//===- DependencyScanningWorker.cpp - clang-scan-deps worker --------------===//
//
// 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
//
//===----------------------------------------------------------------------===//

#include "clang/Tooling/DependencyScanning/DependencyScanningWorker.h"
#include "clang/Basic/DiagnosticDriver.h"
#include "clang/Basic/DiagnosticFrontend.h"
#include "clang/Basic/DiagnosticSerialization.h"
#include "clang/Driver/Compilation.h"
#include "clang/Driver/Driver.h"
#include "clang/Driver/Job.h"
#include "clang/Driver/Tool.h"
#include "clang/Frontend/CompilerInstance.h"
#include "clang/Frontend/CompilerInvocation.h"
#include "clang/Frontend/FrontendActions.h"
#include "clang/Frontend/TextDiagnosticPrinter.h"
#include "clang/Frontend/Utils.h"
#include "clang/Lex/PreprocessorOptions.h"
#include "clang/Serialization/ObjectFilePCHContainerReader.h"
#include "clang/Tooling/DependencyScanning/DependencyScanningService.h"
#include "clang/Tooling/DependencyScanning/InProcessModuleCache.h"
#include "clang/Tooling/DependencyScanning/ModuleDepCollector.h"
#include "llvm/ADT/IntrusiveRefCntPtr.h"
#include "llvm/Support/Allocator.h"
#include "llvm/Support/Error.h"
#include "llvm/Support/MemoryBuffer.h"
#include "llvm/TargetParser/Host.h"
#include <optional>

using namespace clang;
using namespace tooling;
using namespace dependencies;

namespace {

/// Forwards the gatherered dependencies to the consumer.
class DependencyConsumerForwarder : public DependencyFileGenerator {
public:
  DependencyConsumerForwarder(std::unique_ptr<DependencyOutputOptions> Opts,
                              StringRef WorkingDirectory, DependencyConsumer &C)
      : DependencyFileGenerator(*Opts), WorkingDirectory(WorkingDirectory),
        Opts(std::move(Opts)), C(C) {}

  void finishedMainFile(DiagnosticsEngine &Diags) override {
    C.handleDependencyOutputOpts(*Opts);
    llvm::SmallString<256> CanonPath;
    for (const auto &File : getDependencies()) {
      CanonPath = File;
      llvm::sys::path::remove_dots(CanonPath, /*remove_dot_dot=*/true);
      llvm::sys::fs::make_absolute(WorkingDirectory, CanonPath);
      C.handleFileDependency(CanonPath);
    }
  }

private:
  StringRef WorkingDirectory;
  std::unique_ptr<DependencyOutputOptions> Opts;
  DependencyConsumer &C;
};

static bool checkHeaderSearchPaths(const HeaderSearchOptions &HSOpts,
                                   const HeaderSearchOptions &ExistingHSOpts,
                                   DiagnosticsEngine *Diags,
                                   const LangOptions &LangOpts) {
  if (LangOpts.Modules) {
    if (HSOpts.VFSOverlayFiles != ExistingHSOpts.VFSOverlayFiles) {
      if (Diags) {
        Diags->Report(diag::warn_pch_vfsoverlay_mismatch);
        auto VFSNote = [&](int Type, ArrayRef<std::string> VFSOverlays) {
          if (VFSOverlays.empty()) {
            Diags->Report(diag::note_pch_vfsoverlay_empty) << Type;
          } else {
            std::string Files = llvm::join(VFSOverlays, "\n");
            Diags->Report(diag::note_pch_vfsoverlay_files) << Type << Files;
          }
        };
        VFSNote(0, HSOpts.VFSOverlayFiles);
        VFSNote(1, ExistingHSOpts.VFSOverlayFiles);
      }
    }
  }
  return false;
}

using PrebuiltModuleFilesT = decltype(HeaderSearchOptions::PrebuiltModuleFiles);

/// A listener that collects the imported modules and the input
/// files. While visiting, collect vfsoverlays and file inputs that determine
/// whether prebuilt modules fully resolve in stable directories.
class PrebuiltModuleListener : public ASTReaderListener {
public:
  PrebuiltModuleListener(PrebuiltModuleFilesT &PrebuiltModuleFiles,
                         llvm::SmallVector<std::string> &NewModuleFiles,
                         PrebuiltModulesAttrsMap &PrebuiltModulesASTMap,
                         const HeaderSearchOptions &HSOpts,
                         const LangOptions &LangOpts, DiagnosticsEngine &Diags,
                         const ArrayRef<StringRef> StableDirs)
      : PrebuiltModuleFiles(PrebuiltModuleFiles),
        NewModuleFiles(NewModuleFiles),
        PrebuiltModulesASTMap(PrebuiltModulesASTMap), ExistingHSOpts(HSOpts),
        ExistingLangOpts(LangOpts), Diags(Diags), StableDirs(StableDirs) {}

  bool needsImportVisitation() const override { return true; }
  bool needsInputFileVisitation() override { return true; }
  bool needsSystemInputFileVisitation() override { return true; }

  /// Accumulate the modules are transitively depended on by the initial
  /// prebuilt module.
  void visitImport(StringRef ModuleName, StringRef Filename) override {
    if (PrebuiltModuleFiles.insert({ModuleName.str(), Filename.str()}).second)
      NewModuleFiles.push_back(Filename.str());

    auto PrebuiltMapEntry = PrebuiltModulesASTMap.try_emplace(Filename);
    PrebuiltModuleASTAttrs &PrebuiltModule = PrebuiltMapEntry.first->second;
    if (PrebuiltMapEntry.second)
      PrebuiltModule.setInStableDir(!StableDirs.empty());

    if (auto It = PrebuiltModulesASTMap.find(CurrentFile);
        It != PrebuiltModulesASTMap.end() && CurrentFile != Filename)
      PrebuiltModule.addDependent(It->getKey());
  }

  /// For each input file discovered, check whether it's external path is in a
  /// stable directory. Traversal is stopped if the current module is not
  /// considered stable.
  bool visitInputFile(StringRef FilenameAsRequested, StringRef Filename,
                      bool isSystem, bool isOverridden,
                      bool isExplicitModule) override {
    if (StableDirs.empty())
      return false;
    auto PrebuiltEntryIt = PrebuiltModulesASTMap.find(CurrentFile);
    if ((PrebuiltEntryIt == PrebuiltModulesASTMap.end()) ||
        (!PrebuiltEntryIt->second.isInStableDir()))
      return false;

    PrebuiltEntryIt->second.setInStableDir(
        isPathInStableDir(StableDirs, Filename));
    return PrebuiltEntryIt->second.isInStableDir();
  }

  /// Update which module that is being actively traversed.
  void visitModuleFile(StringRef Filename,
                       serialization::ModuleKind Kind) override {
    // If the CurrentFile is not
    // considered stable, update any of it's transitive dependents.
    auto PrebuiltEntryIt = PrebuiltModulesASTMap.find(CurrentFile);
    if ((PrebuiltEntryIt != PrebuiltModulesASTMap.end()) &&
        !PrebuiltEntryIt->second.isInStableDir())
      PrebuiltEntryIt->second.updateDependentsNotInStableDirs(
          PrebuiltModulesASTMap);
    CurrentFile = Filename;
  }

  /// Check the header search options for a given module when considering
  /// if the module comes from stable directories.
  bool ReadHeaderSearchOptions(const HeaderSearchOptions &HSOpts,
                               StringRef ModuleFilename,
                               StringRef SpecificModuleCachePath,
                               bool Complain) override {

    auto PrebuiltMapEntry = PrebuiltModulesASTMap.try_emplace(CurrentFile);
    PrebuiltModuleASTAttrs &PrebuiltModule = PrebuiltMapEntry.first->second;
    if (PrebuiltMapEntry.second)
      PrebuiltModule.setInStableDir(!StableDirs.empty());

    if (PrebuiltModule.isInStableDir())
      PrebuiltModule.setInStableDir(areOptionsInStableDir(StableDirs, HSOpts));

    return false;
  }

  /// Accumulate vfsoverlays used to build these prebuilt modules.
  bool ReadHeaderSearchPaths(const HeaderSearchOptions &HSOpts,
                             bool Complain) override {

    auto PrebuiltMapEntry = PrebuiltModulesASTMap.try_emplace(CurrentFile);
    PrebuiltModuleASTAttrs &PrebuiltModule = PrebuiltMapEntry.first->second;
    if (PrebuiltMapEntry.second)
      PrebuiltModule.setInStableDir(!StableDirs.empty());

    PrebuiltModule.setVFS(
        llvm::StringSet<>(llvm::from_range, HSOpts.VFSOverlayFiles));

    return checkHeaderSearchPaths(
        HSOpts, ExistingHSOpts, Complain ? &Diags : nullptr, ExistingLangOpts);
  }

private:
  PrebuiltModuleFilesT &PrebuiltModuleFiles;
  llvm::SmallVector<std::string> &NewModuleFiles;
  PrebuiltModulesAttrsMap &PrebuiltModulesASTMap;
  const HeaderSearchOptions &ExistingHSOpts;
  const LangOptions &ExistingLangOpts;
  DiagnosticsEngine &Diags;
  std::string CurrentFile;
  const ArrayRef<StringRef> StableDirs;
};

/// Visit the given prebuilt module and collect all of the modules it
/// transitively imports and contributing input files.
static bool visitPrebuiltModule(StringRef PrebuiltModuleFilename,
                                CompilerInstance &CI,
                                PrebuiltModuleFilesT &ModuleFiles,
                                PrebuiltModulesAttrsMap &PrebuiltModulesASTMap,
                                DiagnosticsEngine &Diags,
                                const ArrayRef<StringRef> StableDirs) {
  // List of module files to be processed.
  llvm::SmallVector<std::string> Worklist;

  PrebuiltModuleListener Listener(ModuleFiles, Worklist, PrebuiltModulesASTMap,
                                  CI.getHeaderSearchOpts(), CI.getLangOpts(),
                                  Diags, StableDirs);

  Listener.visitModuleFile(PrebuiltModuleFilename,
                           serialization::MK_ExplicitModule);
  if (ASTReader::readASTFileControlBlock(
          PrebuiltModuleFilename, CI.getFileManager(), CI.getModuleCache(),
          CI.getPCHContainerReader(),
          /*FindModuleFileExtensions=*/false, Listener,
          /*ValidateDiagnosticOptions=*/false, ASTReader::ARR_OutOfDate))
    return true;

  while (!Worklist.empty()) {
    Listener.visitModuleFile(Worklist.back(), serialization::MK_ExplicitModule);
    if (ASTReader::readASTFileControlBlock(
            Worklist.pop_back_val(), CI.getFileManager(), CI.getModuleCache(),
            CI.getPCHContainerReader(),
            /*FindModuleFileExtensions=*/false, Listener,
            /*ValidateDiagnosticOptions=*/false))
      return true;
  }
  return false;
}

/// Transform arbitrary file name into an object-like file name.
static std::string makeObjFileName(StringRef FileName) {
  SmallString<128> ObjFileName(FileName);
  llvm::sys::path::replace_extension(ObjFileName, "o");
  return std::string(ObjFileName);
}

/// Deduce the dependency target based on the output file and input files.
static std::string
deduceDepTarget(const std::string &OutputFile,
                const SmallVectorImpl<FrontendInputFile> &InputFiles) {
  if (OutputFile != "-")
    return OutputFile;

  if (InputFiles.empty() || !InputFiles.front().isFile())
    return "clang-scan-deps\\ dependency";

  return makeObjFileName(InputFiles.front().getFile());
}

/// Sanitize diagnostic options for dependency scan.
static void sanitizeDiagOpts(DiagnosticOptions &DiagOpts) {
  // Don't print 'X warnings and Y errors generated'.
  DiagOpts.ShowCarets = false;
  // Don't write out diagnostic file.
  DiagOpts.DiagnosticSerializationFile.clear();
  // Don't emit warnings except for scanning specific warnings.
  // TODO: It would be useful to add a more principled way to ignore all
  //       warnings that come from source code. The issue is that we need to
  //       ignore warnings that could be surpressed by
  //       `#pragma clang diagnostic`, while still allowing some scanning
  //       warnings for things we're not ready to turn into errors yet.
  //       See `test/ClangScanDeps/diagnostic-pragmas.c` for an example.
  llvm::erase_if(DiagOpts.Warnings, [](StringRef Warning) {
    return llvm::StringSwitch<bool>(Warning)
        .Cases("pch-vfs-diff", "error=pch-vfs-diff", false)
        .StartsWith("no-error=", false)
        .Default(true);
  });
}

// Clang implements -D and -U by splatting text into a predefines buffer. This
// allows constructs such as `-DFඞ=3 "-D F\u{0D9E} 4 3 2”` to be accepted and
// define the same macro, or adding C++ style comments before the macro name.
//
// This function checks that the first non-space characters in the macro
// obviously form an identifier that can be uniqued on without lexing. Failing
// to do this could lead to changing the final definition of a macro.
//
// We could set up a preprocessor and actually lex the name, but that's very
// heavyweight for a situation that will almost never happen in practice.
static std::optional<StringRef> getSimpleMacroName(StringRef Macro) {
  StringRef Name = Macro.split("=").first.ltrim(" \t");
  std::size_t I = 0;

  auto FinishName = [&]() -> std::optional<StringRef> {
    StringRef SimpleName = Name.slice(0, I);
    if (SimpleName.empty())
      return std::nullopt;
    return SimpleName;
  };

  for (; I != Name.size(); ++I) {
    switch (Name[I]) {
    case '(': // Start of macro parameter list
    case ' ': // End of macro name
    case '\t':
      return FinishName();
    case '_':
      continue;
    default:
      if (llvm::isAlnum(Name[I]))
        continue;
      return std::nullopt;
    }
  }
  return FinishName();
}

static void canonicalizeDefines(PreprocessorOptions &PPOpts) {
  using MacroOpt = std::pair<StringRef, std::size_t>;
  std::vector<MacroOpt> SimpleNames;
  SimpleNames.reserve(PPOpts.Macros.size());
  std::size_t Index = 0;
  for (const auto &M : PPOpts.Macros) {
    auto SName = getSimpleMacroName(M.first);
    // Skip optimizing if we can't guarantee we can preserve relative order.
    if (!SName)
      return;
    SimpleNames.emplace_back(*SName, Index);
    ++Index;
  }

  llvm::stable_sort(SimpleNames, llvm::less_first());
  // Keep the last instance of each macro name by going in reverse
  auto NewEnd = std::unique(
      SimpleNames.rbegin(), SimpleNames.rend(),
      [](const MacroOpt &A, const MacroOpt &B) { return A.first == B.first; });
  SimpleNames.erase(SimpleNames.begin(), NewEnd.base());

  // Apply permutation.
  decltype(PPOpts.Macros) NewMacros;
  NewMacros.reserve(SimpleNames.size());
  for (std::size_t I = 0, E = SimpleNames.size(); I != E; ++I) {
    std::size_t OriginalIndex = SimpleNames[I].second;
    // We still emit undefines here as they may be undefining a predefined macro
    NewMacros.push_back(std::move(PPOpts.Macros[OriginalIndex]));
  }
  std::swap(PPOpts.Macros, NewMacros);
}

class ScanningDependencyDirectivesGetter : public DependencyDirectivesGetter {
  DependencyScanningWorkerFilesystem *DepFS;

public:
  ScanningDependencyDirectivesGetter(FileManager &FileMgr) : DepFS(nullptr) {
    FileMgr.getVirtualFileSystem().visit([&](llvm::vfs::FileSystem &FS) {
      auto *DFS = llvm::dyn_cast<DependencyScanningWorkerFilesystem>(&FS);
      if (DFS) {
        assert(!DepFS && "Found multiple scanning VFSs");
        DepFS = DFS;
      }
    });
    assert(DepFS && "Did not find scanning VFS");
  }

  std::unique_ptr<DependencyDirectivesGetter>
  cloneFor(FileManager &FileMgr) override {
    return std::make_unique<ScanningDependencyDirectivesGetter>(FileMgr);
  }

  std::optional<ArrayRef<dependency_directives_scan::Directive>>
  operator()(FileEntryRef File) override {
    return DepFS->getDirectiveTokens(File.getName());
  }
};

/// A clang tool that runs the preprocessor in a mode that's optimized for
/// dependency scanning for the given compiler invocation.
class DependencyScanningAction {
public:
  DependencyScanningAction(
      DependencyScanningService &Service, StringRef WorkingDirectory,
      DependencyConsumer &Consumer, DependencyActionController &Controller,
      llvm::IntrusiveRefCntPtr<DependencyScanningWorkerFilesystem> DepFS,
      std::optional<StringRef> ModuleName = std::nullopt)
      : Service(Service), WorkingDirectory(WorkingDirectory),
        Consumer(Consumer), Controller(Controller), DepFS(std::move(DepFS)),
        ModuleName(ModuleName) {}

  bool runInvocation(std::shared_ptr<CompilerInvocation> Invocation,
                     IntrusiveRefCntPtr<llvm::vfs::FileSystem> FS,
                     std::shared_ptr<PCHContainerOperations> PCHContainerOps,
                     DiagnosticConsumer *DiagConsumer) {
    // Make a deep copy of the original Clang invocation.
    CompilerInvocation OriginalInvocation(*Invocation);
    if (any(Service.getOptimizeArgs() & ScanningOptimizations::Macros))
      canonicalizeDefines(OriginalInvocation.getPreprocessorOpts());

    if (Scanned) {
      // Scanning runs once for the first -cc1 invocation in a chain of driver
      // jobs. For any dependent jobs, reuse the scanning result and just
      // update the LastCC1Arguments to correspond to the new invocation.
      // FIXME: to support multi-arch builds, each arch requires a separate scan
      setLastCC1Arguments(std::move(OriginalInvocation));
      return true;
    }

    Scanned = true;

    // Create a compiler instance to handle the actual work.
    auto ModCache = makeInProcessModuleCache(Service.getModuleCacheEntries());
    ScanInstanceStorage.emplace(std::move(Invocation),
                                std::move(PCHContainerOps), ModCache.get());
    CompilerInstance &ScanInstance = *ScanInstanceStorage;
    ScanInstance.setBuildingModule(false);

    // Create the compiler's actual diagnostics engine.
    sanitizeDiagOpts(ScanInstance.getDiagnosticOpts());
    assert(!DiagConsumerFinished && "attempt to reuse finished consumer");
    ScanInstance.createDiagnostics(*FS, DiagConsumer,
                                   /*ShouldOwnClient=*/false);
    if (!ScanInstance.hasDiagnostics())
      return false;

    ScanInstance.getPreprocessorOpts().AllowPCHWithDifferentModulesCachePath =
        true;

    if (ScanInstance.getHeaderSearchOpts().ModulesValidateOncePerBuildSession)
      ScanInstance.getHeaderSearchOpts().BuildSessionTimestamp =
          Service.getBuildSessionTimestamp();

    ScanInstance.getFrontendOpts().DisableFree = false;
    ScanInstance.getFrontendOpts().GenerateGlobalModuleIndex = false;
    ScanInstance.getFrontendOpts().UseGlobalModuleIndex = false;
    // This will prevent us compiling individual modules asynchronously since
    // FileManager is not thread-safe, but it does improve performance for now.
    ScanInstance.getFrontendOpts().ModulesShareFileManager = true;
    ScanInstance.getHeaderSearchOpts().ModuleFormat = "raw";
    ScanInstance.getHeaderSearchOpts().ModulesIncludeVFSUsage =
        any(Service.getOptimizeArgs() & ScanningOptimizations::VFS);

    // Support for virtual file system overlays.
    FS = createVFSFromCompilerInvocation(ScanInstance.getInvocation(),
                                         ScanInstance.getDiagnostics(),
                                         std::move(FS));

    // Create a new FileManager to match the invocation's FileSystemOptions.
    auto *FileMgr = ScanInstance.createFileManager(FS);

    // Use the dependency scanning optimized file system if requested to do so.
    if (DepFS) {
      StringRef ModulesCachePath =
          ScanInstance.getHeaderSearchOpts().ModuleCachePath;

      DepFS->resetBypassedPathPrefix();
      if (!ModulesCachePath.empty())
        DepFS->setBypassedPathPrefix(ModulesCachePath);

      ScanInstance.setDependencyDirectivesGetter(
          std::make_unique<ScanningDependencyDirectivesGetter>(*FileMgr));
    }

    ScanInstance.createSourceManager(*FileMgr);

    // Create a collection of stable directories derived from the ScanInstance
    // for determining whether module dependencies would fully resolve from
    // those directories.
    llvm::SmallVector<StringRef> StableDirs;
    const StringRef Sysroot = ScanInstance.getHeaderSearchOpts().Sysroot;
    if (!Sysroot.empty() &&
        (llvm::sys::path::root_directory(Sysroot) != Sysroot))
      StableDirs = {Sysroot, ScanInstance.getHeaderSearchOpts().ResourceDir};

    // Store a mapping of prebuilt module files and their properties like header
    // search options. This will prevent the implicit build to create duplicate
    // modules and will force reuse of the existing prebuilt module files
    // instead.
    PrebuiltModulesAttrsMap PrebuiltModulesASTMap;

    if (!ScanInstance.getPreprocessorOpts().ImplicitPCHInclude.empty())
      if (visitPrebuiltModule(
              ScanInstance.getPreprocessorOpts().ImplicitPCHInclude,
              ScanInstance,
              ScanInstance.getHeaderSearchOpts().PrebuiltModuleFiles,
              PrebuiltModulesASTMap, ScanInstance.getDiagnostics(), StableDirs))
        return false;

    // Create the dependency collector that will collect the produced
    // dependencies.
    //
    // This also moves the existing dependency output options from the
    // invocation to the collector. The options in the invocation are reset,
    // which ensures that the compiler won't create new dependency collectors,
    // and thus won't write out the extra '.d' files to disk.
    auto Opts = std::make_unique<DependencyOutputOptions>();
    std::swap(*Opts, ScanInstance.getInvocation().getDependencyOutputOpts());
    // We need at least one -MT equivalent for the generator of make dependency
    // files to work.
    if (Opts->Targets.empty())
      Opts->Targets = {
          deduceDepTarget(ScanInstance.getFrontendOpts().OutputFile,
                          ScanInstance.getFrontendOpts().Inputs)};
    Opts->IncludeSystemHeaders = true;

    switch (Service.getFormat()) {
    case ScanningOutputFormat::Make:
      ScanInstance.addDependencyCollector(
          std::make_shared<DependencyConsumerForwarder>(
              std::move(Opts), WorkingDirectory, Consumer));
      break;
    case ScanningOutputFormat::P1689:
    case ScanningOutputFormat::Full:
      MDC = std::make_shared<ModuleDepCollector>(
          Service, std::move(Opts), ScanInstance, Consumer, Controller,
          OriginalInvocation, std::move(PrebuiltModulesASTMap), StableDirs);
      ScanInstance.addDependencyCollector(MDC);
      break;
    }

    // Consider different header search and diagnostic options to create
    // different modules. This avoids the unsound aliasing of module PCMs.
    //
    // TODO: Implement diagnostic bucketing to reduce the impact of strict
    // context hashing.
    ScanInstance.getHeaderSearchOpts().ModulesStrictContextHash = true;
    ScanInstance.getHeaderSearchOpts().ModulesSerializeOnlyPreprocessor = true;
    ScanInstance.getHeaderSearchOpts().ModulesSkipDiagnosticOptions = true;
    ScanInstance.getHeaderSearchOpts().ModulesSkipHeaderSearchPaths = true;
    ScanInstance.getHeaderSearchOpts().ModulesSkipPragmaDiagnosticMappings =
        true;
    ScanInstance.getHeaderSearchOpts().ModulesForceValidateUserHeaders = false;

    // Avoid some checks and module map parsing when loading PCM files.
    ScanInstance.getPreprocessorOpts().ModulesCheckRelocated = false;

    std::unique_ptr<FrontendAction> Action;

    if (Service.getFormat() == ScanningOutputFormat::P1689)
      Action = std::make_unique<PreprocessOnlyAction>();
    else if (ModuleName)
      Action = std::make_unique<GetDependenciesByModuleNameAction>(*ModuleName);
    else
      Action = std::make_unique<ReadPCHAndPreprocessAction>();

    if (ScanInstance.getDiagnostics().hasErrorOccurred())
      return false;

    const bool Result = ScanInstance.ExecuteAction(*Action);

    // ExecuteAction is responsible for calling finish.
    DiagConsumerFinished = true;

    if (Result)
      setLastCC1Arguments(std::move(OriginalInvocation));

    return Result;
  }

  bool hasScanned() const { return Scanned; }
  bool hasDiagConsumerFinished() const { return DiagConsumerFinished; }

  /// Take the cc1 arguments corresponding to the most recent invocation used
  /// with this action. Any modifications implied by the discovered dependencies
  /// will have already been applied.
  std::vector<std::string> takeLastCC1Arguments() {
    std::vector<std::string> Result;
    std::swap(Result, LastCC1Arguments); // Reset LastCC1Arguments to empty.
    return Result;
  }

private:
  void setLastCC1Arguments(CompilerInvocation &&CI) {
    if (MDC)
      MDC->applyDiscoveredDependencies(CI);
    LastCC1Arguments = CI.getCC1CommandLine();
  }

  DependencyScanningService &Service;
  StringRef WorkingDirectory;
  DependencyConsumer &Consumer;
  DependencyActionController &Controller;
  llvm::IntrusiveRefCntPtr<DependencyScanningWorkerFilesystem> DepFS;
  std::optional<StringRef> ModuleName;
  std::optional<CompilerInstance> ScanInstanceStorage;
  std::shared_ptr<ModuleDepCollector> MDC;
  std::vector<std::string> LastCC1Arguments;
  bool Scanned = false;
  bool DiagConsumerFinished = false;
};

} // end anonymous namespace

DependencyScanningWorker::DependencyScanningWorker(
    DependencyScanningService &Service,
    llvm::IntrusiveRefCntPtr<llvm::vfs::FileSystem> FS)
    : Service(Service) {
  PCHContainerOps = std::make_shared<PCHContainerOperations>();
  // We need to read object files from PCH built outside the scanner.
  PCHContainerOps->registerReader(
      std::make_unique<ObjectFilePCHContainerReader>());
  // The scanner itself writes only raw ast files.
  PCHContainerOps->registerWriter(std::make_unique<RawPCHContainerWriter>());

  if (Service.shouldTraceVFS())
    FS = llvm::makeIntrusiveRefCnt<llvm::vfs::TracingFileSystem>(std::move(FS));

  switch (Service.getMode()) {
  case ScanningMode::DependencyDirectivesScan:
    DepFS =
        new DependencyScanningWorkerFilesystem(Service.getSharedCache(), FS);
    BaseFS = DepFS;
    break;
  case ScanningMode::CanonicalPreprocessing:
    DepFS = nullptr;
    BaseFS = FS;
    break;
  }
}

static std::unique_ptr<DiagnosticOptions>
createDiagOptions(const std::vector<std::string> &CommandLine) {
  std::vector<const char *> CLI;
  for (const std::string &Arg : CommandLine)
    CLI.push_back(Arg.c_str());
  auto DiagOpts = CreateAndPopulateDiagOpts(CLI);
  sanitizeDiagOpts(*DiagOpts);
  return DiagOpts;
}

llvm::Error DependencyScanningWorker::computeDependencies(
    StringRef WorkingDirectory, const std::vector<std::string> &CommandLine,
    DependencyConsumer &Consumer, DependencyActionController &Controller,
    std::optional<llvm::MemoryBufferRef> TUBuffer) {
  // Capture the emitted diagnostics and report them to the client
  // in the case of a failure.
  std::string DiagnosticOutput;
  llvm::raw_string_ostream DiagnosticsOS(DiagnosticOutput);
  auto DiagOpts = createDiagOptions(CommandLine);
  TextDiagnosticPrinter DiagPrinter(DiagnosticsOS, *DiagOpts);

  if (computeDependencies(WorkingDirectory, CommandLine, Consumer, Controller,
                          DiagPrinter, TUBuffer))
    return llvm::Error::success();
  return llvm::make_error<llvm::StringError>(DiagnosticsOS.str(),
                                             llvm::inconvertibleErrorCode());
}

llvm::Error DependencyScanningWorker::computeDependencies(
    StringRef WorkingDirectory, const std::vector<std::string> &CommandLine,
    DependencyConsumer &Consumer, DependencyActionController &Controller,
    StringRef ModuleName) {
  // Capture the emitted diagnostics and report them to the client
  // in the case of a failure.
  std::string DiagnosticOutput;
  llvm::raw_string_ostream DiagnosticsOS(DiagnosticOutput);
  auto DiagOpts = createDiagOptions(CommandLine);
  TextDiagnosticPrinter DiagPrinter(DiagnosticsOS, *DiagOpts);

  if (computeDependencies(WorkingDirectory, CommandLine, Consumer, Controller,
                          DiagPrinter, ModuleName))
    return llvm::Error::success();
  return llvm::make_error<llvm::StringError>(DiagnosticsOS.str(),
                                             llvm::inconvertibleErrorCode());
}

static bool forEachDriverJob(
    ArrayRef<std::string> ArgStrs, DiagnosticsEngine &Diags,
    IntrusiveRefCntPtr<llvm::vfs::FileSystem> FS,
    llvm::function_ref<bool(const driver::Command &Cmd)> Callback) {
  SmallVector<const char *, 256> Argv;
  Argv.reserve(ArgStrs.size());
  for (const std::string &Arg : ArgStrs)
    Argv.push_back(Arg.c_str());

  std::unique_ptr<driver::Driver> Driver = std::make_unique<driver::Driver>(
      Argv[0], llvm::sys::getDefaultTargetTriple(), Diags,
      "clang LLVM compiler", FS);
  Driver->setTitle("clang_based_tool");

  llvm::BumpPtrAllocator Alloc;
  bool CLMode = driver::IsClangCL(
      driver::getDriverMode(Argv[0], ArrayRef(Argv).slice(1)));

  if (llvm::Error E =
          driver::expandResponseFiles(Argv, CLMode, Alloc, FS.get())) {
    Diags.Report(diag::err_drv_expand_response_file)
        << llvm::toString(std::move(E));
    return false;
  }

  const std::unique_ptr<driver::Compilation> Compilation(
      Driver->BuildCompilation(llvm::ArrayRef(Argv)));
  if (!Compilation)
    return false;

  if (Compilation->containsError())
    return false;

  for (const driver::Command &Job : Compilation->getJobs()) {
    if (!Callback(Job))
      return false;
  }
  return true;
}

static bool createAndRunToolInvocation(
    std::vector<std::string> CommandLine, DependencyScanningAction &Action,
    IntrusiveRefCntPtr<llvm::vfs::FileSystem> FS,
    std::shared_ptr<clang::PCHContainerOperations> &PCHContainerOps,
    DiagnosticsEngine &Diags, DependencyConsumer &Consumer) {

  // Save executable path before providing CommandLine to ToolInvocation
  std::string Executable = CommandLine[0];

  llvm::opt::ArgStringList Argv;
  for (const std::string &Str : ArrayRef(CommandLine).drop_front())
    Argv.push_back(Str.c_str());

  auto Invocation = std::make_shared<CompilerInvocation>();
  if (!CompilerInvocation::CreateFromArgs(*Invocation, Argv, Diags)) {
    // FIXME: Should we just go on like cc1_main does?
    return false;
  }

  if (!Action.runInvocation(std::move(Invocation), std::move(FS),
                            PCHContainerOps, Diags.getClient()))
    return false;

  std::vector<std::string> Args = Action.takeLastCC1Arguments();
  Consumer.handleBuildCommand({std::move(Executable), std::move(Args)});
  return true;
}

bool DependencyScanningWorker::scanDependencies(
    StringRef WorkingDirectory, const std::vector<std::string> &CommandLine,
    DependencyConsumer &Consumer, DependencyActionController &Controller,
    DiagnosticConsumer &DC, llvm::IntrusiveRefCntPtr<llvm::vfs::FileSystem> FS,
    std::optional<StringRef> ModuleName) {
  std::vector<const char *> CCommandLine(CommandLine.size(), nullptr);
  llvm::transform(CommandLine, CCommandLine.begin(),
                  [](const std::string &Str) { return Str.c_str(); });
  auto DiagOpts = CreateAndPopulateDiagOpts(CCommandLine);
  sanitizeDiagOpts(*DiagOpts);
  auto Diags = CompilerInstance::createDiagnostics(*FS, *DiagOpts, &DC,
                                                   /*ShouldOwnClient=*/false);

  DependencyScanningAction Action(Service, WorkingDirectory, Consumer,
                                  Controller, DepFS, ModuleName);

  bool Success = false;
  if (CommandLine[1] == "-cc1") {
    Success = createAndRunToolInvocation(CommandLine, Action, FS,
                                         PCHContainerOps, *Diags, Consumer);
  } else {
    Success = forEachDriverJob(
        CommandLine, *Diags, FS, [&](const driver::Command &Cmd) {
          if (StringRef(Cmd.getCreator().getName()) != "clang") {
            // Non-clang command. Just pass through to the dependency
            // consumer.
            Consumer.handleBuildCommand(
                {Cmd.getExecutable(),
                 {Cmd.getArguments().begin(), Cmd.getArguments().end()}});
            return true;
          }

          // Insert -cc1 comand line options into Argv
          std::vector<std::string> Argv;
          Argv.push_back(Cmd.getExecutable());
          llvm::append_range(Argv, Cmd.getArguments());

          // Create an invocation that uses the underlying file
          // system to ensure that any file system requests that
          // are made by the driver do not go through the
          // dependency scanning filesystem.
          return createAndRunToolInvocation(std::move(Argv), Action, FS,
                                            PCHContainerOps, *Diags, Consumer);
        });
  }

  if (Success && !Action.hasScanned())
    Diags->Report(diag::err_fe_expected_compiler_job)
        << llvm::join(CommandLine, " ");

  // Ensure finish() is called even if we never reached ExecuteAction().
  if (!Action.hasDiagConsumerFinished())
    DC.finish();

  return Success && Action.hasScanned();
}

bool DependencyScanningWorker::computeDependencies(
    StringRef WorkingDirectory, const std::vector<std::string> &CommandLine,
    DependencyConsumer &Consumer, DependencyActionController &Controller,
    DiagnosticConsumer &DC, std::optional<llvm::MemoryBufferRef> TUBuffer) {
  // Reset what might have been modified in the previous worker invocation.
  BaseFS->setCurrentWorkingDirectory(WorkingDirectory);

  std::optional<std::vector<std::string>> ModifiedCommandLine;
  llvm::IntrusiveRefCntPtr<llvm::vfs::FileSystem> ModifiedFS;

  // If we're scanning based on a module name alone, we don't expect the client
  // to provide us with an input file. However, the driver really wants to have
  // one. Let's just make it up to make the driver happy.
  if (TUBuffer) {
    auto OverlayFS =
        llvm::makeIntrusiveRefCnt<llvm::vfs::OverlayFileSystem>(BaseFS);
    auto InMemoryFS =
        llvm::makeIntrusiveRefCnt<llvm::vfs::InMemoryFileSystem>();
    InMemoryFS->setCurrentWorkingDirectory(WorkingDirectory);
    auto InputPath = TUBuffer->getBufferIdentifier();
    InMemoryFS->addFile(
        InputPath, 0,
        llvm::MemoryBuffer::getMemBufferCopy(TUBuffer->getBuffer()));
    llvm::IntrusiveRefCntPtr<llvm::vfs::FileSystem> InMemoryOverlay =
        InMemoryFS;

    OverlayFS->pushOverlay(InMemoryOverlay);
    ModifiedFS = OverlayFS;
    ModifiedCommandLine = CommandLine;
    ModifiedCommandLine->emplace_back(InputPath);
  }

  const std::vector<std::string> &FinalCommandLine =
      ModifiedCommandLine ? *ModifiedCommandLine : CommandLine;
  auto &FinalFS = ModifiedFS ? ModifiedFS : BaseFS;

  return scanDependencies(WorkingDirectory, FinalCommandLine, Consumer,
                          Controller, DC, FinalFS, /*ModuleName=*/std::nullopt);
}

bool DependencyScanningWorker::computeDependencies(
    StringRef WorkingDirectory, const std::vector<std::string> &CommandLine,
    DependencyConsumer &Consumer, DependencyActionController &Controller,
    DiagnosticConsumer &DC, StringRef ModuleName) {
  // Reset what might have been modified in the previous worker invocation.
  BaseFS->setCurrentWorkingDirectory(WorkingDirectory);

  // If we're scanning based on a module name alone, we don't expect the client
  // to provide us with an input file. However, the driver really wants to have
  // one. Let's just make it up to make the driver happy.
  auto OverlayFS =
      llvm::makeIntrusiveRefCnt<llvm::vfs::OverlayFileSystem>(BaseFS);
  auto InMemoryFS = llvm::makeIntrusiveRefCnt<llvm::vfs::InMemoryFileSystem>();
  InMemoryFS->setCurrentWorkingDirectory(WorkingDirectory);
  SmallString<128> FakeInputPath;
  // TODO: We should retry the creation if the path already exists.
  llvm::sys::fs::createUniquePath(ModuleName + "-%%%%%%%%.input", FakeInputPath,
                                  /*MakeAbsolute=*/false);
  InMemoryFS->addFile(FakeInputPath, 0, llvm::MemoryBuffer::getMemBuffer(""));
  llvm::IntrusiveRefCntPtr<llvm::vfs::FileSystem> InMemoryOverlay = InMemoryFS;

  OverlayFS->pushOverlay(InMemoryOverlay);
  auto ModifiedCommandLine = CommandLine;
  ModifiedCommandLine.emplace_back(FakeInputPath);

  return scanDependencies(WorkingDirectory, ModifiedCommandLine, Consumer,
                          Controller, DC, OverlayFS, ModuleName);
}

DependencyActionController::~DependencyActionController() {}