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