[GHC] #12404: Document version availability for each language extension

[GHC]

#12404: Document version availability for each language extension
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           Reporter:  dfeuer         |             Owner:
               Type:  feature        |            Status:  new
  request                            |
           Priority:  normal         |         Milestone:  8.2.1
          Component:  Documentation  |           Version:  8.0.1
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  Documentation
  Unknown/Multiple                   |  bug
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 A certain amount of "historical" information about language extensions is
 of sufficient practical utility to deserve a place in the GHC
 documentation. I believe that the documentation for each language
 extension should include

 1. The GHC version in which it first appeared.

 2. Any major changes that have been made to the extension since the
 previous major-major version. For example, the GHC 8.x.x documentation for
 any given language extension should include any major changes to it since
 7.0.1.

 At present, the only way I see to get this information is to dig through
 previous versions of the documentation and change logs, which is rather
 inefficient.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12404>
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