[clangd] Fix a data race in TUScheduler

By recomputing CompilerInvocation instead of copying it.
The problem was caused by the fact that copies of CompilerInvocation
store references to the shared state (DiagnosticOptions) when copied,
causing data races when two different copies are destroyed from
different threads.

llvm-svn: 335836

clang-tools-extra/clangd/TUScheduler.cpp

@@ -221,8 +221,6 @@ private:
   Semaphore &Barrier;
   /// Inputs, corresponding to the current state of AST.
   ParseInputs FileInputs;
-  /// CompilerInvocation used for FileInputs.
-  std::unique_ptr<CompilerInvocation> Invocation;
   /// Size of the last AST
   /// Guards members used by both TUScheduler and the worker thread.
   mutable std::mutex Mutex;
@@ -325,7 +323,8 @@ void ASTWorker::update(ParseInputs Inputs, WantDiagnostics WantDiags,
         Inputs.CompileCommand.Directory + "] " +
         llvm::join(Inputs.CompileCommand.CommandLine, " "));
     // Rebuild the preamble and the AST.
-    Invocation = buildCompilerInvocation(Inputs);
+    std::unique_ptr<CompilerInvocation> Invocation =
+        buildCompilerInvocation(Inputs);
     if (!Invocation) {
       log("Could not build CompilerInvocation for file " + FileName);
       return;
@@ -341,8 +340,7 @@ void ASTWorker::update(ParseInputs Inputs, WantDiagnostics WantDiags,
     }
     // Build the AST for diagnostics.
     llvm::Optional<ParsedAST> AST =
-        buildAST(FileName, llvm::make_unique<CompilerInvocation>(*Invocation),
-                 Inputs, NewPreamble, PCHs);
+        buildAST(FileName, std::move(Invocation), Inputs, NewPreamble, PCHs);
     // We want to report the diagnostics even if this update was cancelled.
     // It seems more useful than making the clients wait indefinitely if they
     // spam us with updates.
@@ -362,6 +360,8 @@ void ASTWorker::runWithAST(
   auto Task = [=](decltype(Action) Action) {
     llvm::Optional<std::unique_ptr<ParsedAST>> AST = IdleASTs.take(this);
     if (!AST) {
+      std::unique_ptr<CompilerInvocation> Invocation =
+          buildCompilerInvocation(FileInputs);
       // Try rebuilding the AST.
       llvm::Optional<ParsedAST> NewAST =
           Invocation