Elements. Deprecate TypeAliasElement.

Change-Id: I0cbcb9e3cf0fac76ebed59cabc4dc4b5205c78ae
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/418908
Commit-Queue: Konstantin Shcheglov <[email protected]>
Reviewed-by: Paul Berry <[email protected]>

Author: scheglov

pkg/analyzer/api.txt

@@ -3499,7 +3499,7 @@ package:analyzer/dart/element/element.dart:
     new (constructor: TopLevelVariableElement Function())
     declaration (getter: TopLevelVariableElement)
     isExternal (getter: bool)
-  TypeAliasElement (class extends Object implements TypeParameterizedElement, TypeDefiningElement):
+  TypeAliasElement (class extends Object implements TypeParameterizedElement, TypeDefiningElement, deprecated):
     new (constructor: TypeAliasElement Function())
     aliasedElement (getter: Element?, deprecated)
     aliasedType (getter: DartType)

pkg/analyzer/lib/dart/element/element.dart

@@ -2186,6 +2186,7 @@ abstract class TopLevelVariableElement implements PropertyInducingElement {
 /// A type alias (`typedef`).
 ///
 /// Clients may not extend, implement or mix-in this class.
+@Deprecated('Use TypeAliasElement2 instead')
 abstract class TypeAliasElement
     implements TypeParameterizedElement, TypeDefiningElement {
   /// If the aliased type has structure, return the corresponding element.

pkg/analyzer/lib/src/dart/element/element.dart

@@ -10985,8 +10985,13 @@ class TopLevelVariableElementImpl2 extends PropertyInducingElementImpl2
 ///
 /// Clients may not extend, implement or mix-in this class.
 class TypeAliasElementImpl extends _ExistingElementImpl
-    with AugmentableFragment, TypeParameterizedElementMixin
-    implements TypeAliasElement, TypeAliasFragment {
+    with
+        AugmentableFragment,
+        TypeParameterizedElementMixin
+    implements
+        // ignore:deprecated_member_use_from_same_package
+        TypeAliasElement,
+        TypeAliasFragment {
   @override
   String? name2;
 

pkg/analyzer/lib/src/utilities/extensions/element.dart

@@ -689,18 +689,6 @@ extension TopLevelVariableElementImpl2Extension
   }
 }
 
-extension TypeAliasElement2Extension on TypeAliasElement2 {
-  TypeAliasElement get asElement {
-    return firstFragment as TypeAliasElement;
-  }
-}
-
-extension TypeAliasElementExtension on TypeAliasElement {
-  TypeAliasElement2 get asElement2 {
-    return (this as TypeAliasElementImpl).element;
-  }
-}
-
 extension TypeAliasElementImpl2Extension on TypeAliasElementImpl2 {
   TypeAliasElementImpl get asElement {
     return firstFragment;