[GHC] #15499: Panic in occurence analysis phase (?), getRuntimeRep

[GHC]

#15499: Panic in occurence analysis phase (?), getRuntimeRep
-------------------------------------+-------------------------------------
        Reporter:  _deepfire         |                Owner:  RyanGlScott
            Type:  bug               |               Status:  patch
        Priority:  high              |            Milestone:  8.4.4
       Component:  Compiler          |              Version:  8.4.3
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Compile-time      |  Unknown/Multiple
  crash or panic                     |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D5060
       Wiki Page:                    |
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Comment (by Krzysztof Gogolewski <krz.gogolewski@…>):

 In [changeset:"63b6a1d44849c479d2a7cb59211f5c64d133bc62/ghc"
 63b6a1d4/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="63b6a1d44849c479d2a7cb59211f5c64d133bc62"
 Be mindful of GADT tyvar order when desugaring record updates

 Summary:
 After commit ef26182e2014b0a2a029ae466a4b121bf235e4e4,
 the type variable binders in GADT constructor type signatures
 are now quantified in toposorted order, instead of always having
 all the universals before all the existentials. Unfortunately, that
 commit forgot to update some code (which was assuming the latter
 scenario) in `DsExpr` which desugars record updates. This wound
 up being the cause of #15499.

 This patch makes up for lost time by desugaring record updates in
 a way such that the desugared expression applies type arguments to
 the right-hand side constructor in the correct order—that is, the
 order in which they were quantified by the user.

 Test Plan: make test TEST=T15499

 Reviewers: simonpj, bgamari

 Reviewed By: simonpj

 Subscribers: rwbarton, carter

 GHC Trac Issues: #15499

 Differential Revision: https://phabricator.haskell.org/D5060
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15499#comment:8>
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