[GHC] #11345: Template Haskell's handling of infix GADT constructors is broken

[GHC]

#11345: Template Haskell's handling of infix GADT constructors is broken
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        Reporter:  RyanGlScott       |                Owner:  RyanGlScott
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Template Haskell  |              Version:  8.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Incorrect result  |  Unknown/Multiple
  at runtime                         |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by RyanGlScott):

 Hm... I might have been a bit too optimistic in my timeframe estimate.

 I ran into a very tricky stumbling block when trying to implement this.
 Namely, what happens when you try to splice an infix `GadtC` into source
 code in `Convert.hs`? Unlike `InfixC`, the infixity of a GADT constructor
 depends on the presence of a user-supplied fixity declaration. But AFAIK,
 there's no way to look up what things have fixity declarations in `CvtM`.

 I suppose you could just ignore the declaration fixity field of `GadtC`
 during splicing. But then if you don't also splice in a corresponding
 fixity declaration, you might actually end up with a non-infix GADT
 constructor in the end, even if you marked it otherwise.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11345#comment:4>
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