[GHC] #14396: Hs-boot woes during family instance consistency checks

[GHC]

#14396: Hs-boot woes during family instance consistency checks
-------------------------------------+-------------------------------------
        Reporter:  simonpj           |                Owner:  (none)
            Type:  bug               |               Status:  patch
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.2.1
      Resolution:                    |             Keywords:  hs-boot
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D4154
       Wiki Page:                    |
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Comment (by simonpj):

 That sounds good.

 I suppose the worry is that, in Core, we might end up with something like
 {{{
 case x of
   A -> e1
   B -> e2
 }}}
 but find that `x :: T` and `T` is abstract (because it somehow came from
 the hs-boot file), whereas `T` is defined in this module with constructors
 `A` and `B`.

 I can't see how this (or something like it) could happen; but I'm not sure
 how to convince ourselves that this can't.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14396#comment:8>
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