[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:
            Type:  feature request   |                  Status:  new
        Priority:  normal            |               Milestone:  7.12.1
       Component:  Template Haskell  |                 Version:  7.10.2
      Resolution:                    |                Keywords:
Operating System:  Unknown/Multiple  |            Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |               Test Case:
      Blocked By:                    |                Blocking:
 Related Tickets:                    |  Differential Revisions:
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Changes (by goldfire):

 * milestone:   => 7.12.1


Comment:

 I've wanted this, too. It should be able to happen by 7.12.

 But, what data type to use for the extensions? Would it work to have
 `template-haskell` depend on `Cabal` to pull the extension type from
 there? My guess: no. Would it work to have `template-haskell` depend on
 `ghc` and pull the type from `DynFlags`? My guess: yes.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10820#comment:2>
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