anchor.diff:  import 'package:analyzer/dart/element/element.dart';
   import 'package:analyzer/dart/element/type.dart';
   import 'package:analyzer/dart/element/type_provider.dart';
  -import 'package:analyzer/error/error.dart';
   import 'package:analyzer/error/listener.dart';
   import 'package:analyzer/src/dart/ast/ast.dart'
       show PrefixedIdentifierImpl, SimpleIdentifierImpl;
  
positive.code:     // Example: `y += voidFn()`, not allowed.
      if (operatorType != TokenType.EQ) {
        if (staticType != null && staticType.isVoid) {
          _recordUndefinedToken(
              null, StaticWarningCode.USE_OF_VOID_RESULT, operator, []);
          return;
        }
      }
  
negative.code:             node,
              [element.name]);
        } else if (node.name == "await" && _resolver.enclosingFunction != null) {
          _errorReporter.reportErrorForNode(
            StaticWarningCode.UNDEFINED_IDENTIFIER_AWAIT,
            node,
            [_resolver.enclosingFunction.displayName],
          );
        } else if (!_resolver.nameScope.shouldIgnoreUndefined(node)) {
          _errorReporter.reportErrorForNode(
            StaticWarningCode.UNDEFINED_IDENTIFIER,
            node,
            [node.name],
          );
        }
      }
      node.staticElement = element;
  