[GHC] #12788: While using Data.Aeson.TH, "Irrefutable pattern failed for pattern sel_id : _"

[GHC]

#12788: While using Data.Aeson.TH, "Irrefutable pattern failed for pattern sel_id :
_"
-------------------------------------+-------------------------------------
           Reporter:  jchia          |             Owner:
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.0.1
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
-------------------------------------+-------------------------------------
 I got the following error compiling simple source file Bad.hs. The bug is
 likely related to TH as the crash vanishes without the TH line.

 $ stack ghc -- -c Bad.hs
 Run from outside a project, using implicit global project config
 Using resolver: lts-7.5 from implicit global project's config file:
 /home/jchia/.stack/global-project/stack.yaml
 ghc: panic! (the 'impossible' happened)
   (GHC version 8.0.1 for x86_64-unknown-linux):
         compiler/typecheck/TcExpr.hs:798:15-35: Irrefutable pattern failed
 for pattern sel_id : _


 Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12788>
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