--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/clang-tools-extra/clangd/support/FSProvider.h	Mon May 25 11:55:54 2020 +0900
@@ -0,0 +1,40 @@
+//===--- FSProvider.h - VFS provider for ClangdServer ------------*- 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_CLANG_TOOLS_EXTRA_CLANGD_SUPPORT_FSPROVIDER_H
+#define LLVM_CLANG_TOOLS_EXTRA_CLANGD_SUPPORT_FSPROVIDER_H
+
+#include "llvm/ADT/IntrusiveRefCntPtr.h"
+#include "llvm/Support/VirtualFileSystem.h"
+
+namespace clang {
+namespace clangd {
+
+// Wrapper for vfs::FileSystem for use in multithreaded programs like clangd.
+// As FileSystem is not threadsafe, concurrent threads must each obtain one.
+class FileSystemProvider {
+public:
+  virtual ~FileSystemProvider() = default;
+  /// Called by ClangdServer to obtain a vfs::FileSystem to be used for parsing.
+  /// Context::current() will be the context passed to the clang entrypoint,
+  /// such as addDocument(), and will also be propagated to result callbacks.
+  /// Embedders may use this to isolate filesystem accesses.
+  virtual llvm::IntrusiveRefCntPtr<llvm::vfs::FileSystem>
+  getFileSystem() const = 0;
+};
+
+class RealFileSystemProvider : public FileSystemProvider {
+public:
+  llvm::IntrusiveRefCntPtr<llvm::vfs::FileSystem>
+  getFileSystem() const override;
+};
+
+} // namespace clangd
+} // namespace clang
+
+#endif