[GHC] #8221: Type checker hangs

[GHC]

#8221: Type checker hangs
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        Reporter:  maxs                       |            Owner:  dreixel
            Type:  bug                        |           Status:  new
        Priority:  highest                    |        Milestone:  7.8.1
       Component:  Compiler                   |          Version:  7.7
      Resolution:                             |         Keywords:  hangs
Operating System:  Unknown/Multiple           |     Architecture:  arm
 Type of failure:  GHC rejects valid program  |       Difficulty:  Unknown
       Test Case:                             |       Blocked By:
        Blocking:                             |  Related Tickets:
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Comment (by monoidal):

 Here is a smaller testcase. The bug is not related to Typeable.

 File A.hs:

 {{{
 module A where

 import Data.IORef

 data Link a = Link !(IORef (Link a)) | X deriving Eq
 }}}

 File T.hs:

 {{{
 module T where

 import A

 data Located e = L () e deriving Eq
 }}}

 Run `ghc-7.7 -O A.hs` and then `ghc-7.7 T.hs`, the second command should
 hang.

 While investigating this, I also found that compiling this contrived file
 with HEAD and -O hangs, while 7.6.3 succeeds. However, it is probably a
 different issue because deriving is not used:

 {{{
 module M where

 data Link a = Link !(Link a)
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8221#comment:2>
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