Add test for Trac #4188

testsuite/tests/ghc-regress/th/T4188.hs

+{-# LANGUAGE TemplateHaskell, GADTs #-}
+
+module T4188 where
+
+import Language.Haskell.TH
+import IO
+
+class C a where {}
+
+data T1 a where
+  MkT1 :: a -> b -> T1 a
+
+data T2 a where
+  MkT2 :: (C a, C b) => a -> b -> T2 a
+
+data T3 x where
+  MkT3 :: (C x, C y) => x -> y -> T3 (x,y)
+
+$(do { dec1 <- reify ''T1
+     ; runIO (putStrLn (pprint dec1))
+     ; dec2 <- reify ''T2
+     ; runIO (putStrLn (pprint dec2))
+     ; dec3 <- reify ''T3
+     ; runIO (putStrLn (pprint dec3))
+     ; runIO (hFlush stdout)
+     ; return [] })
+
+   

testsuite/tests/ghc-regress/th/T4188.stderr

+data T4188.T1 a_0 = forall b_1 . T4188.MkT1 a_0 b_1
+data T4188.T2 a_0
+    = forall b_1 . (T4188.C a_0, T4188.C b_1) => T4188.MkT2 a_0 b_1
+data T4188.T3 x_0
+    = forall x_1 y_2 . (x_0 ~ (x_1, y_2), T4188.C x_1, T4188.C y_2) =>
+                       T4188.MkT3 x_1 y_2

testsuite/tests/ghc-regress/th/all.T

@@ -163,3 +163,4 @@ test('T3845', normal, compile, ['-v0'])
 test('T3899', extra_clean(['T3899a.hi','T3899a.o']), 
               multimod_compile, ['T3899','-v0 -ddump-splices -dsuppress-uniques'])
 test('T4056', normal, compile, ['-v0'])
+test('T4188', normal, compile, ['-v0'])