[GHC] #16221: Core Lint error with a data type

23 Jan 2019

      #16221: Core Lint error with a data type
-------------------------------------+-------------------------------------
           Reporter:  monoidal       |             Owner:  (none)
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.7
  (Type checker)                     |
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  Compile-time
  Unknown/Multiple                   |  crash or panic
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
-------------------------------------+-------------------------------------
 The following data declaration fails `-dcore-lint`

 {{{
 #!haskell
 {-# LANGUAGE PolyKinds, ExplicitForAll, ExistentialQuantification #-}

 module T16221 where
 data T0 a = forall k (b :: k). MkT0 (T0 b) !Int
 }}}

 The test case was extracted from T14066a, the bang is to force the data
 type to have a wrapper. This has been present at least since GHC 8.0.

 {{{
 <no location info>: warning:
     In the type ‘T0 a_a1wY’
     Kind application error in type ‘T0 a_a1wY’
       Function kind = forall k. k -> *
       Arg kinds = [(k_X1x2, *), (a_a1wY, k_a1wZ)]
     Fun: k_X1x2
          (a_a1wY, k_a1wZ)
 <no location info>: warning:
     In the expression: MkT0
                          @ k_X1x2 @ a_a1wY @ k_X1x2 @ b_a1x0 dt_a1xC
 dt_X1xK
     Kinds don't match in type application:
     Type variable: a_X1xw :: k_X1x2
     Arg type: a_a1wY :: k_a1wZ
     Linted Arg kind: k_a1wZ
 <no location info>: warning:
     In the type ‘T0 a_a1wY’
     Kind application error in type ‘T0 a_a1wY’
       Function kind = forall k. k -> *
       Arg kinds = [(k_X1x2, *), (a_a1wY, k_a1wZ)]
     Fun: k_X1x2
          (a_a1wY, k_a1wZ)
 <no location info>: warning:
     In the expression: MkT0
                          @ k_X1x2 @ a_a1wY @ k_X1x2 @ b_a1x0 dt_a1xC
 dt_X1xK
     Kinds don't match in type application:
     Type variable: a_X1xw :: k_X1x2
     Arg type: a_a1wY :: k_a1wZ
     Linted Arg kind: k_a1wZ
 }}}

-- 
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/16221
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