[GHC] #14777: panic when using a function defined in terms of `error`

[GHC]

#14777: panic when using a function defined in terms of `error`
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        Reporter:  zilinc            |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.2.2
      Resolution:                    |             Keywords:
Operating System:  Linux             |         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 sighingnow):

 I have create a self-contained minimal case (still have several files but
 only depends on base, mtl and containers) that can trigger this panic.

 I **can** reproduce this panic with ghc-8.2.1 (nightly-2017-11-24) and
 ghc-8.2.2 (lts-10.3/lts-10.4) but **cannot** with ghc-8.4.1 and ghc-head.
 Maybe it has already been fixed. I also have test with with ghc-8.0.1
 (lts-9.4) but also failed to trigger the panic with this minimal case.

 Step to reproduce with ghc-8.2.2: unzip and enter `src`, then

 {{{
 stack exec --resolver=lts-10.4 -- ghc Cogent.Desugar -fforce-recomp  -O2
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14777#comment:14>
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