[GHC] #11821: Internal error: not in scope during type checking, but it passed the renamer

[GHC]

#11821: Internal error: not in scope during type checking, but it passed the
renamer
-------------------------------------+-------------------------------------
        Reporter:  darchon           |                Owner:  (none)
            Type:  bug               |               Status:  closed
        Priority:  normal            |            Milestone:  8.0.2
       Component:  Compiler          |              Version:  8.0.1-rc3
      Resolution:  fixed             |             Keywords:  TypeInType
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  GHC rejects       |            Test Case:
  valid program                      |  polykinds/T11821, polykinds/T11821a
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D2146
       Wiki Page:                    |
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Comment (by mietek):

 I can still trigger the same internal error in GHC 8.0.2 with the
 following, admittedly silly example:
 {{{
 {-# LANGUAGE TypeInType #-}
 data X :: Y where Y :: X
 }}}
 The error message is:
 {{{
 Bug.hs:2:11: error: …
     • GHC internal error: ‘Y’ is not in scope during type checking, but it
 passed the renamer
       tcl_env of environment: [r1cR :-> APromotionErr TyConPE]
     • In the kind ‘Y’
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11821#comment:15>
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