[clangd] Add a helper for exposing tracer status

clang-tools-extra/clangd/support/Trace.cpp

@@ -281,6 +281,8 @@ void log(const llvm::Twine &Message) {
   T->instant("Log", llvm::json::Object{{"Message", Message.str()}});
 }
 
+bool enabled() { return T != nullptr; }
+
 // The JSON object is event args (owned by context), if the tracer wants them.
 static std::pair<Context, llvm::json::Object *>
 makeSpanContext(llvm::Twine Name, const Metric &LatencyMetric) {

clang-tools-extra/clangd/support/Trace.h

@@ -128,6 +128,9 @@ std::unique_ptr<EventTracer> createCSVMetricTracer(llvm::raw_ostream &OS);
 /// Records a single instant event, associated with the current thread.
 void log(const llvm::Twine &Name);
 
+/// Returns true if there is an active tracer.
+bool enabled();
+
 /// Records an event whose duration is the lifetime of the Span object.
 /// This lifetime is extended when the span's context is reused.
 ///