[GHC] #13292: panic! (the 'impossible' happened): corePrepPgm

[GHC]

#13292: panic! (the 'impossible' happened): corePrepPgm
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           Reporter:  jeiea           |             Owner:  (none)
               Type:  bug             |            Status:  new
           Priority:  normal          |         Milestone:
          Component:  Compiler        |           Version:  8.0.2
           Keywords:                  |  Operating System:  Windows
       Architecture:  x86_64 (amd64)  |   Type of failure:  None/Unknown
          Test Case:                  |        Blocked By:
           Blocking:                  |   Related Tickets:
Differential Rev(s):                  |         Wiki Page:
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 It doesn't seem like a serious problem, but I report it anyway.

 With stack's project template, I just removed `main` and `someFunc`'s type
 signature and changed `someFunc`'s definition to `return ()`.
 `stack build` worked well, but `stack repl` emitted this error message.

 {{{
 D:\ghc-corePrepPgm\app\Main.hs:6:1: warning: [-Wdeferred-type-errors]
     • Couldn't match type ‘ghc-prim-0.5.0.0:GHC.Prim.Any’ with ‘IO’
       Expected type: IO ()
         Actual type: ghc-prim-0.5.0.0:GHC.Prim.Any ()
     • In the expression: main
       When checking the type of the IO action ‘main’
 ghc.EXE: panic! (the 'impossible' happened)
   (GHC version 8.0.2 for x86_64-unknown-mingw32):
         corePrepPgm
   [False] cobox_r1bo = typeError
                          @ 'VoidRep
                          @ (Any :: (* -> *)) ~# (IO :: (* -> *))
                          "D:\\ghc-corePrepPgm\\app\\Main.hs:6:1: error:\n\
                          \    \\226\\128\\162 Couldn't match type
 \\226\\128\\152ghc-prim-0.5.0.0:GHC.Prim.Any\\226\\128\\153 with
 \\226\\128\\152IO\\226\\128\\153\n\
                          \      Expected type: IO ()\n\
                          \        Actual type: ghc-
 prim-0.5.0.0:GHC.Prim.Any ()\n\
                          \    \\226\\128\\162 In the expression: main\n\
                          \      When checking the type of the IO action
 \\226\\128\\152main\\226\\128\\153\n\
                          \(deferred type error)"#

 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/13292>
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