[GHC] #14339: GHC 8.2.1 regression when combining GND with TypeError (solveDerivEqns: probable loop)

[GHC]

#14339: GHC 8.2.1 regression when combining GND with TypeError (solveDerivEqns:
probable loop)
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        Reporter:  RyanGlScott       |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  high              |            Milestone:  8.4.1
       Component:  Compiler (Type    |              Version:  8.2.1
  checker)                           |             Keywords:  deriving,
      Resolution:                    |  CustomTypeErrors
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 Simon Peyton Jones <simonpj@…>):

 In [changeset:"13fdca3d174ff15ac347c5db78370f457a3013ee/ghc"
 13fdca3d/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="13fdca3d174ff15ac347c5db78370f457a3013ee"
 Add a missing zonk in TcDerivInfer.simplifyDeriv

 I'm astonished that anything worked without this!

 Fixes Trac #14339
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14339#comment:3>
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