[GHC] #9840: Permit empty closed type families

[GHC]

#9840: Permit empty closed type families
-------------------------------------+-------------------------------------
        Reporter:  adamgundry        |                   Owner:
            Type:  feature request   |                  Status:  merge
        Priority:  normal            |               Milestone:
       Component:  Compiler (Type    |                 Version:  7.8.3
  checker)                           |                Keywords:
      Resolution:                    |            Architecture:
Operating System:  Unknown/Multiple  |  Unknown/Multiple
 Type of failure:  None/Unknown      |               Test Case:  indexed-
      Blocked By:                    |  types/should_compile/T9840
 Related Tickets:  #8028             |                Blocking:
                                     |  Differential Revisions:  Phab:D841
-------------------------------------+-------------------------------------

Comment (by thoughtpolice):

 So, this one visibly changes the API and requires a Haddock update, so I'm
 pretty inclined to leave it as is and not merge. Adam, is this one
 critical, or can it be worked around/backported reasonably?

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9840#comment:11>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler