[GHC] #14253: Pattern match checker mistakenly concludes pattern match on pattern synonym is unreachable

[GHC]

#14253: Pattern match checker mistakenly concludes pattern match on pattern synonym
is unreachable
-------------------------------------+-------------------------------------
        Reporter:  bgamari           |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  high              |            Milestone:  8.4.1
       Component:  Compiler          |              Version:  8.2.1
      Resolution:                    |             Keywords:
                                     |  PatternSynonyms,
                                     |  PatternMatchWarnings
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  GHC rejects       |  Unknown/Multiple
  valid program                      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #11984, #14098    |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Comment (by Ben Gamari <ben@…>):

 In [changeset:"acd346e3fad4d138cd8f421bb84ec6a1b357e326/ghc"
 acd346e3/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="acd346e3fad4d138cd8f421bb84ec6a1b357e326"
 testsuite: Add testcase for #14253

 Reviewers: austin

 Subscribers: rwbarton, thomie

 Differential Revision: https://phabricator.haskell.org/D3997
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14253#comment:12>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler