--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/include/llvm/Support/FileCollector.h	Wed Aug 14 16:55:33 2019 +0900
@@ -0,0 +1,79 @@
+//===-- FileCollector.h -----------------------------------------*- 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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_SUPPORT_FILE_COLLECTOR_H
+#define LLVM_SUPPORT_FILE_COLLECTOR_H
+
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/ADT/StringMap.h"
+#include "llvm/ADT/StringSet.h"
+#include "llvm/ADT/Twine.h"
+#include "llvm/Support/VirtualFileSystem.h"
+
+#include <mutex>
+
+namespace llvm {
+
+/// Collects files into a directory and generates a mapping that can be used by
+/// the VFS.
+class FileCollector {
+public:
+  FileCollector(std::string Root, std::string OverlayRoot);
+
+  void addFile(const Twine &file);
+
+  /// Write the yaml mapping (for the VFS) to the given file.
+  std::error_code writeMapping(StringRef mapping_file);
+
+  /// Copy the files into the root directory.
+  ///
+  /// When StopOnError is true (the default) we abort as soon as one file
+  /// cannot be copied. This is relatively common, for example when a file was
+  /// removed after it was added to the mapping.
+  std::error_code copyFiles(bool StopOnError = true);
+
+  /// Create a VFS that collects all the paths that might be looked at by the
+  /// file system accesses.
+  static IntrusiveRefCntPtr<vfs::FileSystem>
+  createCollectorVFS(IntrusiveRefCntPtr<vfs::FileSystem> BaseFS,
+                     std::shared_ptr<FileCollector> Collector);
+
+private:
+  void addFileImpl(StringRef SrcPath);
+
+  bool markAsSeen(StringRef Path) { return Seen.insert(Path).second; }
+
+  bool getRealPath(StringRef SrcPath, SmallVectorImpl<char> &Result);
+
+  void addFileToMapping(StringRef VirtualPath, StringRef RealPath) {
+    VFSWriter.addFileMapping(VirtualPath, RealPath);
+  }
+
+protected:
+  /// Synchronizes adding files.
+  std::mutex Mutex;
+
+  /// The root directory where files are copied.
+  std::string Root;
+
+  /// The root directory where the VFS overlay lives.
+  std::string OverlayRoot;
+
+  /// Tracks already seen files so they can be skipped.
+  StringSet<> Seen;
+
+  /// The yaml mapping writer.
+  vfs::YAMLVFSWriter VFSWriter;
+
+  /// Caches RealPath calls when resolving symlinks.
+  StringMap<std::string> SymlinkMap;
+};
+
+} // end namespace llvm
+
+#endif // LLVM_SUPPORT_FILE_COLLECTOR_H