[GHC] #11216: RebindableSyntax with pattern guards needs `fail`

[GHC]

#11216: RebindableSyntax with pattern guards needs `fail`
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        Reporter:  goldfire          |                Owner:
            Type:  bug               |               Status:  patch
        Priority:  normal            |            Milestone:  8.2.1
       Component:  Compiler          |              Version:  7.11
      Resolution:                    |             Keywords:
                                     |  RebindableSyntax
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:  T11216,
                                     |  T11216A
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D2896
       Wiki Page:                    |
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Comment (by Ben Gamari <ben@…>):

 In [changeset:"48a5da9ac6abd42e713402bd38612ce6624cac1b/ghc"
 48a5da9a/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="48a5da9ac6abd42e713402bd38612ce6624cac1b"
 rename: Add note describing #11216
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11216#comment:8>
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