[GHC] #9066: Template Haskell cannot splice an infix declaration for a data constructor

[GHC]

#9066: Template Haskell cannot splice an infix declaration for a data constructor
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              Reporter:  goldfire    |            Owner:  goldfire
                  Type:  bug         |           Status:  new
              Priority:  normal      |        Milestone:
             Component:  Template    |          Version:  7.8.2
  Haskell                            |         Keywords:
            Resolution:              |     Architecture:  Unknown/Multiple
      Operating System:              |       Difficulty:  Unknown
  Unknown/Multiple                   |       Blocked By:
       Type of failure:              |  Related Tickets:
  None/Unknown                       |
             Test Case:              |
              Blocking:              |
Differential Revisions:              |
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Comment (by goldfire):

 Harrumph. In that second case, {{{[d| infix 5 `Foo` |]}}} produces an
 `Exact` `RdrName` for `Foo` that names a ''data'' constructor, not a
 ''type'' constructor, even when only the type constructor is in scope.
 Then, according to `Note [dataTcOccs and Exact Names]` in !RnEnv, the
 `Exact` `RdrName`s are trusted to have the right namespace and, so a naive
 fix for this bug fails the `Foo` case.

 There are two possible ways forward that I see:
 1. Don't trust `Exact` `RdrName`s in `dataTcOccs`. That is, when we have
 an `Exact` constructor name, also look for the type with same spelling.
 2. Duplicate the `dataTcOccs` logic in !DsMeta.

 I favor (2), because code that consumes the TH AST will want the
 `TH.Name`s to have the right namespaces. It's really a bug that the fixity
 declaration above refers to a data constructor `Foo`.

 Going to implement (2).

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9066#comment:2>
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