--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/clang-tools-extra/clangd/DraftStore.h	Thu Feb 13 15:10:13 2020 +0900
@@ -0,0 +1,59 @@
+//===--- DraftStore.h - File contents container -----------------*- 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_DRAFTSTORE_H
+#define LLVM_CLANG_TOOLS_EXTRA_CLANGD_DRAFTSTORE_H
+
+#include "Path.h"
+#include "Protocol.h"
+#include "clang/Basic/LLVM.h"
+#include "llvm/ADT/StringMap.h"
+#include <mutex>
+#include <string>
+#include <vector>
+
+namespace clang {
+namespace clangd {
+
+/// A thread-safe container for files opened in a workspace, addressed by
+/// filenames. The contents are owned by the DraftStore. This class supports
+/// both whole and incremental updates of the documents.
+class DraftStore {
+public:
+  /// \return Contents of the stored document.
+  /// For untracked files, a llvm::None is returned.
+  llvm::Optional<std::string> getDraft(PathRef File) const;
+
+  /// \return List of names of the drafts in this store.
+  std::vector<Path> getActiveFiles() const;
+
+  /// Replace contents of the draft for \p File with \p Contents.
+  void addDraft(PathRef File, StringRef Contents);
+
+  /// Update the contents of the draft for \p File based on \p Changes.
+  /// If a position in \p Changes is invalid (e.g. out-of-range), the
+  /// draft is not modified.
+  ///
+  /// \return The new version of the draft for \p File, or an error if the
+  /// changes couldn't be applied.
+  llvm::Expected<std::string>
+  updateDraft(PathRef File,
+              llvm::ArrayRef<TextDocumentContentChangeEvent> Changes);
+
+  /// Remove the draft from the store.
+  void removeDraft(PathRef File);
+
+private:
+  mutable std::mutex Mutex;
+  llvm::StringMap<std::string> Drafts;
+};
+
+} // namespace clangd
+} // namespace clang
+
+#endif