[GHC] #12746: Assertion failed with BuildFlavour = devel2 (one more)

[GHC]

#12746: Assertion failed with  BuildFlavour = devel2 (one more)
-------------------------------------+-------------------------------------
        Reporter:  pacak             |                Owner:  mpickering
            Type:  bug               |               Status:  patch
        Priority:  high              |            Milestone:
       Component:  Compiler          |              Version:  8.0.1
      Resolution:                    |             Keywords:
                                     |  PatternSynonyms
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Compile-time      |  Unknown/Multiple
  crash or panic                     |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D2624
       Wiki Page:                    |
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Comment (by Ben Gamari <ben@…>):

 In [changeset:"23143f60680f78f80762754fe060a3e8c6dc9a01/ghc" 23143f6/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="23143f60680f78f80762754fe060a3e8c6dc9a01"
 Refine ASSERT in buildPatSyn for the nullary case.

 For a nullary pattern synonym we add an extra void argument to the
 matcher in order to preserve laziness. The check in buildPatSyn
 wasn't aware of this special case which was causing the assertion to
 fail.

 Reviewers: austin, simonpj, bgamari

 Reviewed By: simonpj, bgamari

 Subscribers: simonpj, thomie

 Differential Revision: https://phabricator.haskell.org/D2624

 GHC Trac Issues: #12746
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12746#comment:8>
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