[GHC] #14105: ApplicativeDo causes GHC panic on irrefutable list pattern match

[GHC]

#14105: ApplicativeDo causes GHC panic on irrefutable list pattern match
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           Reporter:  BoteboTsebo    |             Owner:  (none)
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.2.1
           Keywords:  ApplicativeDo  |  Operating System:  Unknown/Multiple
       Architecture:  x86_64         |   Type of failure:  None/Unknown
  (amd64)                            |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 So this just happened:

 {{{#!hs
 {-# language ApplicativeDo #-}
 module Main where

 main :: IO ()
 main = do
   [_] <- pure []
   pure ()
 }}}

 Compiling (under Stack) with `stack exec -- ghc --make src/Main.hs` yields
 {{{
 [1 of 1] Compiling Main             ( src/Main.hs, src/Main.o )
 ghc: panic! (the 'impossible' happened)
   (GHC version 8.2.1 for x86_64-unknown-linux):
         isStrictPattern

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

 This does not happen on GHC-8.0.2. It does not happen when `ApplicativeDo`
 is not activated. It also does not happen when the pattern match line is
 changed to
 {{{#!hs
   [] <- pure []
 }}}


 For completeness, the compiler used by `stack` is that which comes with
 `nightly-2017-08-10`. I am on Linux x64 (Ubuntu).

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14105>
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