[GHC] #13102: orphan family instances can leak through the EPS in --make mode

[GHC]

#13102: orphan family instances can leak through the EPS in --make mode
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        Reporter:  rwbarton          |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Changes (by simonpj):

 * cc: ezyang (added)


Comment:

 Are you sure?

 It used to be the case that instances simply accumulated, so a module
 could "see" an instance (of a type class, say) that it didn't import, even
 transitively.  But I belived we fixed that some time ago.  I think it's in
 the call to `hptInstances` in `tcRnImports`.

 Ah but that's the ''home'' package, and your point is about some external
 package.

 Maybe you are right... Can you show how this can compromise type safety.
 Presumably it's through an un-detected type-family inconsistency?

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13102#comment:1>
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