Index: clangd/ClangdLSPServer.cpp
===================================================================
--- clangd/ClangdLSPServer.cpp
+++ clangd/ClangdLSPServer.cpp
@@ -149,9 +149,13 @@
   if (Params.contentChanges.size() != 1)
     return replyError(ErrorCode::InvalidParams,
                       "can only apply one change at a time");
+  auto WantDiags = WantDiagnostics::Auto;
+  if (Params.wantDiagnostics.hasValue())
+    WantDiags = Params.wantDiagnostics.getValue() ? WantDiagnostics::Yes
+                                                  : WantDiagnostics::No;
   // We only support full syncing right now.
   Server.addDocument(Params.textDocument.uri.file(),
-                     Params.contentChanges[0].text, WantDiagnostics::Auto);
+                     Params.contentChanges[0].text, WantDiags);
 }
 
 void ClangdLSPServer::onFileEvent(DidChangeWatchedFilesParams &Params) {
Index: clangd/Protocol.h
===================================================================
--- clangd/Protocol.h
+++ clangd/Protocol.h
@@ -297,6 +297,12 @@
 
   /// The actual content changes.
   std::vector<TextDocumentContentChangeEvent> contentChanges;
+
+  /// Forces diagnostics to be generated, or to not be generated, for this
+  /// version of the file. If not set, diagnostics are eventually consistent:
+  /// either they will be provided for this version or some subsequent one.
+  /// This is a clangd extension.
+  llvm::Optional<bool> wantDiagnostics;
 };
 bool fromJSON(const json::Expr &, DidChangeTextDocumentParams &);
 
Index: clangd/Protocol.cpp
===================================================================
--- clangd/Protocol.cpp
+++ clangd/Protocol.cpp
@@ -221,7 +221,8 @@
 bool fromJSON(const json::Expr &Params, DidChangeTextDocumentParams &R) {
   json::ObjectMapper O(Params);
   return O && O.map("textDocument", R.textDocument) &&
-         O.map("contentChanges", R.contentChanges);
+         O.map("contentChanges", R.contentChanges) &&
+         O.map("wantDiagnostics", R.wantDiagnostics);
 }
 
 bool fromJSON(const json::Expr &E, FileChangeType &Out) {