Index: clangd/ClangdServer.cpp
===================================================================
--- clangd/ClangdServer.cpp
+++ clangd/ClangdServer.cpp
@@ -531,9 +531,15 @@
   if (!C) // FIXME: Suppress diagnostics? Let the user know?
     C = CDB.getFallbackCommand(File);
 
+  // These flags are working for both gcc and clang-cl driver modes.
   // Inject the resource dir.
   // FIXME: Don't overwrite it if it's already there.
   C->CommandLine.push_back("-resource-dir=" + ResourceDir);
+  // Deprecations are often hidden for full-project build. They're useful in
+  // context.
+  C->CommandLine.push_back("-Wdeprecated");
+  // Adding -Wdeprecated would trigger errors in projects what set -Werror.
+  C->CommandLine.push_back("-Wno-error=deprecated");
   return std::move(*C);
 }
 
Index: unittests/clangd/ClangdTests.cpp
===================================================================
--- unittests/clangd/ClangdTests.cpp
+++ unittests/clangd/ClangdTests.cpp
@@ -963,6 +963,63 @@
                                        Field(&CodeCompletion::Name, "baz")));
 }
 
+TEST(ClangdCompilecommand, DiagnosticDeprecated) {
+  Annotations Test(R"cpp(
+    void foo() __attribute__(($foodeprecation[[deprecated]]));
+    class A {
+    public:
+      int x __attribute__(($xdeprecation[[deprecated]]));
+    };
+    int main() {
+      $foo[[foo]]();
+      return A().$x[[x]];
+    }
+  )cpp");
+  auto SourcePath = testPath("source/foo.cpp");
+
+  MockFSProvider FS;
+  struct DiagConsumer : public DiagnosticsConsumer {
+    void onDiagnosticsReady(PathRef File,
+                            std::vector<Diag> Diagnostics) override {
+      std::lock_guard<std::mutex> Lock(Mutex);
+      for(const Diag& D : Diagnostics) {
+        if(D.Category == "Deprecations") {
+          HadDeprecation = true;
+          if (D.Severity == DiagnosticsEngine::Error ||
+              D.Severity == DiagnosticsEngine::Fatal)
+            HadDeprecationAsError = true;
+        }
+      }
+    }
+
+    bool workedAsExpected() {
+      return !HadDeprecationAsError && HadDeprecation;
+    }
+
+    void reset() {
+      HadDeprecation = false;
+      HadDeprecationAsError = false;
+    }
+
+  private:
+    std::mutex Mutex;
+    bool HadDeprecationAsError = false;
+    bool HadDeprecation = false;
+  } DiagConsumer;
+  MockCompilationDatabase CDB;
+  CDB.ExtraClangFlags.push_back("-Wno-deprecated");
+  ClangdServer Server(CDB, FS, DiagConsumer, ClangdServer::optsForTest());
+
+  runAddDocument(Server, SourcePath, Test.code());
+  EXPECT_TRUE(DiagConsumer.workedAsExpected());
+  DiagConsumer.reset();
+
+  CDB.ExtraClangFlags.push_back("-Werror");
+  runAddDocument(Server, SourcePath, Test.code());
+  EXPECT_TRUE(DiagConsumer.workedAsExpected());
+}
+
+
 } // namespace
 } // namespace clangd
 } // namespace clang