[GHC] #13267: Constraint synonym instances

[GHC]

#13267: Constraint synonym instances
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        Reporter:  ezyang            |                Owner:  (none)
            Type:  bug               |               Status:  closed
        Priority:  normal            |            Milestone:  8.2.1
       Component:  Compiler (Type    |              Version:  8.1
  checker)                           |
      Resolution:  fixed             |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  GHC accepts       |            Test Case:
  invalid program                    |  polykinds/T13267
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by niteria):

 I'd like to just note that https://github.com/niteria/dual-
 tree/blob/master/test/Test.hs now fails to build with:

 {{{
 test/Test.hs:55:19: error:
     • Illegal instance for a type synonym
       A class instance must be for a class
     • In the stand-alone deriving instance for ‘Typeable1 Sum’
    |
 55 | deriving instance Typeable1 X.Sum
    |                   ^^^^^^^^^^^^^^^

 test/Test.hs:56:19: error:
     • Illegal instance for a type synonym
       A class instance must be for a class
     • In the stand-alone deriving instance for ‘Typeable1 Product’
    |
 56 | deriving instance Typeable1 X.Product
    |                   ^^^^^^^^^^^^^^^^^^^
 }}}

 I will attach a smaller example.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13267#comment:10>
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