text: //===- FileSystemStatCache.cpp - Caching for 'stat' calls -----------------===//
  //
  // 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
  //
  //===----------------------------------------------------------------------===//
  //
  //  This file defines the FileSystemStatCache interface.
  //
  //===----------------------------------------------------------------------===//
  
  #include "clang/Basic/FileSystemStatCache.h"
  #include "llvm/Support/Chrono.h"
  #include "llvm/Support/ErrorOr.h"
  #include "llvm/Support/Path.h"
  #include "llvm/Support/VirtualFileSystem.h"
  #include <utility>
  
  using namespace clang;
  
  void FileSystemStatCache::anchor() {}
  
  static void copyStatusToFileData(const llvm::vfs::Status &Status,
                                   FileData &Data) {
    Data.Name = Status.getName();
    Data.Size = Status.getSize();
    Data.ModTime = llvm::sys::toTimeT(Status.getLastModificationTime());
    Data.UniqueID = Status.getUniqueID();
    Data.IsDirectory = Status.isDirectory();
    Data.IsNamedPipe = Status.getType() == llvm::sys::fs::file_type::fifo_file;
    Data.InPCH = false;
    Data.IsVFSMapped = Status.IsVFSMapped;
  }
  
  /// FileSystemStatCache::get - Get the 'stat' information for the specified
  /// path, using the cache to accelerate it if possible.  This returns true if
  /// the path does not exist or false if it exists.
  ///
  /// If isFile is true, then this lookup should only return success for files
  /// (not directories).  If it is false this lookup should only return
  /// success for directories (not files).  On a successful file lookup, the
  /// implementation can optionally fill in FileDescriptor with a valid
  /// descriptor and the client guarantees that it will close it.
  bool FileSystemStatCache::get(StringRef Path, FileData &Data, bool isFile,
                                std::unique_ptr<llvm::vfs::File> *F,
                                FileSystemStatCache *Cache,
                                llvm::vfs::FileSystem &FS) {
    LookupResult R;
    bool isForDir = !isFile;
  
    // If we have a cache, use it to resolve the stat query.
    if (Cache)
      R = Cache->getStat(Path, Data, isFile, F, FS);
    else if (isForDir || !F) {
      // If this is a directory or a file descriptor is not needed and we have
      // no cache, just go to the file system.
      llvm::ErrorOr<llvm::vfs::Status> Status = FS.status(Path);
      if (!Status) {
        R = CacheMissing;
      } else {
        R = CacheExists;
        copyStatusToFileData(*Status, Data);
      }
    } else {
      // Otherwise, we have to go to the filesystem.  We can always just use
      // 'stat' here, but (for files) the client is asking whether the file exists
      // because it wants to turn around and *open* it.  It is more efficient to
      // do "open+fstat" on success than it is to do "stat+open".
      //
      // Because of this, check to see if the file exists with 'open'.  If the
      // open succeeds, use fstat to get the stat info.
      auto OwnedFile = FS.openFileForRead(Path);
  
      if (!OwnedFile) {
        // If the open fails, our "stat" fails.
        R = CacheMissing;
      } else {
        // Otherwise, the open succeeded.  Do an fstat to get the information
        // about the file.  We'll end up returning the open file descriptor to the
        // client to do what they please with it.
        llvm::ErrorOr<llvm::vfs::Status> Status = (*OwnedFile)->status();
        if (Status) {
          R = CacheExists;
          copyStatusToFileData(*Status, Data);
          *F = std::move(*OwnedFile);
        } else {
          // fstat rarely fails.  If it does, claim the initial open didn't
          // succeed.
          R = CacheMissing;
          *F = nullptr;
        }
      }
    }
  
    // If the path doesn't exist, return failure.
    if (R == CacheMissing) return true;
  
    // If the path exists, make sure that its "directoryness" matches the clients
    // demands.
    if (Data.IsDirectory != isForDir) {
      // If not, close the file if opened.
      if (F)
        *F = nullptr;
  
      return true;
    }
  
    return false;
  }
  
  MemorizeStatCalls::LookupResult
  MemorizeStatCalls::getStat(StringRef Path, FileData &Data, bool isFile,
                             std::unique_ptr<llvm::vfs::File> *F,
                             llvm::vfs::FileSystem &FS) {
    if (get(Path, Data, isFile, F, nullptr, FS)) {
      // Do not cache failed stats, it is easy to construct common inconsistent
      // situations if we do, and they are not important for PCH performance
      // (which currently only needs the stats to construct the initial
      // FileManager entries).
      return CacheMissing;
    }
  
    // Cache file 'stat' results and directories with absolutely paths.
    if (!Data.IsDirectory || llvm::sys::path::is_absolute(Path))
      StatCalls[Path] = Data;
  
    return CacheExists;
  }
  