[clang] Count references to DiagnosticOptions atomically

Author: jansvoboda11

clang-tools-extra/clangd/Preamble.cpp

@@ -673,7 +673,6 @@ buildPreamble(PathRef FileName, CompilerInvocation CI,
   // Reset references to ref-counted-ptrs before executing the callbacks, to
   // prevent resetting them concurrently.
   PreambleDiagsEngine.reset();
-  CI.DiagnosticOpts.reset();
 
   // When building the AST for the main file, we do want the function
   // bodies.

clang/include/clang/Basic/DiagnosticOptions.h

@@ -67,7 +67,8 @@ inline DiagnosticLevelMask operator&(DiagnosticLevelMask LHS,
 raw_ostream& operator<<(raw_ostream& Out, DiagnosticLevelMask M);
 
 /// Options for controlling the compiler diagnostics engine.
-class DiagnosticOptions : public RefCountedBase<DiagnosticOptions>{
+class DiagnosticOptions
+    : public llvm::ThreadSafeRefCountedBase<DiagnosticOptions> {
   friend bool ParseDiagnosticArgs(DiagnosticOptions &, llvm::opt::ArgList &,
                                   clang::DiagnosticsEngine *, bool);