[GHC] #12819: Pattern synonym signatures are not validity-checked

[GHC]

#12819: Pattern synonym signatures are not validity-checked
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        Reporter:  goldfire          |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler (Type    |              Version:  8.1
  checker)                           |
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  GHC accepts       |  Unknown/Multiple
  invalid program                    |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by Ben Gamari <ben@…>):

 In [changeset:"8906e7b79a585039712034d9e88ca49f3cea6554/ghc"
 8906e7b7/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="8906e7b79a585039712034d9e88ca49f3cea6554"
 Reshuffle levity polymorphism checks.

 Previously, GHC checked for bad levity polymorphism to the left of all
 arrows in data constructors. This was wrong, as reported in #12911
 (where an example is also shown). The solution is to check each
 individual argument for bad levity polymorphism.  Thus the check has
 been moved from TcValidity to TcTyClsDecls.

 A similar situation exists with pattern synonyms, also fixed here.

 This patch also nabs #12819 while I was in town.

 Test cases: typecheck/should_compile/T12911, patsyn/should_fail/T12819

 Test Plan: ./validate

 Reviewers: simonpj, austin, bgamari

 Reviewed By: bgamari

 Subscribers: thomie

 Differential Revision: https://phabricator.haskell.org/D2783

 GHC Trac Issues: #12819, #12911
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12819#comment:1>
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