[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:                    |
-------------------------------------+-------------------------------------
Changes (by mpickering):

 * status:  new => patch
 * differential:   => Phab:D2624


Comment:

 The ASSERT was slightly wrong as there is a special case where a `Void#`
 argument is added to the matching continuation to ensure laziness for a
 nullary pattern synonym. The fix is to check whether the number of
 arguments is 0 and if so check wether the only argument to the matcher is
 `Void#`.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12746#comment:7>
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