[GHC] #13313: cabal08 broken

[GHC]

#13313: cabal08 broken
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        Reporter:  bgamari           |                Owner:  ezyang
            Type:  bug               |               Status:  new
        Priority:  high              |            Milestone:  8.2.1
       Component:  Compiler          |              Version:  8.0.1
      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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Comment (by ezyang):

 Yes, I've diagnosed the problem.

 The trouble is that the new algorithm for computing package shadowing
 doesn't remember the order packages were specified in package databases,
 so it doesn't respect the flag ordering; instead, it relies entirely on
 the (deterministic) comparison of unit identifiers. Probably the reason
 why this wobbled is because Cabal was allocating different unit
 identifiers on different platforms, causing the (deterministic) comparison
 to wobble, so that we picked one or another.

 It would be very good to fix this in time for GHC 8.2. However, fixing
 this seems a bit annoying in the current algorithm, because there isn't
 really a good way to remember the package ordering after we suck all the
 packages into an InstalledPackageIndex. I'll work on a fix this weekend.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13313#comment:5>
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