[GHC] #11164: No way to import a data instance

[GHC]

#11164: No way to import a data instance
-------------------------------------+-------------------------------------
        Reporter:  Feuerbach         |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  7.10.2
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  phab:D1573
       Wiki Page:                    |
-------------------------------------+-------------------------------------
Changes (by simonpj):

 * owner:  kanetw =>
 * status:  closed => new
 * resolution:  fixed =>


Comment:

 Wait a sec.
 [https://downloads.haskell.org/~ghc/latest/docs/html/users_guide/type-
 families.html#data-family-import-export Section 7.7.4 of the user manual]
 describes how the rules for exports are modified for families; so it
 definitely needs a new bullet!

 And the adjustment in `exports_from_avail` is delicate. It actually only
 fires on data families, because only with data families can we have a
 ''locally-defined'' subordinate thing (data constructor, class op) whose
 parent type constructor is ''imported''.  Worth spelling this out.  All
 this only applies for modules with no export list.

 The comment says "Generally, whenever we export a part of a declaration,
 export the declaration, too."  That seems a bit misleading, doesn't it?
 It really only applies to data families.

 So I'm ok with the code but I do think the documentation needs a little
 work (comments, user manual).

 Many thanks!

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11164#comment:10>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler