anchor.diff:        }
       }
       try {
  -      _checkForAllInvalidOverrideErrorCodesForField(node);
         return super.visitFieldDeclaration(node);
       } finally {
         _isInStaticVariableDeclaration = false;
  
positive.code:     }
      return false;
    }
  
    bool _isUserDefinedObject(EvaluationResultImpl result) =>
        result == null ||
        (result.value != null && result.value.isUserDefinedObject);
  
    /**
     * Check that the given class [element] is not a superinterface to itself. The
  
negative.code: 
    void _checkMixinInference(
        NamedCompilationUnitMember node, WithClause withClause) {
      if (withClause == null || !_options.enableSuperMixins) {
        return;
      }
      ClassElement classElement = node.element;
      var type = classElement.type;
      var supertype = classElement.supertype;
  