[GHC] #13321: Importing a bundled pattern "infects" all other imports of that pattern

22 Feb 2017

      #13321: Importing a bundled pattern "infects" all other imports of that pattern
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           Reporter:  ezyang         |             Owner:  (none)
               Type:  bug            |            Status:  new
           Priority:  low            |         Milestone:
          Component:  Compiler       |           Version:  8.0.1
  (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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 Consider:

 {{{
 {-# LANGUAGE PatternSynonyms #-}
 unit p where
     module A0 where
         data G = G Int
     module A1 where
         import A0
         pattern X x = G x
     module A(G(X)) where
         import A0
         import A1
     module B(G) where
         import A
     module C(pattern X) where
         import A
     module D(N.G, pattern N.X) where
         import B
         import C
         import qualified A0 as N
         import qualified A1 as N
 }}}

 When we look at the interface for D, we see that N is bundled with D. This
 is a little surprising because I explicitly exported the G and X from A0
 and A1, where no bundling took place.

 I suppose the current semantics might also be alright, but we should
 explicitly say so. The spec in the wiki is silent in this respect:
 https://ghc.haskell.org/trac/ghc/wiki/PatternSynonyms/AssociatingSynonyms

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Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13321
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