[GHC] #9006: GHC accepts import of private data constructor if it has the same name as the type

[GHC]

#9006: GHC accepts import of private data constructor if it has the same name as
the type
--------------------------+------------------------------------------------
       Reporter:          |             Owner:
  Lemming                 |            Status:  new
           Type:  bug     |         Milestone:
       Priority:  normal  |           Version:  7.8.2
      Component:          |  Operating System:  Unknown/Multiple
  Compiler                |   Type of failure:  GHC accepts invalid program
       Keywords:          |         Test Case:
   Architecture:          |          Blocking:
  Unknown/Multiple        |
     Difficulty:          |
  Unknown                 |
     Blocked By:          |
Related Tickets:          |
--------------------------+------------------------------------------------
 {{{
 $ cat A.hs B.hs
 module A (T) where

 data T = T

 module B where

 import A (T(T))
 }}}
 `ghci-7.8.2` accepts module B, whereas `ghci-7.6.3` and `ghci-7.4.2` say:
 {{{
 B.hs:3:11: Module `A' does not export `T(T)'
 }}}
 For this bug to happen it is important, that the data constructor has the
 same name as the type.
 I.e. if you rename the data constructor to, say, `Cons`, then `ghci-7.8.2`
 will emit the same error as earlier versions.
 The bug is not dramatic, since if you try to actually use the imported
 data constructor then ghc will say
 {{{
 B.hs:20:5:
     Not in scope: data constructor ‘T’
 }}}
 However this error message is very confusing, because it suggests that `T`
 is not in scope although you imported it correctly.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9006>
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