[GHC] #16381: Regression: Implicitly kind variables not in scope

[GHC]

#16381: Regression: Implicitly kind variables not in scope
-------------------------------------+-------------------------------------
           Reporter:  bgamari        |             Owner:  (none)
               Type:  bug            |            Status:  new
           Priority:  highest        |         Milestone:  8.10.1
          Component:  Compiler       |           Version:  8.9
  (Type checker)                     |
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 Our new `head.hackage` CI infrastructure has caught its first regression,
 it seems. A number of packages now fail to build due to out-of-scope kind
 variables. For instance, `singleton-bool`:
 {{{
 [1 of 1] Compiling Data.Singletons.Bool ( src/Data/Singletons/Bool.hs,
 dist/build/Data/Singletons/Bool.o )
 *** Parser [Data.Singletons.Bool]:
 Parser [Data.Singletons.Bool]: alloc=4264704 time=6.901
 *** Renamer/typechecker [Data.Singletons.Bool]:
 Renamer/typechecker [Data.Singletons.Bool]: alloc=17554720 time=92.794

 src/Data/Singletons/Bool.hs:119:29: error:
     Not in scope: type variable ‘k’
     |
 119 | sboolEqRefl :: forall (a :: k) (b :: k). SBoolI (a == b) => Maybe (a
 :~: b)
     |                             ^

 src/Data/Singletons/Bool.hs:119:38: error:
     Not in scope: type variable ‘k’
     |
 119 | sboolEqRefl :: forall (a :: k) (b :: k). SBoolI (a == b) => Maybe (a
 :~: b)
     |                                      ^
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/16381>
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