[element model] migrate avoid_returning_this

Bug:  https://github.com/dart-lang/linter/issues/5099
Change-Id: Ia746475aaa29bae8be14a8c408adf728e77e015e
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/390081
Auto-Submit: Phil Quitslund <[email protected]>
Reviewed-by: Brian Wilkerson <[email protected]>
Commit-Queue: Brian Wilkerson <[email protected]>
Commit-Queue: Phil Quitslund <[email protected]>

Author: pq

pkg/linter/analyzer_use_new_elements.txt

@@ -31,6 +31,7 @@ lib/src/rules/avoid_relative_lib_imports.dart
 lib/src/rules/avoid_return_types_on_setters.dart
 lib/src/rules/avoid_returning_null.dart
 lib/src/rules/avoid_returning_null_for_future.dart
+lib/src/rules/avoid_returning_this.dart
 lib/src/rules/avoid_shadowing_type_parameters.dart
 lib/src/rules/avoid_single_cascade_in_expression_statements.dart
 lib/src/rules/avoid_slow_async_io.dart
@@ -346,6 +347,8 @@ test/rules/prefer_inlined_adds_test.dart
 test/rules/prefer_int_literals_test.dart
 test/rules/prefer_interpolation_to_compose_strings_test.dart
 test/rules/prefer_is_empty_test.dart
+test/rules/prefer_is_not_empty_test.dart
+test/rules/prefer_is_not_operator_test.dart
 test/rules/prefer_iterable_whereType_test.dart
 test/rules/prefer_mixin_test.dart
 test/rules/prefer_null_aware_method_calls_test.dart
@@ -442,9 +445,6 @@ test/verify_reflective_test_suites_test.dart
 test_data/rules/no_default_cases.dart
 test_data/rules/overridden_fields.dart
 test_data/rules/prefer_const_declarations.dart
-test_data/rules/prefer_final_fields.dart
-test_data/rules/prefer_is_not_empty.dart
-test_data/rules/prefer_is_not_operator.dart
 test_data/rules/prefer_void_to_null.dart
 test_data/rules/require_trailing_commas.dart
 test_data/rules/type_init_formals.dart

pkg/linter/lib/src/rules/avoid_returning_this.dart

@@ -2,9 +2,9 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/visitor.dart';
 import 'package:analyzer/dart/element/type.dart';
+import 'package:analyzer/src/dart/ast/ast.dart'; // ignore: implementation_imports
 
 import '../analyzer.dart';
 import '../extensions.dart';
@@ -79,10 +79,11 @@ class _Visitor extends SimpleAstVisitor<void> {
         return;
       }
 
-      var returnType = node.declaredElement?.returnType;
+      var returnType = node.declaredFragment?.element.returnType;
       if (returnType is InterfaceType &&
-          // ignore: cast_nullable_to_non_nullable
-          returnType.element == (parent as Declaration).declaredElement) {
+          returnType.element3 ==
+              // ignore: cast_nullable_to_non_nullable
+              (parent as FragmentDeclaration).declaredFragment?.element) {
       } else {
         return;
       }