prefer_mixin support for nonfunction-type-aliases

lib/src/rules/prefer_mixin.dart

@@ -65,7 +65,10 @@ class _Visitor extends SimpleAstVisitor<void> {
   @override
   void visitWithClause(WithClause node) {
     for (var type in node.mixinTypes) {
-      final element = type.name.staticElement;
+      var element = type.name.staticElement;
+      if (element is TypeAliasElement) {
+        element = element.aliasedType.element;
+      }
       if (element is ClassElement && !element.isMixin && !isAllowed(element)) {
         rule.reportLint(type);
       }

pubspec.yaml

@@ -9,7 +9,7 @@ repository: https://github.com/dart-lang/linter
 documentation: https://dart-lang.github.io/linter/lints
 
 environment:
-  sdk: '>=2.12.0-0 <3.0.0'
+  sdk: '>=2.13.0-0 <3.0.0'
 
 dependencies:
   analyzer: ^1.1.0

test/rules/experiments/nonfunction-type-aliases/analysis_options.yaml

@@ -0,0 +1,3 @@
+analyzer:
+  enable-experiment:
+    - nonfunction-type-aliases

test/rules/experiments/nonfunction-type-aliases/rules/prefer_mixin.dart

@@ -0,0 +1,37 @@
+// Copyright (c) 2018, the Dart project authors. Please see the AUTHORS file
+// 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.
+
+// test w/ `pub run test -N prefer_mixin`
+
+import 'dart:collection';
+
+import 'dart:convert';
+
+class A {}
+
+class B extends Object with A {} // LINT
+
+mixin M {}
+
+class C with M {} // OK
+
+abstract class I with IterableMixin {} //OK
+
+abstract class L with ListMixin {} //OK
+
+abstract class MM with MapMixin {} //OK
+
+abstract class S with SetMixin {} //OK
+
+abstract class SCS with StringConversionSinkMixin {} //OK
+
+// nonfunction-type-aliases
+
+typedef AA = A;
+
+abstract class CC with AA { } // LINT
+
+typedef AAA = M;
+
+abstract class CCC with AAA { } //OK