--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/clang-tools-extra/clangd/FeatureModule.cpp	Tue Jun 15 19:15:29 2021 +0900
@@ -0,0 +1,37 @@
+//===--- FeatureModule.cpp - Plugging features into clangd ----------------===//
+//
+// 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 "FeatureModule.h"
+#include "support/Logger.h"
+
+namespace clang {
+namespace clangd {
+
+void FeatureModule::initialize(const Facilities &F) {
+  assert(!Fac.hasValue() && "Initialized twice");
+  Fac.emplace(F);
+}
+
+FeatureModule::Facilities &FeatureModule::facilities() {
+  assert(Fac.hasValue() && "Not initialized yet");
+  return *Fac;
+}
+
+bool FeatureModuleSet::addImpl(void *Key, std::unique_ptr<FeatureModule> M,
+                               const char *Source) {
+  if (!Map.try_emplace(Key, M.get()).second) {
+    // Source should (usually) include the name of the concrete module type.
+    elog("Tried to register duplicate feature modules via {0}", Source);
+    return false;
+  }
+  Modules.push_back(std::move(M));
+  return true;
+}
+
+} // namespace clangd
+} // namespace clang