[GHC] #14845: TypeInType, index GADT by constraint witness

[GHC]

#14845: TypeInType, index GADT by constraint witness
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        Reporter:  Iceland_jack      |                Owner:  (none)
            Type:  feature request   |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.5
      Resolution:                    |             Keywords:  TypeInType
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #13895            |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by goldfire):

 Actually, come to think of it, the check I suggested around
 `dataConFullSig` will snag user-written equality constraints, which it
 shouldn't. For example

 {{{
 data G a where
   MkG :: a ~ Int => G a
 }}}

 should be just fine to promote. So something more delicate will be needed.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14845#comment:16>
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