[GHC] #12014: Make it possible to deprecate a method instantiation of a typeclass instance

[GHC]

#12014: Make it possible to deprecate a method instantiation of a typeclass
instance
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        Reporter:  niteria           |                Owner:
            Type:  feature request   |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by simonpj):

 Replying to [comment:3 simonmar]:
 > Deprecating the whole instance should be possible though, right?  We
 could emit the deprecation message whenever the typechecker uses the
 instance.

 That would be quite possible, yes, and more robust.

 The challenge then is the user interface.  Possibly
 {{{
 instance Eq Foo where
   {-# DEPRECATED "Don't use the Eq instance of Foo" #-}
 }}}
 This would be fantastic if you want to remove the Eq instance.

 Not to hard to do if someone wants to try.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12014#comment:4>
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