fix override checking of mixins

pkg/analyzer/test/src/task/strong/checker_test.dart

 // Copyright (c) 2015, 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 analyzer.test.src.task.strong.checker_test;
 
 import 'package:test_reflective_loader/test_reflective_loader.dart';
 
 import 'strong_test_helper.dart';
 
@@ skipping 2643 matching lines @@
 abstract class D extends Object with M<num> {}
 class E extends D with M<int> {
   /*error:INVALID_METHOD_OVERRIDE*/int x;
 }
 class F extends D with M<int> {
   num x;
 }
     ''');
   }
 
+  test_interfacesFromMixinsOnlyConsiderMostDerivedMember() {
+    // Regression test for dart2js interface pattern in strong mode.
+    return checkFile(r'''
+abstract class I1 { num get x; } 
+abstract class I2 extends I1 { int get x; }
+
+class M1 { num get x => 0; }
+class M2 { int get x => 0; }
+
+class Base extends Object with M1 implements I1 {}
+class Child extends Base with M2 implements I2 {}
+
+class C extends Object with M1, M2 implements I1, I2 {}
+    ''');
+  }
+
   test_invalidOverrides_baseClassOverrideToChildInterface() async {
     await checkFile('''
 class A {}
 class B {}
 
 abstract class I {
     m(A a);
 }
 
 class Base {
@@ skipping 606 matching lines @@
 }
 
 class Base {
     m(B a) {}
 }
 
 class M {
     m(B a) {}
 }
 
-// Here we want to report both, because the error location is
-// different.
-// TODO(sigmund): should we merge these as well?
+// TODO(jmesserly): the `INCONSISTENT_METHOD_INHERITANCE` message is from the
+// Dart 1 checking logic (using strong mode type system), it is not produced
+// by the strong mode OverrideChecker.
 class /*error:INCONSISTENT_METHOD_INHERITANCE*/T1
-    /*error:INVALID_METHOD_OVERRIDE_FROM_BASE*/extends Base
+    extends Base
     with /*error:INVALID_METHOD_OVERRIDE_FROM_MIXIN*/M
     implements I1 {}
 
-
-// Here we want to report both, because the error location is
-// different.
-// TODO(sigmund): should we merge these as well?
 class /*error:INCONSISTENT_METHOD_INHERITANCE*/U1 =
-    /*error:INVALID_METHOD_OVERRIDE_FROM_BASE*/Base
+    Base
     with /*error:INVALID_METHOD_OVERRIDE_FROM_MIXIN*/M
     implements I1;
 ''');
   }
 
   test_noDuplicateReports_twoGrandTypesOverrideSameMethodInInterface() async {
     await checkFile('''
 class A {}
 class B {}
 
@@ skipping 30 matching lines @@
 }
 
 class M1 {
     m(B a) {}
 }
 
 class M2 {
     m(B a) {}
 }
 
-// Here we want to report both, because the error location is
-// different.
-// TODO(sigmund): should we merge these as well?
 class /*error:INCONSISTENT_METHOD_INHERITANCE*/T1 extends Object
-    with /*error:INVALID_METHOD_OVERRIDE_FROM_MIXIN*/M1,
+    with M1,
     /*error:INVALID_METHOD_OVERRIDE_FROM_MIXIN*/M2
     implements I1 {}
 ''');
   }
 
   test_noDuplicateReports_typeAndBaseTypeOverrideSameMethodInInterface() async {
     await checkFile('''
 class A {}
 class B {}
 
@@ skipping 1018 matching lines @@
 class CheckerTest_Driver extends CheckerTest {
   @override
   bool get enableNewAnalysisDriver => true;
 
   @failingTest
   @override
   test_covariantOverride_fields() async {
     await super.test_covariantOverride_fields();
   }
 }