[GHC] #10071: Implement deprecation-warnings for class-methods to non-method transitions

[GHC]

#10071: Implement deprecation-warnings for class-methods to non-method transitions
-------------------------------------+-------------------------------------
        Reporter:  hvr               |                   Owner:
            Type:  feature request   |                  Status:  new
        Priority:  normal            |               Milestone:  7.12.1
       Component:  Compiler          |                 Version:  7.8.4
      Resolution:                    |                Keywords:  AMP
Operating System:  Unknown/Multiple  |            Architecture:
 Type of failure:  None/Unknown      |  Unknown/Multiple
      Blocked By:                    |               Test Case:
 Related Tickets:  #8004, #4384      |                Blocking:
                                     |  Differential Revisions:
-------------------------------------+-------------------------------------

Comment (by ekmett):

 The main purpose of such a feature is to give us the ability to smoothly
 remove redundant class members over a deprecation cycle. (Admittedly,
 perhaps, quite a long deprecation cycle in the case of something like
 `return`!)

 e.g. `(>>)` could be reduced to a top level binding to `(*>)` after a
 period with a warning making it clear that this was coming.

 Other examples of candidates are Traversable's `sequence` and `sequenceA`,
 although there is currently a technical barrier to removing `mapM`
 entirely. This would enable us to eventually reclaim `sequence` for use on
 `Applicative` data types.

 Having the ability to do these things means we can put together future
 proposals for how to move AMP (or FTP) along with reduced breakage.

 I confess to not being terribly concerned about the choice of syntax,
 though. =)

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10071#comment:5>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler