[GHC] #14498: GHC internal error: "not in scope during TC but it passed the renamer"

[GHC]

#14498: GHC internal error: "not in scope during TC but it passed the renamer"
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        Reporter:  Iceland_jack      |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler (Type    |              Version:  8.2.1
  checker)                           |             Keywords:
      Resolution:                    |  PatternSynonyms
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Compile-time      |  Unknown/Multiple
  crash or panic                     |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #14288            |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by RyanGlScott):

 Replying to [comment:3 simonpj]:
 > Short term: GHC should not crash.  Maybe it should just reject the
 program.

 I agree that until we implement #14288, this shouldn't crash. In fact,
 given that `kk` doesn't technically scope over the pattern at the moment,
 I'm surprised that GHC doesn't come up with a fresh `kk` type variable in
 the pattern `(App (Typeable :: TypeRep (a::kk -> k')) n)` (in fact, if you
 change it to `(App (Typeable :: TypeRep (a::kk2 -> k')) n)`, then it
 compiles). This makes me suspect that the code which renamed pattern
 synonyms is doing something suspicious at the moment.

 > Slightly longer term: we need to decide if we want to adopt the proposal
 in commment:15 of #14288.  Would this be worth a short GHC proposal?  It's
 certainly a change in the surface language.

 To answer your two questions:

 * Yes. I've been lacking the free time to look at comment:15 of #14288,
 but perhaps I can take a look this week.
 * I suppose we could put this forth as a proposal.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14498#comment:4>
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