[GHC] #11371: Bogus in-scope set in substitutions

[GHC]

#11371: Bogus in-scope set in substitutions
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        Reporter:  simonpj           |                Owner:  niteria
            Type:  bug               |               Status:  new
        Priority:  high              |            Milestone:  8.2.1
       Component:  Compiler          |              Version:  7.10.3
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #11360            |  Differential Rev(s):  phab:D1792
       Wiki Page:                    |
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Comment (by Bartosz Nitka <niteria@…>):

 In [changeset:"9d33adb6f352ad4e488067a8756928b3778920e0/ghc"
 9d33adb6/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="9d33adb6f352ad4e488067a8756928b3778920e0"
 Check InScopeSet in substTy and provide substTyUnchecked

 This adds sanity checks to `substTy` that implement:

 > when calling substTy subst ty it should be the case that the in-scope
 > set in the substitution is a superset of
 > * The free vars of the range of the substitution
 > * The free vars of ty minus the domain of the substitution

 and replaces violators with unchecked version. The violators were found
 by running the GHC test suite.

 This ensures that I can work on this incrementally and that what I fix
 won't
 be undone by some other change.

 It also includes a couple of fixes that I've already done.

 Test Plan: ./validate

 Reviewers: simonmar, goldfire, simonpj, austin, bgamari

 Reviewed By: simonpj, bgamari

 Subscribers: thomie

 Differential Revision: https://phabricator.haskell.org/D1792

 GHC Trac Issues: #11371
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11371#comment:5>
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