Add tests for type signature validity (cf Trac 2019)

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

@@ -182,4 +182,7 @@ test('tcfail190', if_compiler_lt('ghc', '6.9', skip), compile_fail, [''])
 test('tcfail191', if_compiler_lt('ghc', '6.9', skip), compile_fail, [''])
 test('tcfail192', if_compiler_lt('ghc', '6.9', skip), compile_fail, [''])
 test('tcfail193', if_compiler_lt('ghc', '6.9', skip), compile_fail, [''])
-test('tcfail194', if_compiler_lt('ghc', '6.9', skip), compile_fail, [''])
\ No newline at end of file
+test('tcfail194', if_compiler_lt('ghc', '6.9', skip), compile_fail, [''])
+test('tcfail195', normal, compile_fail, [''])
+test('tcfail196', normal, compile_fail, [''])
+test('tcfail197', normal, compile_fail, [''])

testsuite/tests/ghc-regress/typecheck/should_fail/tcfail127.stderr

 
 tcfail127.hs:3:0:
-    All of the type variables in the constraint `Num a'
-    are already in scope (at least one must be universally quantified here)
-	(Use -XFlexibleContexts to lift this restriction)
+    Illegal polymorphic or qualified type: (Num a) => a -> a
     In the type signature for `foo':
       foo :: IO ((Num a) => a -> a)

testsuite/tests/ghc-regress/typecheck/should_fail/tcfail195.hs

+{-# LANGUAGE RankNTypes, GADTs #-}
+
+module ShouldFail where
+
+data Foo a where
+  Foo :: Int -> Foo (forall a. a)

testsuite/tests/ghc-regress/typecheck/should_fail/tcfail195.stderr

+
+tcfail195.hs:6:2:
+    Illegal polymorphic or qualified type: forall a. a
+    In the definition of data constructor `Foo'
+    In the data type declaration for `Foo'

testsuite/tests/ghc-regress/typecheck/should_fail/tcfail196.hs

+{-# LANGUAGE RankNTypes #-}
+
+module ShouldFail where
+
+bar :: Num (forall a. a) => Int -> Int
+bar = error "urk"
+

testsuite/tests/ghc-regress/typecheck/should_fail/tcfail196.stderr

+
+tcfail196.hs:5:0:
+    Illegal polymorphic or qualified type: forall a. a
+    In the type signature for `bar':
+      bar :: (Num (forall a. a)) => Int -> Int

testsuite/tests/ghc-regress/typecheck/should_fail/tcfail197.hs

+{-# LANGUAGE RankNTypes #-}
+
+module ShouldFail where
+
+foo :: [forall a. a] -> Int
+foo = error "urk"
+

testsuite/tests/ghc-regress/typecheck/should_fail/tcfail197.stderr

+
+tcfail197.hs:5:0:
+    Illegal polymorphic or qualified type: forall a. a
+    In the type signature for `foo':
+      foo :: [forall a. a] -> Int