[GHC] #15784: :doc shouldn't report <has no documentation> for a data constructor when it can show docs for the type constructor of the same name and type

[GHC]

#15784: :doc shouldn't report <has no documentation> for a data constructor when it
can show docs for the type constructor of the same name and type
-------------------------------------+-------------------------------------
           Reporter:  sjakobi        |             Owner:  (none)
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  GHCi           |           Version:  8.6.1
           Keywords:  newcomer       |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  Poor/confusing
  Unknown/Multiple                   |  error message
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
-------------------------------------+-------------------------------------
 {{{
 λ import Data.Monoid
 λ :doc Sum
 <has no documentation>

  Monoid under addition.

  >>> getSum (Sum 1 <> Sum 2 <> mempty)
  3
 }}}

 I think it would be nicer if we could elide the `<has no documentation>`
 message for the `Sum` data constructor here.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15784>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler