[GHC] #11480: UndecidableSuperClasses causes the compiler to spin with UndecidableInstances

[GHC]

#11480: UndecidableSuperClasses causes the compiler to spin with
UndecidableInstances
-------------------------------------+-------------------------------------
        Reporter:  ekmett            |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler (Type    |              Version:  8.0.1-rc1
  checker)                           |             Keywords:  PolyKinds,
      Resolution:                    |  UndecidableSuperClasses
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  GHC rejects       |  Unknown/Multiple
  valid program                      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #10318            |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Comment (by Simon Peyton Jones <simonpj@…>):

 In [changeset:"42c6263f23cf3f00035389637862944e0594bc7a/ghc"
 42c6263f/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="42c6263f23cf3f00035389637862944e0594bc7a"
 Avoid recursive use of immSuperClasses

 In fixing Trac #11480 I had omitted to deal with FunDeps.oclose,
 which was making recursive use of immSuperClasses, and hence
 going into a loop in the recursive case.

 Solution: use transSuperClasses, which takes care not to.
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11480#comment:9>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler