[GHC] #14772: Keep Role Annotations in the renamed syntax tree

6 Feb 2018

      #14772: Keep Role Annotations in the renamed syntax tree
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           Reporter:  lazac          |             Owner:  (none)
               Type:  feature        |            Status:  new
  request                            |
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.2.2
  (Type checker)                     |
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 Currently role annotations are present in the parsed representation, but
 missing from the renamed version of the syntax tree. GHC should keep them
 instead. I found no evidence that this would be intended, we even have
 `rnRoleAnnots` that should return the renamed annotations.

 Keeping role annotations would help tooling to be consistent. For example,
 renaming the datatype should also rename its occurrence in the role
 annotation.

 Minimal example:

 A.hs
 {{{#!hs
 module A where
 import B
 data A x = A B
 }}}

 B.hs
 {{{#!hs
 module B where
 import {-# SOURCE #-} A
 data B = B (A ())
 }}}

 A.hs-boot
 {{{#!hs
 {-# LANGUAGE RoleAnnotations #-}
 module A where
 type role A phantom -- the role annotation is needed here
 data A x
 }}}

 When inspecting the representation using the GHC API, the role is present
 in the parsed representation:

 {{{
 module A where  -- Parsed module
 type role A phantom
 data A x
 }}}

 But missing from the renamed one:

 {{{
 (data A x, [import (implicit) Prelude], Nothing, Nothing) -- RenamedSource
 }}}

-- 
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14772
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