TypeInType fails to compile old code

{-#  LANGUAGE TypeInType              #-}

module PP where

newtype Field l v   =   Field { value :: v }

label  ::  Field l v -> l
label  =   undefined

class HEq x
hEq :: HEq x => x -> Int
hEq = undefined

class HListGet r where
    hListGet :: r -> Int
instance
    HEq l => HListGet (Field l v) where
    hListGet f = hEq (label f)

fails with

mini.hs:18:29: error:
    • Couldn't match type ‘k’ with ‘*’
      ‘k’ is a rigid type variable bound by
        the instance declaration at mini.hs:17:5-33
      Expected type: Field * l v
        Actual type: Field k l v
    • In the first argument of ‘label’, namely ‘f’
      In the first argument of ‘hEq’, namely ‘(label f)’
      In the expression: hEq (label f)
    • Relevant bindings include
        f :: Field k l v (bound at mini.hs:18:14)
        hListGet :: Field k l v -> Int (bound at mini.hs:18:5)
   |
18 |     hListGet f = hEq (label f)
   |

Trac metadata

Trac field	Value
Version	8.2.1-rc2
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system
Architecture