Test Trac #2721

testsuite/tests/ghc-regress/deriving/should_fail/T2721.hs

+{-# LANGUAGE TypeFamilies, GeneralizedNewtypeDeriving #-}
+
+-- Trac #2721
+
+module T2721 where
+
+class C a where
+  type T a
+  foo :: a -> T a
+
+instance C Int where
+  type T Int = Int
+  foo = id
+
+newtype N = N Int deriving(C)

testsuite/tests/ghc-regress/deriving/should_fail/T2721.stderr

+
+T2721.hs:15:27:
+    Can't make a derived instance of `C N'
+      (even with cunning newtype deriving:
+       the class has associated types)
+    In the newtype declaration for `N'

testsuite/tests/ghc-regress/deriving/should_fail/all.T

@@ -22,3 +22,4 @@ test('T2394', normal, compile_fail, [''])
 test('T2604', normal, compile_fail, [''])
 test('T2701', normal, compile_fail, [''])
 test('T2851', normal, compile_fail, [''])
+test('T2721', normal, compile_fail, [''])