[clangd] workspace/symbol should be async, it reads from the index.

[sammccall]

Summary

To enable this, TUScheduler has to provide a way to run async tasks without
needing a preamble or AST!

[ilya-biryukov]

unittests/clangd/TUSchedulerTests.cpp

541

NIT: maybe simplify to ++Counter?

[ilya-biryukov]

LGTM

clangd/ClangdServer.cpp

 
 void ClangdServer::onFileEvent(const DidChangeWatchedFilesParams &Params) {
   // FIXME: Do nothing for now. This will be used for indexing and potentially
   // invalidating other caches.
 }
 
 void ClangdServer::workspaceSymbols(
     StringRef Query, int Limit, Callback<std::vector<SymbolInformation>> CB) {
-  CB(clangd::getWorkspaceSymbols(Query, Limit, Index,
+  std::string QueryCopy = Query;
+  WorkScheduler.run(
+      "getWorkspaceSymbols",
+      Bind(
+          [QueryCopy, Limit, this](decltype(CB) CB) {
+            CB(clangd::getWorkspaceSymbols(QueryCopy, Limit, Index,
                                            WorkspaceRoot.getValueOr("")));
+          },
+          std::move(CB)));
 }
 
 void ClangdServer::documentSymbols(
     StringRef File, Callback<std::vector<SymbolInformation>> CB) {
   auto Action = [](Callback<std::vector<SymbolInformation>> CB,
                    Expected<InputsAndAST> InpAST) {
     if (!InpAST)
       return CB(InpAST.takeError());

clangd/TUScheduler.h

public:
   /// FIXME(ibiryukov): remove the callback from this function.
   void update(PathRef File, ParseInputs Inputs, WantDiagnostics WD,
               llvm::unique_function<void(std::vector<Diag>)> OnUpdated);
 
   /// Remove \p File from the list of tracked files and schedule removal of its
   /// resources.
   void remove(PathRef File);
 
+  /// Schedule an async task with no dependencies.
+  void run(llvm::StringRef Name, llvm::unique_function<void()> Action);
+
   /// Schedule an async read of the AST. \p Action will be called when AST is
   /// ready. The AST passed to \p Action refers to the version of \p File
   /// tracked at the time of the call, even if new updates are received before
   /// \p Action is executed.
   /// If an error occurs during processing, it is forwarded to the \p Action
   /// callback.
   void runWithAST(llvm::StringRef Name, PathRef File,
                   Callback<InputsAndAST> Action);

clangd/TUScheduler.cpp

 
 void TUScheduler::remove(PathRef File) {
   bool Removed = Files.erase(File);
   if (!Removed)
     elog("Trying to remove file from TUScheduler that is not tracked: {0}",
          File);
 }
 
+void TUScheduler::run(StringRef Name, unique_function<void()> Action) {
+  if (!PreambleTasks)
+    return Action();
+  PreambleTasks->runAsync(Name, std::move(Action));
+}
+
 void TUScheduler::runWithAST(
     StringRef Name, PathRef File,
     unique_function<void(Expected<InputsAndAST>)> Action) {
   auto It = Files.find(File);
   if (It == Files.end()) {
     Action(make_error<LSPError>("trying to get AST for non-added document",
                                 ErrorCode::InvalidParams));
     return;

unittests/clangd/TUSchedulerTests.cpp

TEST_F(TUSchedulerTests, NoChangeDiags) {
   // Subsequent request does not get any diagnostics callback because the same
   // diags have previously been reported and the inputs didn't change.
   S.update(
       FooCpp, getInputs(FooCpp, Contents), WantDiagnostics::Auto,
       [&](std::vector<Diag>) { ADD_FAILURE() << "Should not be called."; });
   ASSERT_TRUE(S.blockUntilIdle(timeoutSeconds(10)));
 }
 
+TEST_F(TUSchedulerTests, Run) {
+  TUScheduler S(/*AsyncThreadsCount=*/getDefaultAsyncThreadsCount(),
+                /*StorePreambleInMemory=*/true, /*ASTCallbacks=*/nullptr,
+                /*UpdateDebounce=*/std::chrono::steady_clock::duration::zero(),
+                ASTRetentionPolicy());
+  std::atomic<int> Counter(0);
+  S.run("add 1", [&] { Counter.fetch_add(1); });
+  S.run("add 2", [&] { Counter.fetch_add(2); });
+  ASSERT_TRUE(S.blockUntilIdle(timeoutSeconds(10)));
+  EXPECT_EQ(Counter.load(), 3);
+}
+
 } // namespace
 } // namespace clangd
 } // namespace clang