[GHC] #9242: Implement {-# OVERLAPPABLE #-} and {-# INCOHERENT #-} pragmas

[GHC]

#9242: Implement {-# OVERLAPPABLE #-} and {-# INCOHERENT #-} pragmas
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              Reporter:  simonpj     |            Owner:  diatchki
                  Type:  feature     |           Status:  closed
  request                            |        Milestone:
              Priority:  normal      |          Version:  7.8.2
             Component:  Compiler    |         Keywords:
            Resolution:  fixed       |     Architecture:  Unknown/Multiple
      Operating System:              |       Difficulty:  Unknown
  Unknown/Multiple                   |       Blocked By:
       Type of failure:              |  Related Tickets:
  None/Unknown                       |
             Test Case:              |
              Blocking:              |
Differential Revisions:              |
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Comment (by Herbert Valerio Riedel <hvr@…>):

 In [changeset:"cbb20ab2c3222da75625bcf41f8ff67a7e9ba5f7/ghc"]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="cbb20ab2c3222da75625bcf41f8ff67a7e9ba5f7"
 Drop deprecated `OverlappingInstances` from base

 With #9242 the `OverlappingInstances` extension got deprecated, this
 commit adapts the only two remaining places in `base` where it was still
 used.

 Starting with this commit, the `Typeable (s t)` instance (which seemingly
 was the motivation for using `OverlappingInstances` in the first place
 when `Typeable` was neither polykinded nor auto-derived-only, see also
 commit ce3fd0e02826367e6134a3362d8d37aa114236f5 which introduced
 overlapping instances) does no longer allow overlapping instances, and
 there doesn't seem to be any good reason to keep allowing overlapping
 instance now.

 This also removes redundant `LANGUAGE`/`OPTIONS_GHC` pragmas from
 `Data.Typeable` and refactors the language pragmas into more uniform
 single-line pragmas.

 Reviewed By: austin

 Differential Revision: https://phabricator.haskell.org/D377
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9242#comment:38>
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