[element model] fix unsafe member to ExecutableFragment cast

Fixes: #57022

Bug: #57022
Change-Id: Icb00f89089565679109b749d1a43d95f4c8b09b6
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/393401
Commit-Queue: Phil Quitslund <[email protected]>
Reviewed-by: Konstantin Shcheglov <[email protected]>

Author: pq

pkg/analyzer/lib/src/dart/element/inheritance_manager3.dart

@@ -1286,8 +1286,8 @@ class Interface {
   /// The map of names to their signature in the interface.
   @experimental
   Map<Name, ExecutableElement2> get map2 {
-    return map.map((name, element) =>
-        MapEntry(name, (element as ExecutableFragment).element));
+    return map
+        .map((name, element) => MapEntry(name, element.asExecutableElement2));
   }
 
   /// Return `true` if the [name] is implemented in the supertype.

pkg/linter/test/rules/avoid_classes_with_only_static_members_test.dart

@@ -147,6 +147,16 @@ class C {
 ''');
   }
 
+  test_class_withGenericSuper() async {
+    // https://github.com/dart-lang/sdk/issues/57022
+    await assertNoDiagnostics(r'''
+class A<T> {
+  void m() {}
+}
+class C extends A<Object> { }
+''');
+  }
+
   test_class_withInstanceField() async {
     await assertNoDiagnostics(r'''
 class C {