Avoid traversing classes when looking for circular references in typedefs.

pkg/analyzer/test/generated/compile_time_error_code_test.dart

 // Copyright (c) 2014, 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.
 
 library engine.compile_time_error_code_test;
 
 import 'package:analyzer/src/generated/source_io.dart';
 import 'package:analyzer/src/generated/error.dart';
 import 'package:analyzer/src/generated/parser.dart' show ParserErrorCode;
 import 'package:analyzer/src/generated/engine.dart';
@@ skipping 4397 matching lines @@
   F foo(G g) => g;
 }''');
     resolve(source);
     assertErrors(source, [
         CompileTimeErrorCode.TYPE_ALIAS_CANNOT_REFERENCE_ITSELF,
         CompileTimeErrorCode.TYPE_ALIAS_CANNOT_REFERENCE_ITSELF,
         StaticTypeWarningCode.RETURN_OF_INVALID_TYPE]);
     verify([source]);
   }
 
+  void test_typeAliasCannotReferenceItself_19459() {
+    // A complex example involving multiple classes.  This is legal, since
+    // typedef F references itself only via a class.
+    Source source = addSource(r'''
+class A<B, C> {}
+abstract class D {
+  f(E e);
+}
+abstract class E extends A<dynamic, F> {}
+typedef D F();
+''');
+    resolve(source);
+    assertNoErrors(source);
+    verify([source]);
+  }
+
   void test_typeAliasCannotReferenceItself_parameterType_named() {
     Source source = addSource("typedef A({A a});");
     resolve(source);
     assertErrors(source, [CompileTimeErrorCode.TYPE_ALIAS_CANNOT_REFERENCE_ITSELF]);
     verify([source]);
   }
 
   void test_typeAliasCannotReferenceItself_parameterType_positional() {
     Source source = addSource("typedef A([A a]);");
     resolve(source);
     assertErrors(source, [CompileTimeErrorCode.TYPE_ALIAS_CANNOT_REFERENCE_ITSELF]);
     verify([source]);
   }
 
   void test_typeAliasCannotReferenceItself_parameterType_required() {
     Source source = addSource("typedef A(A a);");
     resolve(source);
     assertErrors(source, [CompileTimeErrorCode.TYPE_ALIAS_CANNOT_REFERENCE_ITSELF]);
     verify([source]);
   }
 
   void test_typeAliasCannotReferenceItself_parameterType_typeArgument() {
     Source source = addSource("typedef A(List<A> a);");
     resolve(source);
     assertErrors(source, [CompileTimeErrorCode.TYPE_ALIAS_CANNOT_REFERENCE_ITSELF]);
     verify([source]);
   }
 
   void test_typeAliasCannotReferenceItself_returnClass_withTypeAlias() {
+    // A typedef is allowed to indirectly reference itself via a class.
     Source source = addSource(r'''
 typedef C A();
 typedef A B();
 class C {
   B a;
 }''');
     resolve(source);
-    assertErrors(source, [CompileTimeErrorCode.TYPE_ALIAS_CANNOT_REFERENCE_ITSELF]);
+    assertNoErrors(source);
     verify([source]);
   }
 
   void test_typeAliasCannotReferenceItself_returnType() {
     Source source = addSource("typedef A A();");
     resolve(source);
     assertErrors(source, [CompileTimeErrorCode.TYPE_ALIAS_CANNOT_REFERENCE_ITSELF]);
     verify([source]);
   }
 
@@ skipping 295 matching lines @@
   void _check_wrongNumberOfParametersForOperator1(String name) {
     _check_wrongNumberOfParametersForOperator(name, "");
     _check_wrongNumberOfParametersForOperator(name, "a, b");
   }
 }
 
 main() {
   _ut.groupSep = ' | ';
   runReflectiveTests(CompileTimeErrorCodeTest);
 }