anchor.diff:    final bool _mergesAllDescendants;
   
     @override
  -  SemanticsNode establishSemanticsNode(_SemanticsGeometry geometry, SemanticsNode currentSemantics, SemanticsNode parentSemantics) {
  +  SemanticsNode establishSemanticsNode(_SemanticsGeometry geometry, SemanticsNode currentSemantics) {
       renderObjectOwner._semantics ??= new SemanticsNode(
         handler: renderObjectOwner is SemanticsActionHandler ? renderObjectOwner as dynamic : null,
         showOnScreen: renderObjectOwner.showOnScreen,
  
positive.code:       children.addAll(child.compile(
          geometry: createSemanticsGeometryForChild(geometry),
          currentSemantics: _children.length > 1 ? null : node,
          parentSemantics: node,
        ));
      }
      yield* finalizeSemanticsNode(node, children);
    }
  
    SemanticsNode establishSemanticsNode(_SemanticsGeometry geometry, SemanticsNode currentSemantics, SemanticsNode parentSemantics);
    Iterable<SemanticsNode> finalizeSemanticsNode(SemanticsNode node, List<SemanticsNode> children);
    _SemanticsGeometry createSemanticsGeometryForChild(_SemanticsGeometry geometry);
  }
  
negative.code:   final bool _mergesAllDescendants;
  
    @override
    SemanticsNode establishSemanticsNode(_SemanticsGeometry geometry, SemanticsNode currentSemantics) {
      SemanticsNode node;
      assert(_introducesOwnNode == null);
      assert(annotator != null || _mergesAllDescendants);
  