Add test for Trac #1128

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

@@ -159,4 +159,5 @@ test('tcfail170', normal, compile_fail, [''])
 test('tcfail171', normal, compile_fail, [''])
 test('tcfail172', normal, compile_fail, [''])
 test('tcfail173', normal, compile_fail, [''])
+test('tcfail174', normal, compile_fail, [''])
 

testsuite/tests/ghc-regress/typecheck/should_fail/tcfail174.hs

+{-# OPTIONS -fglasgow-exts #-}
+
+module Foo where
+
+data Capture a = Base a
+               | Capture (Capture (forall x . x -> a))
+
+g :: Capture (forall a . a ->  a)
+g = Base id
+
+-- This function should definitely be rejected, with or without type signature
+
+h1 = Capture g
+
+h2 :: Capture b
+h2 = Capture g
+

testsuite/tests/ghc-regress/typecheck/should_fail/tcfail174.stderr

+
+tcfail174.hs:13:13:
+    Inferred type is less polymorphic than expected
+      Quantified type variable `a' escapes
+    When matching `forall a. a -> a'
+              and `forall a. a -> a1'
+      Expected type: Capture (forall x. x -> a)
+      Inferred type: Capture (forall a2. a2 -> a2)
+    In the first argument of `Capture', namely `g'
+
+tcfail174.hs:16:13:
+    Couldn't match expected type `b' (a rigid variable)
+	   against inferred type `a' (a rigid variable)
+      `b' is bound by the type signature for `h2' at tcfail174.hs:15:14
+    When matching `forall a. a -> a'
+              and `forall a. a -> b'
+      Expected type: Capture (forall x. x -> b)
+      Inferred type: Capture (forall a1. a1 -> a1)
+    In the first argument of `Capture', namely `g'