[clangd] Track tweaks that fail the apply stage

clang-tools-extra/clangd/ClangdServer.cpp

void ClangdServer::enumerateTweaks(PathRef File, Range Sel,
   };
 
   WorkScheduler.runWithAST("EnumerateTweaks", File, std::move(Action),
                            TUScheduler::InvalidateOnUpdate);
 }
 
 void ClangdServer::applyTweak(PathRef File, Range Sel, StringRef TweakID,
                               Callback<Tweak::Effect> CB) {
-  // Tracks number of times a tweak has been applied.
+  // Tracks number of times a tweak has been attempted.
   static constexpr trace::Metric TweakAttempt(
       "tweak_attempt", trace::Metric::Counter, "tweak_id");
+  // Tracks number of times a tweak has failed to produce edits.
+  static constexpr trace::Metric TweakFailed(
+      "tweak_failed", trace::Metric::Counter, "tweak_id");
   TweakAttempt.record(1, TweakID);
   auto Action = [File = File.str(), Sel, TweakID = TweakID.str(),
                  CB = std::move(CB),
                  this](Expected<InputsAndAST> InpAST) mutable {
     if (!InpAST)
       return CB(InpAST.takeError());
     auto Selections = tweakSelection(Sel, *InpAST);
     if (!Selections)
if (*Effect) {
       // Tweaks don't apply clang-format, do that centrally here.
       for (auto &It : (*Effect)->ApplyEdits) {
         Edit &E = It.second;
         format::FormatStyle Style =
             getFormatStyleForFile(File, E.InitialCode, TFS);
         if (llvm::Error Err = reformatEdit(E, Style))
           elog("Failed to format {0}: {1}", It.first(), std::move(Err));
       }
+    } else {
+      TweakFailed.record(1, TweakID);
     }
     return CB(std::move(*Effect));
   };
   WorkScheduler.runWithAST("ApplyTweak", File, std::move(Action));
 }
 
 void ClangdServer::locateSymbolAt(PathRef File, Position Pos,
                                   Callback<std::vector<LocatedSymbol>> CB) {