[GHC] #15370: Typed hole panic on GHC 8.6 (tcTyVarDetails)

[GHC]

#15370: Typed hole panic on GHC 8.6 (tcTyVarDetails)
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        Reporter:  RyanGlScott       |                Owner:  Tritlo
            Type:  bug               |               Status:  patch
        Priority:  high              |            Milestone:  8.6.1
       Component:  Compiler (Type    |              Version:  8.4.3
  checker)                           |             Keywords:  TypeInType,
      Resolution:                    |  TypedHoles
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):
       Wiki Page:                    |
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Comment (by Krzysztof Gogolewski <krz.gogolewski@…>):

 In [changeset:"0dc86f6bc454253969dedc31bed477eded4cf82d/ghc"
 0dc86f6b/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="0dc86f6bc454253969dedc31bed477eded4cf82d"
 Clone relevant constraints to avoid side-effects on HoleDests. Fixes
 #15370.

 Summary: When looking for valid hole fits, the constraints relevant
 to the hole may sometimes contain a HoleDest. Previously,
 these were not cloned, which could cause the filling of filled
 coercion hole being, which would cause an assert to fail. This is now
 fixed.

 Test Plan: Regression test included.

 Reviewers: simonpj, bgamari, goldfire

 Reviewed By: simonpj

 Subscribers: rwbarton, thomie, carter

 GHC Trac Issues: #15370

 Differential Revision: https://phabricator.haskell.org/D5004
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15370#comment:13>
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