[GHC] #9778: Namespace collision detection for promoted types

[GHC]

#9778: Namespace collision detection for promoted types
-------------------------------------+-------------------------------------
              Reporter:  crockeea    |            Owner:  carlostome
                  Type:  feature     |           Status:  new
  request                            |        Milestone:
              Priority:  normal      |          Version:  7.8.3
             Component:  Compiler    |         Keywords:  newcomer
            Resolution:              |     Architecture:  Unknown/Multiple
      Operating System:              |       Difficulty:  Unknown
  Unknown/Multiple                   |       Blocked By:
       Type of failure:              |  Related Tickets:
  None/Unknown                       |
             Test Case:  T9778       |
              Blocking:              |
Differential Revisions:  Phab:D534   |
-------------------------------------+-------------------------------------
Changes (by carlostome):

 * testcase:   => T9778
 * differential:   => Phab:D534


Comment:

 I added this warning flag and updated the documentation according to it.
 The new flag is documented as follows:

 ----
 -fwarn-unticked-promoted-constructors:

     Warn if a promoted data constructor is used without a tick preceding
 it's name.

     For example:

 {{{
     data Nat = Succ Nat | Zero

     data Vec n s where
       Nil  :: Vec Zero a
       Cons :: a -> Vec n a -> Vec (Succ n) a
 }}}

     This program will raise two warnings because Zero and Succ are not
 written as 'Zero and 'Succ.

     This warning is off by default.


 ----

 If anybody thinks this can be explained better, all suggestions are
 welcomed!

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9778#comment:13>
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