[GHC] #14612: unsolved constraints, panic during compilation

[GHC]

#14612: unsolved constraints, panic during compilation
-------------------------------------+-------------------------------------
           Reporter:  msk            |             Owner:  (none)
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.2.2
           Keywords:                 |  Operating System:  Linux
       Architecture:  x86_64         |   Type of failure:  Compile-time
  (amd64)                            |  crash or panic
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
-------------------------------------+-------------------------------------
 Code:
 {{{#!hs
 import Graphics.X11.Xlib

 getWindowRect :: Display -> Window -> IO Rectangle
 getWindowRect dpy w = fmap makeRect (getWindowAttributes dpy w)
 }}}

 Error:
 {{{
 # ghc main.hs
 [1 of 1] Compiling Main             ( main.hs, main.o )
 ghc: panic! (the 'impossible' happened)
   (GHC version 8.0.2 for x86_64-unknown-linux):
         initTc: unsolved constraints
   WC {wc_insol =
         [W] makeRect_a1LX :: t_a1LW[tau:1] (CHoleCan: makeRect)
         [W] getWindowAttributes_a1M2 :: t_a1M1[tau:1] (CHoleCan:
 getWindowAttributes)}

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

 Compiler:
 {{{
 ghc --version
 The Glorious Glasgow Haskell Compilation System, version 8.0.2
 }}}

 Graphics.X11.Xlib from the ArchHaskell package:
 {{{
 haskell-x11 1.8.x0-1
 }}}

 Frankly, I'm just following the request made by the compiler output
 "Please report this as a GHC bug" and have no idea what's going on.
 Hopefully this isn't spurious. Let me know if I can help at all.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14612>
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