anchor.diff:    /// be `null` if there are no declarations in the compilation unit.
     CompilationUnitImpl(
         this.beginToken,
  -      ScriptTagImpl? scriptTag,
  +      this._scriptTag,
         List<Directive>? directives,
         List<CompilationUnitMember>? declarations,
         this.endToken,
         this.featureSet) {
  -    _scriptTag = _becomeParentOf(scriptTag);
  +    _becomeParentOf(_scriptTag);
       _directives._initialize(this, directives);
       _declarations._initialize(this, declarations);
     }
  
positive.code:   Token awaitKeyword;
  
    /// The expression whose value is being waited on.
    late ExpressionImpl _expression;
  
    /// Initialize a newly created await expression.
    AwaitExpressionImpl(this.awaitKeyword, ExpressionImpl expression) {
      _expression = _becomeParentOf(expression);
    }
  
    @override
  
negative.code:   Token? propertyKeyword;
  
    /// The function expression being wrapped.
    FunctionExpressionImpl _functionExpression;
  
    /// Initialize a newly created function declaration. Either or both of the
    /// [comment] and [metadata] can be `null` if the function does not have the
  