fix: allow exit spans to have child spans with the same type and subtype

span.go

@@ -65,7 +65,7 @@ func (tx *Transaction) StartSpan(name, spanType string, parent *Span) *Span {
 // span type, subtype, and action; a single dot separates span type and
 // subtype, and the action will not be set.
 func (tx *Transaction) StartSpanOptions(name, spanType string, opts SpanOptions) *Span {
-	if tx == nil || opts.parent.IsExitSpan() {
+	if tx == nil {
 		return newDroppedSpan()
 	}
 
@@ -345,6 +345,16 @@ func (s *Span) End() {
 	if s.Type == "" {
 		s.Type = "custom"
 	}
+	if s.parent.IsExitSpan() {
+		s.Context.model.Destination = nil
+		s.Context.model.Service = nil
+
+		if s.Type != s.parent.Type || s.Subtype != s.parent.Subtype {
+			s.dropWhen(true)
+			s.end()
+			return
+		}
+	}
 	if s.exit && !s.Context.setDestinationServiceCalled {
 		// The span was created as an exit span, but the user did not
 		// manually set the destination.service.resource

span_test.go

@@ -235,13 +235,22 @@ func TestStartExitSpan(t *testing.T) {
 	defer tracer.Close()
 
 	tx := tracer.StartTransaction("name", "type")
+
 	span := tx.StartSpanOptions("name", "type", apm.SpanOptions{ExitSpan: true})
 	assert.True(t, span.IsExitSpan())
+
 	// when the parent span is an exit span, any children should be noops.
-	span2 := tx.StartSpan("name", "type", span)
+	span2 := tx.StartSpan("name", "differenttype", span)
+	span2.End()
 	assert.True(t, span2.Dropped())
+
+	// Exit spans MAY have child spans that have the same `type` and `subtype`.
+	span3 := tx.StartSpan("name", "type", span)
+	span3.End()
+	assert.False(t, span3.Dropped())
+
 	span.End()
-	span2.End()
+
 	// Spans should still be marked as an exit span after they've been
 	// ended.
 	assert.True(t, span.IsExitSpan())