[ISSUE-5161] Fix panics if a nil context is provided to the .Start() method

Author: htemelski

internal/global/trace.go

@@ -136,6 +136,11 @@ func (t *tracer) setDelegate(provider trace.TracerProvider) {
 // Start implements trace.Tracer by forwarding the call to t.delegate if
 // set, otherwise it forwards the call to a NoopTracer.
 func (t *tracer) Start(ctx context.Context, name string, opts ...trace.SpanStartOption) (context.Context, trace.Span) {
+	if ctx == nil {
+		// Prevent trace.ContextWithSpan from panicking.
+		ctx = context.Background()
+	}
+
 	delegate := t.delegate.Load()
 	if delegate != nil {
 		return delegate.(trace.Tracer).Start(ctx, name, opts...)

trace/noop.go

@@ -43,6 +43,12 @@ func (t noopTracer) Start(ctx context.Context, name string, _ ...SpanStartOption
 		// span is likely already a noopSpan, but let's be sure
 		span = noopSpanInstance
 	}
+
+	if ctx == nil {
+		// Prevent trace.ContextWithSpan from panicking.
+		ctx = context.Background()
+	}
+
 	return ContextWithSpan(ctx, span), span
 }
 

trace/noop/noop.go

@@ -54,6 +54,11 @@ type Tracer struct{ embedded.Tracer }
 func (t Tracer) Start(ctx context.Context, _ string, _ ...trace.SpanStartOption) (context.Context, trace.Span) {
 	span := trace.SpanFromContext(ctx)
 
+	if ctx == nil {
+		// Prevent trace.ContextWithSpan from panicking.
+		ctx = context.Background()
+	}
+
 	// If the parent context contains a non-zero span context, that span
 	// context needs to be returned as a non-recording span
 	// (https://github.com/open-telemetry/opentelemetry-specification/blob/3a1dde966a4ce87cce5adf464359fe369741bbea/specification/trace/api.md#behavior-of-the-api-in-the-absence-of-an-installed-sdk).