Add tests for roles.

Many of the files modified are just wibbles to output, because now
tycons have roles attached to them, which are produced in the debugging
dumps.

1 files changed, 37 insertions, 0 deletions

diff --git a/testsuite/tests/deriving/should_fail/T7148a.hs b/testsuite/tests/deriving/should_fail/T7148a.hs
new file mode 100644
index 0000000000..6441058b24
--- /dev/null
+++ b/testsuite/tests/deriving/should_fail/T7148a.hs
@@ -0,0 +1,37 @@
+{-# LANGUAGE TypeFamilies, ScopedTypeVariables,
+             GeneralizedNewtypeDeriving #-}
+
+module T7148a where
+
+import Control.Monad.ST
+data Proxy a = Proxy
+type family Result a b
+ 
+class Convert a where
+  coerce :: Proxy b -> a -> Result a b
+ 
+newtype SAFE a = SAFE a
+type instance Result (SAFE a) b = a
+ 
+instance Convert (SAFE a) where
+  coerce _ (SAFE a) = a
+
+newtype IS_NO_LONGER a = IS_NO_LONGER a deriving Convert
+type instance Result (IS_NO_LONGER a) b = b
+
+--infered type is 
+unsafeCoerce :: forall a b. a -> b
+unsafeCoerce = coerce (Proxy :: Proxy b) . IS_NO_LONGER . SAFE
+
+--use it safely
+id' :: a -> a
+id' = unsafeCoerce
+ 
+--segfault (with high probability)
+crash :: segfault 
+crash = unsafeCoerce . tail . tail . tail . unsafeCoerce $ True
+
+
+--time for side effects
+unsafePerformIO :: IO a -> a
+unsafePerformIO x = runST $ unsafeCoerce x
\ No newline at end of file