anchor.diff:  ///
   /// Clients may not extend, implement or mix-in this class.
   class TypeAliasElementImpl extends _ExistingElementImpl
  -    with TypeParameterizedElementMixin
  +    with TypeParameterizedElementMixin, HasCompletionData
       implements TypeAliasElement {
     /// Is `true` if the element has direct or indirect reference to itself
     /// from anywhere except a class element or type parameter bounds.
  
positive.code: 
  /// A concrete implementation of a [FieldElement].
  class FieldElementImpl extends PropertyInducingElementImpl
      implements FieldElement {
    /// True if this field inherits from a covariant parameter. This happens
    /// when it overrides a field in a supertype that is covariant.
  
negative.code: 
  /// A concrete implementation of an [ExtensionElement].
  class ExtensionElementImpl extends _ExistingElementImpl
      with TypeParameterizedElementMixin, HasCompletionData
      implements ExtensionElement {
    /// The type being extended.
    DartType? _extendedType;
  