Elements. Deprecate MultiplyDefinedElement.

Change-Id: I0381d303f19f40c28ca61b57e8e9cf7b76be8d7b
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/418917
Commit-Queue: Konstantin Shcheglov <[email protected]>
Reviewed-by: Paul Berry <[email protected]>

Author: scheglov

pkg/analyzer/api.txt

@@ -3428,7 +3428,7 @@ package:analyzer/dart/element/element.dart:
     isBase (getter: bool)
     superclassConstraints (getter: List<InterfaceType>)
     isImplementableIn (method: bool Function(LibraryElement))
-  MultiplyDefinedElement (class extends Object implements Element):
+  MultiplyDefinedElement (class extends Object implements Element, deprecated):
     new (constructor: MultiplyDefinedElement Function())
     conflictingElements (getter: List<Element>)
   NamespaceCombinator (class extends Object):

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

@@ -564,7 +564,7 @@ abstract class Element implements AnalysisTarget {
   /// Library that contains this element.
   ///
   /// This will be the element itself if it is a library element. This will be
-  /// `null` if this element is [MultiplyDefinedElement] that is not contained
+  /// `null` if this element is [MultiplyDefinedElement2] that is not contained
   /// in a library.
   LibraryElement? get library;
 
@@ -1879,6 +1879,7 @@ abstract class MixinElement implements InterfaceElement {
 /// and will return useless results.
 ///
 /// Clients may not extend, implement or mix-in this class.
+@Deprecated('Use MultiplyDefinedElement2 instead')
 abstract class MultiplyDefinedElement implements Element {
   /// The elements that were defined within the scope to have the same name.
   List<Element> get conflictingElements;

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

@@ -8737,8 +8737,10 @@ enum Modifier {
   SYNTHETIC
 }
 
-/// A concrete implementation of a [MultiplyDefinedElement].
-class MultiplyDefinedElementImpl implements MultiplyDefinedElement {
+class MultiplyDefinedElementImpl
+    implements
+        // ignore:deprecated_member_use_from_same_package
+        MultiplyDefinedElement {
   /// The unique integer identifier of this element.
   @override
   final int id = ElementImpl._NEXT_ID++;