
}

Preprocessor &ParsedAST::getPreprocessor() { return Clang->getPreprocessor(); }

const Preprocessor &ParsedAST::getPreprocessor() const {
  return Clang->getPreprocessor();
}

ArrayRef<const Decl *> ParsedAST::getTopLevelDecls() {
  ensurePreambleDeclsDeserialized();
  return TopLevelDecls;
}

const std::vector<DiagWithFixIts> &ParsedAST::getDiagnostics() const {
  return Diags;
}

PreambleData::PreambleData(PrecompiledPreamble Preamble,
                           std::vector<serialization::DeclID> TopLevelDeclIDs,
                           std::vector<DiagWithFixIts> Diags)
    : Preamble(std::move(Preamble)),
      TopLevelDeclIDs(std::move(TopLevelDeclIDs)), Diags(std::move(Diags)) {}

ParsedAST::ParsedAST(std::shared_ptr<const PreambleData> Preamble,
                     std::unique_ptr<CompilerInstance> Clang,
                     std::unique_ptr<FrontendAction> Action,
                     std::vector<const Decl *> TopLevelDecls,
                     std::vector<DiagWithFixIts> Diags)
    : Preamble(std::move(Preamble)), Clang(std::move(Clang)),
      Action(std::move(Action)), Diags(std::move(Diags)),
      TopLevelDecls(std::move(TopLevelDecls)),
      PreambleDeclsDeserialized(false) {
  assert(this->Clang);
  assert(this->Action);
}

ParsedASTWrapper::ParsedASTWrapper(ParsedASTWrapper &&Wrapper)
    : AST(std::move(Wrapper.AST)) {}

ParsedASTWrapper::ParsedASTWrapper(llvm::Optional<ParsedAST> AST)
    : AST(std::move(AST)) {}

std::shared_ptr<CppFile>
CppFile::Create(PathRef FileName, tooling::CompileCommand Command,
                bool StorePreamblesInMemory,
                std::shared_ptr<PCHContainerOperations> PCHs,
                clangd::Logger &Logger) {
  return std::shared_ptr<CppFile>(new CppFile(FileName, std::move(Command),
                                              StorePreamblesInMemory,
                                              std::move(PCHs), Logger));
}

CppFile::CppFile(PathRef FileName, tooling::CompileCommand Command,
                 bool StorePreamblesInMemory,
                 std::shared_ptr<PCHContainerOperations> PCHs,
                 clangd::Logger &Logger)
    : FileName(FileName), Command(std::move(Command)),
      StorePreamblesInMemory(StorePreamblesInMemory), RebuildCounter(0),
      RebuildInProgress(false), PCHs(std::move(PCHs)), Logger(Logger) {
  Logger.log("Opened file " + FileName + " with command [" +
             this->Command.Directory + "] " +
             llvm::join(this->Command.CommandLine, " "));

  std::lock_guard<std::mutex> Lock(Mutex);
  LatestAvailablePreamble = nullptr;
  PreamblePromise.set_value(nullptr);
  PreambleFuture = PreamblePromise.get_future();

  ASTPromise.set_value(std::make_shared<ParsedASTWrapper>(llvm::None));
  ASTFuture = ASTPromise.get_future();
}

void CppFile::cancelRebuild() { deferCancelRebuild()(); }

UniqueFunction<void()> CppFile::deferCancelRebuild() {
  std::unique_lock<std::mutex> Lock(Mutex);
  // Cancel an ongoing rebuild, if any, and wait for it to finish.
  unsigned RequestRebuildCounter = ++this->RebuildCounter;
  // Rebuild asserts that futures aren't ready if rebuild is cancelled.
  // We want to keep this invariant.
  if (futureIsReady(PreambleFuture)) {
    PreamblePromise = std::promise<std::shared_ptr<const PreambleData>>();
    PreambleFuture = PreamblePromise.get_future();
  }
  if (futureIsReady(ASTFuture)) {
    ASTPromise = std::promise<std::shared_ptr<ParsedASTWrapper>>();
    ASTFuture = ASTPromise.get_future();
  }

  Lock.unlock();
  // Notify about changes to RebuildCounter.
  RebuildCond.notify_all();

  std::shared_ptr<CppFile> That = shared_from_this();
  return [That, RequestRebuildCounter]() {
    std::unique_lock<std::mutex> Lock(That->Mutex);
    CppFile *This = &*That;
    This->RebuildCond.wait(Lock, [This, RequestRebuildCounter]() {
      return !This->RebuildInProgress ||
             This->RebuildCounter != RequestRebuildCounter;
    });

    // This computation got cancelled itself, do nothing.
    if (This->RebuildCounter != RequestRebuildCounter)
      return;

    // Set empty results for Promises.
    That->PreamblePromise.set_value(nullptr);
    That->ASTPromise.set_value(std::make_shared<ParsedASTWrapper>(llvm::None));
  };
}

llvm::Optional<std::vector<DiagWithFixIts>>
CppFile::rebuild(StringRef NewContents,
                 IntrusiveRefCntPtr<vfs::FileSystem> VFS) {
  return deferRebuild(NewContents, std::move(VFS))();
}

UniqueFunction<llvm::Optional<std::vector<DiagWithFixIts>>()>
CppFile::deferRebuild(StringRef NewContents,
                      IntrusiveRefCntPtr<vfs::FileSystem> VFS) {
  std::shared_ptr<const PreambleData> OldPreamble;
  std::shared_ptr<PCHContainerOperations> PCHs;
  unsigned RequestRebuildCounter;
  {
    std::unique_lock<std::mutex> Lock(Mutex);
    // Increase RebuildCounter to cancel all ongoing FinishRebuild operations.
    // They will try to exit as early as possible and won't call set_value on
    // our promises.
    RequestRebuildCounter = ++this->RebuildCounter;
    PCHs = this->PCHs;

    // Remember the preamble to be used during rebuild.
    OldPreamble = this->LatestAvailablePreamble;
    // Setup std::promises and std::futures for Preamble and AST. Corresponding
    // futures will wait until the rebuild process is finished.
    if (futureIsReady(this->PreambleFuture)) {
      this->PreamblePromise =
          std::promise<std::shared_ptr<const PreambleData>>();
      this->PreambleFuture = this->PreamblePromise.get_future();
    }
    if (futureIsReady(this->ASTFuture)) {
      this->ASTPromise = std::promise<std::shared_ptr<ParsedASTWrapper>>();
      this->ASTFuture = this->ASTPromise.get_future();
    }
  } // unlock Mutex.
  // Notify about changes to RebuildCounter.
  RebuildCond.notify_all();

  // A helper to function to finish the rebuild. May be run on a different
  // thread.

  // Don't let this CppFile die before rebuild is finished.
  std::shared_ptr<CppFile> That = shared_from_this();
  auto FinishRebuild = [OldPreamble, VFS, RequestRebuildCounter, PCHs,
                        That](std::string NewContents) mutable // 'mutable' to
                                                               // allow changing
                                                               // OldPreamble.
      -> llvm::Optional<std::vector<DiagWithFixIts>> {
    // Only one execution of this method is possible at a time.
    // RebuildGuard will wait for any ongoing rebuilds to finish and will put us
    // into a state for doing a rebuild.
    RebuildGuard Rebuild(*That, RequestRebuildCounter);
    if (Rebuild.wasCancelledBeforeConstruction())
      return llvm::None;

    std::vector<const char *> ArgStrs;
    for (const auto &S : That->Command.CommandLine)
      ArgStrs.push_back(S.c_str());

    VFS->setCurrentWorkingDirectory(That->Command.Directory);

    std::unique_ptr<CompilerInvocation> CI;
    {
      // FIXME(ibiryukov): store diagnostics from CommandLine when we start
      // reporting them.
      IgnoreDiagnostics IgnoreDiagnostics;
      IntrusiveRefCntPtr<DiagnosticsEngine> CommandLineDiagsEngine =
          CompilerInstance::createDiagnostics(new DiagnosticOptions,
                                              &IgnoreDiagnostics, false);
      CI =
          createInvocationFromCommandLine(ArgStrs, CommandLineDiagsEngine, VFS);
      // createInvocationFromCommandLine sets DisableFree.
      CI->getFrontendOpts().DisableFree = false;
    }
    assert(CI && "Couldn't create CompilerInvocation");

    std::unique_ptr<llvm::MemoryBuffer> ContentsBuffer =
        llvm::MemoryBuffer::getMemBufferCopy(NewContents, That->FileName);

    // A helper function to rebuild the preamble or reuse the existing one. Does
    // not mutate any fields of CppFile, only does the actual computation.
    // Lamdba is marked mutable to call reset() on OldPreamble.
    auto DoRebuildPreamble =
        [&]() mutable -> std::shared_ptr<const PreambleData> {
      auto Bounds =
          ComputePreambleBounds(*CI->getLangOpts(), ContentsBuffer.get(), 0);
      if (OldPreamble && OldPreamble->Preamble.CanReuse(
                             *CI, ContentsBuffer.get(), Bounds, VFS.get())) {
        return OldPreamble;
      }
      // We won't need the OldPreamble anymore, release it so it can be deleted
      // (if there are no other references to it).
      OldPreamble.reset();

      trace::Span Tracer("Preamble");
      SPAN_ATTACH(Tracer, "File", That->FileName);
      std::vector<DiagWithFixIts> PreambleDiags;
      StoreDiagsConsumer PreambleDiagnosticsConsumer(/*ref*/ PreambleDiags);
      IntrusiveRefCntPtr<DiagnosticsEngine> PreambleDiagsEngine =
          CompilerInstance::createDiagnostics(
              &CI->getDiagnosticOpts(), &PreambleDiagnosticsConsumer, false);
      CppFilePreambleCallbacks SerializedDeclsCollector;
      auto BuiltPreamble = PrecompiledPreamble::Build(
          *CI, ContentsBuffer.get(), Bounds, *PreambleDiagsEngine, VFS, PCHs,
          /*StoreInMemory=*/That->StorePreamblesInMemory,
          SerializedDeclsCollector);

      if (BuiltPreamble) {
        return std::make_shared<PreambleData>(
            std::move(*BuiltPreamble),
            SerializedDeclsCollector.takeTopLevelDeclIDs(),
            std::move(PreambleDiags));
      } else {
        return nullptr;
      }
    };

    // Compute updated Preamble.
    std::shared_ptr<const PreambleData> NewPreamble = DoRebuildPreamble();
    // Publish the new Preamble.
    {
      std::lock_guard<std::mutex> Lock(That->Mutex);
      // We always set LatestAvailablePreamble to the new value, hoping that it
      // will still be usable in the further requests.
      That->LatestAvailablePreamble = NewPreamble;
      if (RequestRebuildCounter != That->RebuildCounter)
        return llvm::None; // Our rebuild request was cancelled, do nothing.
      That->PreamblePromise.set_value(NewPreamble);
    } // unlock Mutex

    // Prepare the Preamble and supplementary data for rebuilding AST.
    std::vector<DiagWithFixIts> Diagnostics;
    if (NewPreamble) {
      Diagnostics.insert(Diagnostics.begin(), NewPreamble->Diags.begin(),
                         NewPreamble->Diags.end());
    }

    // Compute updated AST.
    llvm::Optional<ParsedAST> NewAST;
    {
      trace::Span Tracer("Build");
      SPAN_ATTACH(Tracer, "File", That->FileName);
      NewAST =
          ParsedAST::Build(std::move(CI), std::move(NewPreamble),
                           std::move(ContentsBuffer), PCHs, VFS, That->Logger);
    }

    if (NewAST) {
      Diagnostics.insert(Diagnostics.end(), NewAST->getDiagnostics().begin(),
                         NewAST->getDiagnostics().end());
    } else {
      // Don't report even Preamble diagnostics if we coulnd't build AST.
      Diagnostics.clear();
    }

    // Publish the new AST.
    {
      std::lock_guard<std::mutex> Lock(That->Mutex);
      if (RequestRebuildCounter != That->RebuildCounter)
        return Diagnostics; // Our rebuild request was cancelled, don't set
                            // ASTPromise.

      That->ASTPromise.set_value(
          std::make_shared<ParsedASTWrapper>(std::move(NewAST)));
    } // unlock Mutex

    return Diagnostics;
  };

  return BindWithForward(FinishRebuild, NewContents.str());
}

std::shared_future<std::shared_ptr<const PreambleData>>
CppFile::getPreamble() const {
  std::lock_guard<std::mutex> Lock(Mutex);
  return PreambleFuture;
}

std::shared_ptr<const PreambleData> CppFile::getPossiblyStalePreamble() const {
  std::lock_guard<std::mutex> Lock(Mutex);
  return LatestAvailablePreamble;
}

std::shared_future<std::shared_ptr<ParsedASTWrapper>> CppFile::getAST() const {
  std::lock_guard<std::mutex> Lock(Mutex);
  return ASTFuture;
}

tooling::CompileCommand const &CppFile::getCompileCommand() const {
  return Command;
}

CppFile::RebuildGuard::RebuildGuard(CppFile &File,
                                    unsigned RequestRebuildCounter)
    : File(File), RequestRebuildCounter(RequestRebuildCounter) {
  std::unique_lock<std::mutex> Lock(File.Mutex);
  WasCancelledBeforeConstruction = File.RebuildCounter != RequestRebuildCounter;
  if (WasCancelledBeforeConstruction)
    return;

  File.RebuildCond.wait(Lock, [&File, RequestRebuildCounter]() {
    return !File.RebuildInProgress ||
           File.RebuildCounter != RequestRebuildCounter;
  });

  WasCancelledBeforeConstruction = File.RebuildCounter != RequestRebuildCounter;
  if (WasCancelledBeforeConstruction)
    return;

  File.RebuildInProgress = true;
}

bool CppFile::RebuildGuard::wasCancelledBeforeConstruction() const {
  return WasCancelledBeforeConstruction;
}

CppFile::RebuildGuard::~RebuildGuard() {
  if (WasCancelledBeforeConstruction)
    return;

  std::unique_lock<std::mutex> Lock(File.Mutex);
  assert(File.RebuildInProgress);
  File.RebuildInProgress = false;

  if (File.RebuildCounter == RequestRebuildCounter) {
    // Our rebuild request was successful.
    assert(futureIsReady(File.ASTFuture));
    assert(futureIsReady(File.PreambleFuture));
  } else {
    // Our rebuild request was cancelled, because further reparse was requested.
    assert(!futureIsReady(File.ASTFuture));
    assert(!futureIsReady(File.PreambleFuture));
  }

  Lock.unlock();
  File.RebuildCond.notify_all();
}

SourceLocation clangd::getBeginningOfIdentifier(ParsedAST &Unit,
                                                const Position &Pos,
                                                const FileEntry *FE) {
  // The language server protocol uses zero-based line and column numbers.
  // Clang uses one-based numbers.

  const ASTContext &AST = Unit.getASTContext();
  const SourceManager &SourceMgr = AST.getSourceManager();

  SourceLocation InputLocation =
      getMacroArgExpandedLocation(SourceMgr, FE, Pos);
  if (Pos.character == 0) {
    return InputLocation;
  }

  // This handle cases where the position is in the middle of a token or right
  // after the end of a token. In theory we could just use GetBeginningOfToken
  // to find the start of the token at the input position, but this doesn't
  // work when right after the end, i.e. foo|.
  // So try to go back by one and see if we're still inside the an identifier
  // token. If so, Take the beginning of this token.
  // (It should be the same identifier because you can't have two adjacent
  // identifiers without another token in between.)
  SourceLocation PeekBeforeLocation = getMacroArgExpandedLocation(
      SourceMgr, FE, Position{Pos.line, Pos.character - 1});
  Token Result;
  if (Lexer::getRawToken(PeekBeforeLocation, Result, SourceMgr,
                         AST.getLangOpts(), false)) {
    // getRawToken failed, just use InputLocation.
    return InputLocation;
  }

  if (Result.is(tok::raw_identifier)) {
    return Lexer::GetBeginningOfToken(PeekBeforeLocation, SourceMgr,
                                      AST.getLangOpts());
  }

  return InputLocation;
}