Elements. Make FragmentImpl.element type ElementImpl.

Change-Id: I3a028685c850acb36108106ae034fa2d909d58bc
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/445740
Reviewed-by: Paul Berry <[email protected]>
Commit-Queue: Konstantin Shcheglov <[email protected]>

Author: scheglov

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

@@ -3402,6 +3402,9 @@ abstract class FragmentImpl with _FragmentImplMixin implements Fragment {
   /// is `f=`, instead of `f`.
   String get displayName => name ?? '';
 
+  @override
+  ElementImpl get element;
+
   /// Return the enclosing unit element (which might be the same as `this`), or
   /// `null` if this element is not contained in any compilation unit.
   LibraryFragmentImpl get enclosingUnit {
@@ -5463,7 +5466,8 @@ class LabelElementImpl extends ElementImpl implements LabelElement {
 }
 
 class LabelFragmentImpl extends FragmentImpl implements LabelFragment {
-  late final LabelElementImpl element2 = LabelElementImpl(this);
+  @override
+  late final LabelElementImpl element = LabelElementImpl(this);
 
   @override
   final String? name;
@@ -5492,9 +5496,6 @@ class LabelFragmentImpl extends FragmentImpl implements LabelFragment {
   @override
   String get displayName => name ?? '';
 
-  @override
-  LabelElement get element => element2;
-
   @override
   ExecutableFragmentImpl get enclosingFragment =>
       super.enclosingFragment as ExecutableFragmentImpl;

pkg/analyzer/lib/src/error/duplicate_definition_verifier.dart

@@ -324,7 +324,7 @@ class DuplicateDefinitionVerifier {
             ),
           );
         } else {
-          setterScope[lookupName] = fragment.element as ElementImpl;
+          setterScope[lookupName] = fragment.element;
         }
       }
     } else {
@@ -340,7 +340,7 @@ class DuplicateDefinitionVerifier {
           ),
         );
       } else {
-        getterScope[lookupName] = fragment.element as ElementImpl;
+        getterScope[lookupName] = fragment.element;
       }
     }
   }
@@ -599,7 +599,7 @@ class MemberDuplicateDefinitionVerifier {
     var scopeEntry = scope[name];
     switch (scopeEntry) {
       case null:
-        scope[name] = _ScopeEntryElement(fragment.element as ElementImpl);
+        scope[name] = _ScopeEntryElement(fragment.element);
       case _ScopeEntryElement(element: GetterElementImpl previous)
           when fragment is SetterFragmentImpl:
         scope[name] = _ScopeEntryGetterSetterPair(

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

@@ -160,7 +160,7 @@ extension ElementOrNullExtension on FragmentImpl? {
     } else if (self is InterfaceFragmentImpl) {
       return self.element;
     } else if (self is LabelFragmentImpl) {
-      return self.element2;
+      return self.element;
     } else if (self is LocalVariableFragmentImpl) {
       return self.element;
     } else if (self is NeverFragmentImpl) {