Elements. Deprecate ExtensionTypeElement.

Change-Id: Ia86a2b7b543fce9bec19583d7fe5d5d767c52d6a
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/418904
Reviewed-by: Paul Berry <[email protected]>
Commit-Queue: Konstantin Shcheglov <[email protected]>

Author: scheglov

pkg/analyzer/api.txt

@@ -3291,7 +3291,7 @@ package:analyzer/dart/element/element.dart:
     getGetter (method: PropertyAccessorElement? Function(String))
     getMethod (method: MethodElement? Function(String))
     getSetter (method: PropertyAccessorElement? Function(String))
-  ExtensionTypeElement (class extends Object implements InterfaceElement, experimental):
+  ExtensionTypeElement (class extends Object implements InterfaceElement, deprecated):
     new (constructor: ExtensionTypeElement Function())
     primaryConstructor (getter: ConstructorElement, deprecated)
     representation (getter: FieldElement)

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

@@ -1187,7 +1187,7 @@ abstract class ExtensionElement implements InstanceElement {
 /// An element that represents an extension type.
 ///
 /// Clients may not extend, implement or mix-in this class.
-@experimental
+@Deprecated('Use ExtensionTypeElement2 instead')
 abstract class ExtensionTypeElement implements InterfaceElement {
   /// The primary constructor of this extension.
   @Deprecated(elementModelDeprecationMsg)

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

@@ -4026,7 +4026,10 @@ class ExtensionElementImpl2 extends InstanceElementImpl2
 }
 
 class ExtensionTypeElementImpl extends InterfaceElementImpl
-    implements ExtensionTypeElement, ExtensionTypeFragment {
+    implements
+        // ignore:deprecated_member_use_from_same_package
+        ExtensionTypeElement,
+        ExtensionTypeFragment {
   late ExtensionTypeElementImpl2 augmentedInternal;
 
   @override

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

@@ -387,12 +387,6 @@ extension ExtensionElementImplExtension on ExtensionElementImpl {
   }
 }
 
-extension ExtensionTypeElement2Extension on ExtensionTypeElement2 {
-  ExtensionTypeElement get asElement {
-    return firstFragment as ExtensionTypeElement;
-  }
-}
-
 extension ExtensionTypeElementImpl2Extension on ExtensionTypeElementImpl2 {
   ExtensionTypeElementImpl get asElement {
     return firstFragment;