reparent orphaned spans to grandparents

ctx.go

@@ -121,9 +121,17 @@ func newSpan(ctx context.Context, f *Func, args []interface{},
 		s.children.Iterate(func(child *Span) {
 			children = append(children, child)
 		})
+		s.children.Clear()
 		s.mtx.Unlock()
-		for _, child := range children {
-			child.orphan()
+
+		if s.parent != nil && !orphaned {
+			for _, child := range children {
+				s.parent.addChild(child)
+			}
+		} else {
+			for _, child := range children {
+				child.orphan()
+			}
 		}
 
 		if s.parent != nil {

span.go

@@ -34,18 +34,31 @@ type Annotation struct {
 
 func (s *Span) addChild(child *Span) {
 	s.mtx.Lock()
-	s.children.Add(child)
 	done := s.done
+	parent := s.parent
+	if !done {
+		s.children.Add(child)
+	}
 	s.mtx.Unlock()
+
 	if done {
-		child.orphan()
+		if parent == nil {
+			child.orphan()
+		} else {
+			parent.addChild(child)
+		}
 	}
 }
 
 func (s *Span) removeChild(child *Span) {
 	s.mtx.Lock()
+	parent := s.parent
 	s.children.Remove(child)
 	s.mtx.Unlock()
+
+	if parent != nil {
+		parent.removeChild(child)
+	}
 }
 
 func (s *Span) orphan() {

spanbag.go

@@ -23,6 +23,11 @@ type spanBag struct {
 	rest  map[*Span]int32
 }
 
+func (b *spanBag) Clear() {
+	b.first = nil
+	b.rest = nil
+}
+
 func (b *spanBag) Add(s *Span) {
 	if b.first == nil {
 		b.first = s