1 files changed, 33 insertions, 0 deletions
diff --git a/testsuite/tests/deriving/should_run/T3087.hs b/testsuite/tests/deriving/should_run/T3087.hs
new file mode 100644
index 0000000000..7cba3d9609
--- /dev/null
+++ b/testsuite/tests/deriving/should_run/T3087.hs
@@ -0,0 +1,33 @@
+{-# LANGUAGE RankNTypes, DeriveDataTypeable #-}
+
+module Main where
+
+import Data.Generics
+
+data MyMaybe a = MyNothing | MyJust a deriving (Data, Typeable)
+
+test1 :: ()
+test1 = undefined `ext1Q` (\ (Just _) -> ()) $ Just ()
+
+test1' :: ()
+test1' = undefined `ext1Q` (\ (MyJust _) -> ()) $ MyJust ()
+
+newtype Q r a = Q { unQ :: a -> r }
+
+ext2Q :: (Data d, Typeable2 t)
+      => (d -> q) -> (forall d1 d2. (Data d1, Data d2) => t d1 d2 -> q)
+      -> d -> q
+ext2Q def ext arg =
+  case dataCast2 (Q ext) of
+    Just (Q ext') -> ext' arg
+    Nothing       -> def arg
+
+data MyPair a b = MyPair a b deriving (Data, Typeable)
+
+test2 :: ()
+test2 = undefined `ext2Q` (\(_,_) -> ()) $ ((),())
+
+test2' :: ()
+test2' = undefined `ext2Q` (\(MyPair _ _) -> ()) $ MyPair () ()
+
+main = do { print test1; print test1'; print test2; print test2' }