[element model] migrate avoid_returning_null_for_void

Bug: https://github.com/dart-lang/linter/issues/5099
Change-Id: I703e246e05738a9a42aa8bdaeae2c675486e6c5e
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/391842
Auto-Submit: Phil Quitslund <[email protected]>
Commit-Queue: Phil Quitslund <[email protected]>
Commit-Queue: Brian Wilkerson <[email protected]>
Reviewed-by: Brian Wilkerson <[email protected]>

Author: pq

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

@@ -4,6 +4,7 @@
 
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/visitor.dart';
+import 'package:analyzer/dart/element/element2.dart';
 import 'package:analyzer/dart/element/type.dart';
 
 import '../analyzer.dart';
@@ -50,22 +51,20 @@ class _Visitor extends SimpleAstVisitor<void> {
   }
 
   void _visit(AstNode node, Expression expression) {
-    if (expression is! NullLiteral) {
-      return;
-    }
+    if (expression is! NullLiteral) return;
 
     var parent = node.thisOrAncestorMatching(
         (e) => e is FunctionExpression || e is MethodDeclaration);
     if (parent == null) return;
 
     var (type, isAsync, code) = switch (parent) {
       FunctionExpression() => (
-          parent.declaredElement?.returnType,
+          parent.element?.returnType,
           parent.body.isAsynchronous,
           LinterLintCode.avoid_returning_null_for_void_from_function,
         ),
       MethodDeclaration() => (
-          parent.declaredElement?.returnType,
+          parent.declaredFragment?.element.returnType,
           parent.body.isAsynchronous,
           LinterLintCode.avoid_returning_null_for_void_from_method,
         ),
@@ -82,3 +81,8 @@ class _Visitor extends SimpleAstVisitor<void> {
     }
   }
 }
+
+extension on FunctionExpression {
+  ExecutableElement2? get element =>
+      declaredFragment?.element ?? declaredElement2;
+}