[GHC] #15716: GHC hangs on default implementation of type family

[GHC]

#15716: GHC hangs on default implementation of type family
-------------------------------------+-------------------------------------
        Reporter:  Heimdell          |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  high              |            Milestone:
       Component:  Compiler          |              Version:  8.4.1
      Resolution:                    |             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:                    |
-------------------------------------+-------------------------------------

Comment (by Heimdell):

 It seems to consume neither any memory during the hang, nor processor
 time.

 `strace` says:
 {{{
 futex(0x24c8440, FUTEX_WAIT_PRIVATE, 0, NULL) = ? ERESTARTSYS (To be
 restarted if SA_RESTART is set)
 --- SIGVTALRM {si_signo=SIGVTALRM, si_code=SI_TIMER, si_timerid=0,
 si_overrun=0, si_value={int=0, ptr=NULL}} ---
 rt_sigreturn({mask=[]})                 = 202
 futex(0x24c8440, FUTEX_WAIT_PRIVATE, 0, NULL) = ? ERESTARTSYS (To be
 restarted if SA_RESTART is set)
 --- SIGVTALRM {si_signo=SIGVTALRM, si_code=SI_TIMER, si_timerid=0,
 si_overrun=0, si_value={int=0, ptr=NULL}} ---
 write(9, "\377\0\0\0\0\0\0\0", 8)       = 8
 rt_sigreturn({mask=[]})                 = 202
 futex(0x24c8440, FUTEX_WAIT_PRIVATE, 0, NULL) = ? ERESTARTSYS (To be
 restarted if SA_RESTART is set)
 --- SIGVTALRM {si_signo=SIGVTALRM, si_code=SI_TIMER, si_timerid=0,
 si_overrun=0, si_value={int=0, ptr=NULL}} ---
 rt_sigreturn({mask=[]})                 = 202
 futex(0x24c8440, FUTEX_WAIT_PRIVATE, 0, NULL) = ? ERESTARTSYS (To be
 restarted if SA_RESTART is set)
 --- SIGVTALRM {si_signo=SIGVTALRM, si_code=SI_TIMER, si_timerid=0,
 si_overrun=0, si_value={int=0, ptr=NULL}} ---
 rt_sigreturn({mask=[]})                 = 202
 futex(0x24c8440, FUTEX_WAIT_PRIVATE, 0, NULL^C) = ? ERESTARTSYS (To be
 restarted if SA_RESTART is set)
 ^Cstrace: Process 13755 detached
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15716#comment:1>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler