[GHC] #8757: Disallow local pattern synonym declarations

[GHC]

#8757: Disallow local pattern synonym declarations
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        Reporter:  cactus            |            Owner:  cactus
            Type:  bug               |           Status:  new
        Priority:  normal            |        Milestone:
       Component:  Compiler (Type    |          Version:  7.8.1-rc1
  checker)                           |         Keywords:
      Resolution:                    |     Architecture:  Unknown/Multiple
Operating System:  Unknown/Multiple  |       Difficulty:  Easy (less than 1
 Type of failure:  GHC accepts       |  hour)
  invalid program                    |       Blocked By:
       Test Case:                    |  Related Tickets:
        Blocking:  8749              |
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Comment (by Dr. ERDI Gergo <gergo@…>):

 In [changeset:"e0a55415545074bc7a757462624079f54f7785e2/ghc"]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="e0a55415545074bc7a757462624079f54f7785e2"
 Issue an error for pattern synonyms defined in a local scope (#8757)

 This also fixes the internal crash when using pattern synonyms
 in GHCi (#8749)
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8757#comment:2>
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