[GHC] #10820: Provide a way to detect what extensions are enabled via TH

[GHC]

#10820: Provide a way to detect what extensions are enabled via TH
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        Reporter:  spinda            |                Owner:  spinda
            Type:  feature request   |               Status:  closed
        Priority:  normal            |            Milestone:  8.0.1
       Component:  Template Haskell  |              Version:  7.10.2
      Resolution:  fixed             |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:  th/T18020.hs
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D1200
       Wiki Page:                    |
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Description changed by bgamari:

Old description:

> This would be helpful for providing users with intuitive/explanatory
> error messages if generated code relies on an extension that the user may
> not have enabled.
>
> Sample specification, to get things started:
>
> {{{
> enabledExts :: Q [Extension]
> isExtEnabled :: Extension -> Q Bool
> data Extension = LiberalTypeSynonyms | RankNTypes | ...
>     -- mirroring ExtensionFlag in DynFlags
> }}}
>
> See #10819 for an example case where this could be of use.

New description:

 This would be helpful for providing users with intuitive/explanatory error
 messages if generated code relies on an extension that the user may not
 have enabled.

 Sample specification, to get things started:

 {{{#!hs
 enabledExts :: Q [Extension]
 isExtEnabled :: Extension -> Q Bool
 data Extension = LiberalTypeSynonyms | RankNTypes | ...
     -- mirroring ExtensionFlag in DynFlags
 }}}

 See #10819 for an example case where this could be of use.

--

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10820#comment:9>
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