[GHC] #14422: {-# complete #-} should be able to be at least partially type directed

[GHC]

#14422: {-# complete #-} should be able to be at least partially type directed
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           Reporter:  ekmett         |             Owner:  (none)
               Type:  feature        |            Status:  new
  request                            |
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.2.1
  (Type checker)                     |
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:  8779
Differential Rev(s):                 |         Wiki Page:
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 The fact that `{-# complete #-}` pragma that was added in#8779 is tied to
 the set of patterns only and not the types involved can make it rather
 awkward or impossible to use in practice.

 Say I have a bunch of types that happen to share a common `(:<)` and
 `Empty` pattern, for views. I'd like to be able to say that for one
 particular type `{-# complete (:<), Empty  #-}` holds, but since both
 aren't defined in the same module and neither one mentions my type, I'm
 stuck in the same `-Wno-incomplete-patterns` mess I was in before.

 I cant move the pragma to the individual view patterns because in general
 they aren't known to be a complete pattern set.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14422>
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