[GHC] #11325: Type of hole does not get refined after pattern matching on [GADT] constructors

[GHC]

#11325: Type of hole does not get refined after pattern matching on [GADT]
constructors
-------------------------------------+-------------------------------------
        Reporter:  Iceland_jack      |                Owner:  goldfire
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler (Type    |              Version:  7.11
  checker)                           |
      Resolution:                    |             Keywords:  GADTs
Operating System:  Linux             |         Architecture:  x86
 Type of failure:  Incorrect         |            Test Case:
  warning at compile-time            |
      Blocked By:                    |             Blocking:
 Related Tickets:  #12468            |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------
Changes (by RyanGlScott):

 * related:   => #12468


Comment:

 See #12468, where SPJ argues that the current behavior is not necessarily
 wrong, and proposes that we should instead report something to the effect
 of:

 {{{
     • Found hole: _ :: ty
       ...
     • NB: ty ~ Maybe a
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11325#comment:3>
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