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 +297,15 @@
 
   /// The actual content changes.
   std::vector<TextDocumentContentChangeEvent> contentChanges;
+
+  /// If this is not set, diagnostics will be generated for the current version
+  /// or a subsequent one.
+  /// If this is set to true, dianostics are guaranteed to be generated for the
+  /// current version.
+  /// If this is set to false, dianostics will not be generated for this
+  /// request.
+  /// 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) {
Index: test/clangd/want-diagnostics.test
===================================================================
--- /dev/null
+++ test/clangd/want-diagnostics.test
@@ -0,0 +1,19 @@
+# RUN: clangd -lit-test < %s | FileCheck -strict-whitespace %s
+{"jsonrpc":"2.0","id":0,"method":"initialize","params":{"processId":123,"rootPath":"clangd","capabilities":{},"trace":"off"}}
+---
+{"jsonrpc":"2.0","method":"textDocument/didOpen","params":{"textDocument":{"uri":"test:///main.cpp","languageId":"cpp","version":1,"text":"void main() {}"}}}
+#      CHECK:  "method": "textDocument/publishDiagnostics",
+---
+{"jsonrpc":"2.0","method":"textDocument/didChange","params":{"textDocument":{"uri":"test:///main.cpp","version":2},"contentChanges":[{"text":"void main() {}"}]}}
+---
+#      CHECK:  "method": "textDocument/publishDiagnostics",
+{"jsonrpc":"2.0","method":"textDocument/didChange","params":{"textDocument":{"uri":"test:///main.cpp","version":3},"contentChanges":[{"text":"void main() {}"}],"wantDiagnostics":true}}
+---
+#      CHECK:  "method": "textDocument/publishDiagnostics",
+{"jsonrpc":"2.0","method":"textDocument/didChange","params":{"textDocument":{"uri":"test:///main.cpp","version":4},"contentChanges":[{"text":"void main() {}"}],"wantDiagnostics":false}}
+---
+#      CHECK-NOT:  "method": "textDocument/publishDiagnostics",
+{"jsonrpc":"2.0","id":2,"method":"shutdown"}
+#      CHECK:  "method": "textDocument/publishDiagnostics",
+---
+{"jsonrpc":"2.0","method":"exit"}