[GHC] #14846: Renamer hangs (because of -XInstanceSigs?)

[GHC]

#14846: Renamer hangs (because of -XInstanceSigs?)
-------------------------------------+-------------------------------------
        Reporter:  Iceland_jack      |                Owner:  goldfire
            Type:  bug               |               Status:  new
        Priority:  highest           |            Milestone:  8.6.1
       Component:  Compiler          |              Version:  8.5
      Resolution:                    |             Keywords:  InstanceSigs
                                     |  TypeInType
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
                                     |  polykinds/T14846
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------
Changes (by simonpj):

 * owner:  (none) => goldfire
 * testcase:   => polykinds/T14846
 * priority:  normal => highest
 * milestone:   => 8.6.1


Comment:

 Fixed by
 {{{
 commit e99fdf775540440c1c58dc5ade3c5984dc49246f
 Author: Simon Peyton Jones <simonpj at microsoft.com>
 Date:   Mon Feb 26 17:44:55 2018 +0000

     Fix a nasty bug in the pure unifier

     The pure unifier was building an infinite type, through a defective
     occurs check.  So GHC went into an infinite loop.

     Reason: we were neglecting the 'kco' part of the type, which
     'unify_ty' maintains.  Yikes.

     The fix is easy.  I refactored a bit to make it harder to
     go wrong in future.


 >---------------------------------------------------------------

 e99fdf775540440c1c58dc5ade3c5984dc49246f
  compiler/types/Unify.hs                 | 59
 ++++++++++++++++++---------------
  testsuite/tests/polykinds/T14846.hs     | 39 ++++++++++++++++++++++
  testsuite/tests/polykinds/T14846.stderr | 43 ++++++++++++++++++++++++
  testsuite/tests/polykinds/all.T         |  1 +
  4 files changed, 116 insertions(+), 26 deletions(-)
 }}}
 Richard, can you just check my work?  I'll leave the ticket open, but
 assign to you.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14846#comment:8>
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