[GHC] #15677: Valid hole fits and GADT type variable names

[GHC]

#15677: Valid hole fits and GADT type variable names
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        Reporter:  RyanGlScott       |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.8.1
       Component:  Compiler          |              Version:  8.6.1
      Resolution:                    |             Keywords:  TypedHoles,
                                     |  GADTs
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Poor/confusing    |  Unknown/Multiple
  error message                      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #9091             |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by Tritlo):

 Well, at least the situation for #9091 is a bit better now, with
 constraints shown by default:


 {{{
 tritlo at nietzsche:~/Code$ ghc t9091.hs -XGADTs
 [1 of 1] Compiling T9091            ( t9091.hs, t9091.o )

 t9091.hs:7:9: error:
     • Found hole: _ :: Int
     • In the expression: _
       In an equation for ‘h’: h Y x = _
     • Relevant bindings include
         x :: a (bound at t9091.hs:7:5)
         h :: X a -> a -> a (bound at t9091.hs:7:1)
       Constraints include a ~ Int (from t9091.hs:7:3)
       Valid hole fits include
         x :: a (bound at t9091.hs:7:5)
         maxBound :: forall a. Bounded a => a
           with maxBound @Int
           (imported from ‘Prelude’ at t9091.hs:1:8-12
            (and originally defined in ‘GHC.Enum’))
         minBound :: forall a. Bounded a => a
           with minBound @Int
           (imported from ‘Prelude’ at t9091.hs:1:8-12
            (and originally defined in ‘GHC.Enum’))
   |
 7 | h Y x = _

 }}}

 but this is still an issue.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15677#comment:2>
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