[GHC] #14751: GHC wrongly warns of incomplete pattern matches when using pattern synonyms.

[GHC]

#14751: GHC wrongly warns of incomplete pattern matches when using pattern
synonyms.
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        Reporter:  vanessamchale     |                Owner:  (none)
            Type:  bug               |               Status:  closed
        Priority:  low               |            Milestone:
       Component:  Compiler          |              Version:  8.4.1-alpha1
      Resolution:  duplicate         |             Keywords:
Operating System:  Linux             |         Architecture:  x86_64
 Type of failure:  GHC rejects       |  (amd64)
  valid program                      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Changes (by nomeata):

 * status:  new => closed
 * resolution:   => duplicate


Comment:

 This is expected behaviour: Because pattern synonyms can do arbitrary
 computations, the compiler does not even attempt to detect when they are
 complete.

 You can specify
 {{{
 {-# COMPLETE V #-}
 }}}
 to declare that the `V` pattern is complete.

 Also see #8779.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14751#comment:1>
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