Add test for GADTs and scoped type variables

tests/ghc-regress/gadt/all.T

@@ -64,6 +64,8 @@ test('data2', normal, compile, [''])
 test('termination', normal, compile, [''])
 test('set', normal, compile, [''])
 
+test('scoped', expect_broken(1823), compile, [''])
+
 
 # New ones from Dimitrios
 

tests/ghc-regress/gadt/scoped.hs

@@ -0,0 +1,33 @@
+{-# OPTIONS_GHC -XGADTs -XScopedTypeVariables -XPatternSignatures #-}
+
+-- Tests for scoped type variables and GADTs
+
+module GADT where
+
+data C x y where
+     C :: a -> C a a
+
+data D x y where
+     D :: C b c -> D a c
+
+-------  All these should be ok
+
+-- Rejected!
+g1 :: forall x y . C x y -> ()
+-- C (..) :: C x y
+-- Inside match on C, x=y
+g1 (C (p :: y)) = ()
+
+-- OK!
+g2 :: forall x y . C x y -> ()
+-- C (..) :: C x y
+-- Inside match on C, x=y
+g2 (C (p :: x)) = ()
+
+-- Rejected!
+g3 :: forall x y . D x y -> ()
+-- D (..)  :: D x y
+-- C (..)  :: C sk y
+--	sk = y
+-- p :: sk
+g3 (D (C (p :: y))) = ()