[GHC] #8488: Annotations should not distinguish type and value

[GHC]

#8488: Annotations should not distinguish type and value
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        Reporter:  simonpj           |            Owner:  errge
            Type:  bug               |           Status:  new
        Priority:  normal            |        Milestone:
       Component:  Compiler          |          Version:  7.6.3
      Resolution:                    |         Keywords:
Operating System:  Unknown/Multiple  |     Architecture:  Unknown/Multiple
 Type of failure:  None/Unknown      |       Difficulty:  Unknown
       Test Case:                    |       Blocked By:
        Blocking:                    |  Related Tickets:
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Comment (by errge):

 I looked into this today, but I got stuck.

 The issue is two fold.

 When doing the `HsDecls` change things almost work out, except for
 prettyprinting, because the current ppr code looks like this:

 {{{
 pprAnnProvenance (ValueAnnProvenance name) = ptext (sLit "ANN") <+> ppr
 name
 pprAnnProvenance (TypeAnnProvenance name)  = ptext (sLit "ANN type") <+>
 ppr name
 }}}

 So we use `ValueAnnProvenance` vs `TypeAnnProvenance` to decide if we have
 to print the type keyword after ANN.  I tried to add HasOccName constraint
 at the pretty printer (because for an OccName we know the namespace), but
 that gets out of hand very quickly, since everywhere we just assume
 OutputableBndr now.  And I was unsure at that point if it's feasible or
 not to add everywhere (`HsExpr`, `HsDecls`, etc.)  HasOccName besides
 OutputableBndr.

 The another issue is on the template haskell side.  Template Haskell
 `OccName` is just a `String`, not a `(String, NameSpace)` (maybe I should
 fix that, btw?).  To compensate this mistake we have some heuristics in
 `TcSplice` to convert TH names to compiler names.  Unfortunately this
 means that after the proposed change if the user has `data X = X`, it
 would be very hard for the user to put an annotation on the type and on
 the constructor both.  They would have to resort to `NameG`s which are a
 bit hard to create and not straightforward at all.

 How should I go forward with this issues?

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8488#comment:3>
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