[GHC] #14102: panic! (the 'impossible' happened)

[GHC]

#14102: panic! (the 'impossible' happened)
-------------------------------------+-------------------------------------
        Reporter:  pmckelvy          |                Owner:  (none)
            Type:  bug               |               Status:  closed
        Priority:  normal            |            Milestone:  8.2.1
       Component:  Compiler          |              Version:  8.0.2
      Resolution:  fixed             |             Keywords:
Operating System:  MacOS X           |         Architecture:  x86_64
 Type of failure:  Compile-time      |  (amd64)
  crash or panic                     |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------
Changes (by bgamari):

 * status:  new => closed
 * resolution:   => fixed
 * milestone:   => 8.2.1


Old description:

> (GHC version 8.0.2 for x86_64-apple-darwin):
>         initTc: unsolved constraints
>   WC {wc_insol = [W] action_a1Ei :: t_a1Eh[tau:1] (CHoleCan: action)}
>

> ******* code ********
> import Data.Char
> import Data.List
>
> data InvoiceStruct = InvoiceStruct
>     {   total :: Int
>     ,   shippedItemCount :: Int
>     } deriving (Show)
>
> invoice :: InvoiceStruct -> String -> Int -> InvoiceStruct
> invoice i comp val = (action) i[total] val

New description:

 {{{
   (GHC version 8.0.2 for x86_64-apple-darwin):
         initTc: unsolved constraints
   WC {wc_insol = [W] action_a1Ei :: t_a1Eh[tau:1] (CHoleCan: action)}
 }}}

 Code:
 {{{#!hs
 import Data.Char
 import Data.List

 data InvoiceStruct = InvoiceStruct
     {   total :: Int
     ,   shippedItemCount :: Int
     } deriving (Show)

 invoice :: InvoiceStruct -> String -> Int -> InvoiceStruct
 invoice i comp val = (action) i[total] val
 }}}

--

Comment:

 Thanks for your report! This fails with the expected errors under 8.2.1,
 {{{

 hi.hs:1:1: error:
     The IO action ‘main’ is not defined in module ‘Main’
   |
 1 | import Data.Char
   | ^

 hi.hs:10:23: error:
     Variable not in scope:
       action
         :: Main.InvoiceStruct
            -> [Main.InvoiceStruct -> Int] -> Int -> Main.InvoiceStruct
    |
 10 | invoice i comp val = (action) i[total] val
    |                       ^^^^^^
 }}}

 It's not entirely clear what fixed this but it's unlikely that we will
 release a 8.0.3 so I'm going to close this for now.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14102#comment:1>
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