[GHC] #13021: Inaccessible RHS warning is confusing for users

[GHC]

#13021: Inaccessible RHS warning is confusing for users
-------------------------------------+-------------------------------------
        Reporter:  mpickering        |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.1
      Resolution:                    |             Keywords:
                                     |  PatternMatchWarnings
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by mpickering):

 It is easy to trigger cases like this with `COMPLETE` signatures as they
 are currently designed.

 For example,

 {{{
 data T = A | B | C

 {-# COMPLETE B #-}

 foo :: T -> ()
 foo A = ()
 foo B = ()
 }}}

 Then the first match is reported as having an inaccessible RHS.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13021#comment:5>
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