[GHC] #10533: Typechecker behaves differently on Phab and on Mac

[GHC]

#10533: Typechecker behaves differently on Phab and on Mac
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              Reporter:  goldfire    |             Owner:
                  Type:  bug         |            Status:  new
              Priority:  normal      |         Milestone:
             Component:  Compiler    |           Version:  7.11
              Keywords:              |  Operating System:  MacOS X
          Architecture:              |   Type of failure:  None/Unknown
  Unknown/Multiple                   |        Blocked By:
             Test Case:              |   Related Tickets:
              Blocking:              |
Differential Revisions:              |
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 On my Mac, commit 61b96a86c5342fb1c850361177d60fe855d948f6 causes test
 `typecheck/should_compile/FD3` to fail. But Phab succeeded in validating
 this commit, as seen [https://phabricator.haskell.org/B4297 here]. (I
 don't believe that commit has anything to do with the failure -- it's just
 the snapshot I looked at.)

 This leads to two questions:

 1. Why does this test fail on a Mac?

 2. Why does the typechecker behave differently, at all, on two different
 platforms?

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10533>
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