Index: clang-tools-extra/trunk/clangd/ClangdLSPServer.h
===================================================================
--- clang-tools-extra/trunk/clangd/ClangdLSPServer.h
+++ clang-tools-extra/trunk/clangd/ClangdLSPServer.h
@@ -82,6 +82,7 @@
   /// may be very expensive.  This method is normally called when the
   /// compilation database is changed.
   void reparseOpenedFiles();
+  void applyConfiguration(const ClangdConfigurationParamsChange &Settings);
 
   JSONOutput &Out;
   /// Used to indicate that the 'shutdown' request was received from the
Index: clang-tools-extra/trunk/clangd/ClangdLSPServer.cpp
===================================================================
--- clang-tools-extra/trunk/clangd/ClangdLSPServer.cpp
+++ clang-tools-extra/trunk/clangd/ClangdLSPServer.cpp
@@ -72,6 +72,9 @@
 } // namespace
 
 void ClangdLSPServer::onInitialize(InitializeParams &Params) {
+  if (Params.initializationOptions)
+    applyConfiguration(*Params.initializationOptions);
+
   if (Params.rootUri && *Params.rootUri)
     Server.setRootPath(Params.rootUri->file());
   else if (Params.rootPath && !Params.rootPath->empty())
@@ -398,11 +401,8 @@
                    });
 }
 
-// FIXME: This function needs to be properly tested.
-void ClangdLSPServer::onChangeConfiguration(
-    DidChangeConfigurationParams &Params) {
-  ClangdConfigurationParamsChange &Settings = Params.settings;
-
+void ClangdLSPServer::applyConfiguration(
+    const ClangdConfigurationParamsChange &Settings) {
   // Compilation database change.
   if (Settings.compilationDatabasePath.hasValue()) {
     NonCachedCDB.setCompileCommandsDir(
@@ -413,6 +413,12 @@
   }
 }
 
+// FIXME: This function needs to be properly tested.
+void ClangdLSPServer::onChangeConfiguration(
+    DidChangeConfigurationParams &Params) {
+  applyConfiguration(Params.settings);
+}
+
 ClangdLSPServer::ClangdLSPServer(JSONOutput &Out,
                                  const clangd::CodeCompleteOptions &CCOpts,
                                  llvm::Optional<Path> CompileCommandsDir,
Index: clang-tools-extra/trunk/clangd/Protocol.h
===================================================================
--- clang-tools-extra/trunk/clangd/Protocol.h
+++ clang-tools-extra/trunk/clangd/Protocol.h
@@ -322,6 +322,16 @@
 
 bool fromJSON(const llvm::json::Value &, ClientCapabilities &);
 
+/// Clangd extension to set clangd-specific "initializationOptions" in the
+/// "initialize" request and for the "workspace/didChangeConfiguration"
+/// notification since the data received is described as 'any' type in LSP.
+struct ClangdConfigurationParamsChange {
+  llvm::Optional<std::string> compilationDatabasePath;
+};
+bool fromJSON(const llvm::json::Value &, ClangdConfigurationParamsChange &);
+
+struct ClangdInitializationOptions : public ClangdConfigurationParamsChange {};
+
 struct InitializeParams {
   /// The process Id of the parent process that started
   /// the server. Is null if the process has not been started by another
@@ -348,6 +358,10 @@
 
   /// The initial trace setting. If omitted trace is disabled ('off').
   llvm::Optional<TraceLevel> trace;
+
+  // We use this predefined struct because it is easier to use
+  // than the protocol specified type of 'any'.
+  llvm::Optional<ClangdInitializationOptions> initializationOptions;
 };
 bool fromJSON(const llvm::json::Value &, InitializeParams &);
 
@@ -419,13 +433,6 @@
 };
 bool fromJSON(const llvm::json::Value &, DidChangeWatchedFilesParams &);
 
-/// Clangd extension to manage a workspace/didChangeConfiguration notification
-/// since the data received is described as 'any' type in LSP.
-struct ClangdConfigurationParamsChange {
-  llvm::Optional<std::string> compilationDatabasePath;
-};
-bool fromJSON(const llvm::json::Value &, ClangdConfigurationParamsChange &);
-
 struct DidChangeConfigurationParams {
   // We use this predefined struct because it is easier to use
   // than the protocol specified type of 'any'.
Index: clang-tools-extra/trunk/clangd/Protocol.cpp
===================================================================
--- clang-tools-extra/trunk/clangd/Protocol.cpp
+++ clang-tools-extra/trunk/clangd/Protocol.cpp
@@ -263,7 +263,7 @@
   O.map("rootPath", R.rootPath);
   O.map("capabilities", R.capabilities);
   O.map("trace", R.trace);
-  // initializationOptions, capabilities unused
+  O.map("initializationOptions", R.initializationOptions);
   return true;
 }