Invalid constraints should fail to type check

With ghc-7.6.3 the following code:

f :: Int => Int
f x = x + 1

should fail to type check, but instead compiles and runs as if it was:

f :: Int -> Int
f x = x + 1

With 7.8rc1 and git HEAD this results in an error:

Expected a constraint, but ‛Int’ has kind ‛*’
In the type signature for ‛f’: f :: Int => Int

We should add a "shouldn't type check" test to avoid the possibilty of a regression.

Also:

g :: (Int => Show a) => Int
g = undefined

Trac metadata

Trac field	Value
Version	7.6.3
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler (Type checker)
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