[GHC] #10031: coerce can cause compiler to loop

[GHC]

#10031: coerce can cause compiler to loop
-------------------------------------+-------------------------------------
              Reporter:  glguy       |             Owner:
                  Type:  bug         |            Status:  new
              Priority:  normal      |         Milestone:
             Component:  Compiler    |           Version:  7.10.1-rc1
              Keywords:              |  Operating System:  Unknown/Multiple
          Architecture:  x86_64      |   Type of failure:  Compile-time
  (amd64)                            |  crash
             Test Case:              |        Blocked By:
              Blocking:              |   Related Tickets:
Differential Revisions:              |
-------------------------------------+-------------------------------------
 This program causes GHC to loop at compile time

 {{{
 {-# LANGUAGE ScopedTypeVariables #-}
 import Data.Coerce
 coerce' :: Coercible b a => a -> b
 coerce' = coerce (\x -> x :: b) :: forall a b. Coercible b a => a -> b
 }}}

 I encountered this trying to use a similar construction in

 https://github.com/glguy/profunctors/blob/coerce/src/Data/Profunctor/Unsafe.hs

 I'm not absolutely certain about what aspect of this snippet is looping
 the compiler, but it's pretty small.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10031>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler