[GHC] #9515: Deprecate -XExplicitForAll

[GHC]

#9515: Deprecate -XExplicitForAll
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              Reporter:  dfeuer      |            Owner:
                  Type:  feature     |           Status:  new
  request                            |        Milestone:
              Priority:  normal      |          Version:  7.8.3
             Component:  Compiler    |         Keywords:
            Resolution:              |     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 dfeuer):

 I've gone over practically the entire GHC source tree (I ran out of time
 before I could look at the last few validation tests files).


 === Good News ===

 Very few files explicitly use `ExplicitForAll`.

 Of all the files that use `ExplicitForAll` or anything that implies it,
 only one, a file in the `fibon` benchmark suite, would need minor changes
 to work with `ScopedTypeVariables`.

 === Bad News ===

 Lots and lots of files use extensions that imply `ExplicitForAll` and
 don't use `ScopedTypeVariables`.

 I don't personally see an obvious way to warn when something ''implying''
 `ExplicitForAll` is used without `ScopedTypeVariables`, although someone
 else may be able to figure something out.

 === Question ===

 Should we just bite the bullet and just make everything that currently
 implies `ExplicitForAll` imply `ScopedTypeVariables` instead? It seems,
 contrary to my earlier fears, that this is likely to break very little
 real code.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9515#comment:4>
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