fix(ddtrace/internal): log to debug instead of warning when starting spans without an active tracer (#3513)

Author: darccio

ddtrace/internal/globaltracer.go

@@ -47,7 +47,7 @@ type NoopTracer struct{}
 
 // StartSpan implements ddtrace.Tracer.
 func (NoopTracer) StartSpan(_ string, _ ...ddtrace.StartSpanOption) ddtrace.Span {
-	log.Warn("Tracer must be started before starting a span; Review the docs for more information: https://docs.datadoghq.com/tracing/trace_collection/library_config/go/")
+	log.Debug("Tracer must be started before starting a span; Review the docs for more information: https://docs.datadoghq.com/tracing/trace_collection/library_config/go/")
 	return NoopSpan{}
 }
 

ddtrace/tracer/tracer_test.go

@@ -2708,6 +2708,9 @@ func TestNoopTracerStartSpan(t *testing.T) {
 	undo := log.UseLogger(customLogger{l: llog.New(w, "", llog.LstdFlags)})
 	defer undo()
 
+	log.SetLevel(log.LevelDebug)
+	defer log.SetLevel(log.LevelWarn)
+
 	StartSpan("abcd")
 
 	w.Close()