[GHC] #11524: Something is amiss with quantification in pattern synonym type signatures

[GHC]

#11524: Something is amiss with quantification in pattern synonym type signatures
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        Reporter:  bgamari           |                Owner:
            Type:  bug               |               Status:  patch
        Priority:  high              |            Milestone:  8.0.1
       Component:  Compiler (Type    |              Version:  8.0.1-rc1
  checker)                           |             Keywords:
      Resolution:                    |  PatternSynonyms
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  GHC rejects       |  Unknown/Multiple
  valid program                      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D1879
       Wiki Page:                    |
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Comment (by Bartosz Nitka <niteria@…>):

 In [changeset:"07ed24132ebe62aab15f14a655506decdf252ff9/ghc"
 07ed2413/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="07ed24132ebe62aab15f14a655506decdf252ff9"
 Use a correct substitution in tcCheckPatSynDecl

 The `substTheta` call didn't have the free variables of the
 `prov_theta` in the `in_scope` set. It should be enough to add
 `univ_tvs`, as all the `ex_tvs` are already in the domain of
 the substitution.

 Test Plan: added a testcase

 Reviewers: simonpj, bgamari, goldfire, austin

 Reviewed By: simonpj, bgamari

 Subscribers: thomie

 Differential Revision: https://phabricator.haskell.org/D1879

 GHC Trac Issues: #11524
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11524#comment:7>
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