anchor.diff:  }
   
   extension B_Ext on B {
  -  void /*2*/ a() { }
  +  void a() { }
   }
   
   f() {
  
positive.code: }
  
  extension Core2_Ext on Core2 {
    void /*2*/ a() => 0;
  }
  
  f() {
  
negative.code: import 'package:analyzer/dart/analysis/features.dart';
  import 'package:analyzer/src/error/codes.dart';
  import 'package:analyzer/src/generated/engine.dart';
  import 'package:test_reflective_loader/test_reflective_loader.dart';
  
  import 'driver_resolution.dart';
  