[GHC] #15803: Put more info with flag description

[GHC]

#15803: Put more info with flag description
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           Reporter:  simonpj        |             Owner:  (none)
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.6.1
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 In the user manual, consider flag `-fcase-folding`.

 * It appears in [http://downloads.haskell.org/~ghc/master/users-
 guide/flags.html#individual-optimisations this table] where we learn that
 it is implied by `-O`.

 * But if you click on the flag name to
 [http://downloads.haskell.org/~ghc/master/users-guide/using-
 optimisation.html#ghc-flag--fcase-folding get more detail here], we no
 longer see that it's implied by -O.  We just see that it defaults "on"
 which suggests it might be on with -O0.

 The source material, in `using-optimisation.rst` looks like this
 {{{
 .. ghc-flag:: -fcase-folding
     :shortdesc: Enable constant folding in case expressions. Implied by
 :ghc-flag:`-O`.
     :type: dynamic
     :reverse: -fno-case-folding
     :category:

     :default: on

     Allow constant folding in case expressions that scrutinise some
 primops:
     }}}
 I think that in the "more details" page we should definitely display the
 "implied by -O" part, and the "reverse flag".  Could we do that?

 I'm not sure about the "default".  It's bizarre to be implied by -O but
 by-default on!

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15803>
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