[GHC] #15562: `-XStrict -XNoStrict` is not neutral

[GHC]

#15562: `-XStrict -XNoStrict` is not neutral
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           Reporter:  hvr            |             Owner:  (none)
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:  8.6.1
          Component:  Compiler       |           Version:  8.4.3
           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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 I assumed we already had a ticket about this, but it appears we have not.

 I'm not saying this is a necessarily a bug in the implementation; but we
 should make sure this is properly documented in the user's guide, and
 ideally justify why it's done this way rather than the alternatives:


 As described in StrictPragma,

 > `Strict` implies `StrictData`

 Currently however the inverse case does not hold, i.e. `NoStrict` does
 *not* imply `NoStrictData`




 This has the surprising property (assuming these were left-most flags on
 the CLI) that

 - `-XStrict -XNoStrict` == `-XStrictData`

 - `-XStrictData -XNoStrict` == `-XStrictData`



 However, if `-XNoStrict` was to naively imply `-XNoStrictData`, we'd have
 the properties


 - `-XStrict -XNoStrict` == *id*

 - `-XStrictData -XNoStrict` == *id*


 This might be a bit less confusing; another variant would be


 - `-XStrict -XNoStrict` == *id*

 - `-XStrictData -XNoStrict` == `-XStrictData`


 Btw, I'm not sure what the following means:

 - `-XStrict -XNoStrictData` == ?

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15562>
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