[GHC] #8407: Module re-exports at the package level

[GHC]

#8407: Module re-exports at the package level
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        Reporter:  nomeata           |            Owner:  ezyang
            Type:  feature request   |           Status:  new
        Priority:  normal            |        Milestone:
       Component:  Package system    |          Version:  7.6.3
      Resolution:                    |         Keywords:  backpack
Operating System:  Unknown/Multiple  |     Architecture:  Unknown/Multiple
 Type of failure:  None/Unknown      |       Difficulty:  Unknown
       Test Case:                    |       Blocked By:
        Blocking:                    |  Related Tickets:
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Comment (by ezyang):

 Also, so minor UI things to watch out for:

 1. Suppose a module Foo is defined by package a, and reexported by package
 b. I misspell my import and attempt to import module Fooo (sic). Clearly,
 when I give the list of corrections, I should only report Foo once. Now,
 suppose I have another module Foo defined by package c, so in our message
 we want to report that the module was found in multiple packages. In this
 case, we want to say "it was found in multiple packages: a (reexported by
 b), c" (and not just "a, c")

 2. When we validate an entry in the installed package database, should we
 check if the reexported modules truly exist in the original package?
 Depending on what representation we have in the package database, this may
 not even be well defined. In any case, dependency validation should pick
 up most shenanigans.

 3. In some functions, including packageDbModules from the GHC API, we
 asked to provide a `Module` for a re-exported module. Should the module
 returned be resolved to the original exporter, or still be the original
 name of the module?

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8407#comment:8>
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