[GHC] #9855: Harbormaster uses the wrong code sometimes

[GHC]

#9855: Harbormaster uses the wrong code sometimes
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       Reporter:  goldfire           |                   Owner:  hvr
           Type:  bug                |                  Status:  new
       Priority:  normal             |               Milestone:
      Component:  Trac & Git         |                 Version:
       Keywords:                     |        Operating System:
   Architecture:  Unknown/Multiple   |  Unknown/Multiple
     Difficulty:  Unknown            |         Type of failure:
     Blocked By:                     |  None/Unknown
Related Tickets:                     |               Test Case:
                                     |                Blocking:
                                     |  Differential Revisions:
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 Harbormaster sometimes uses an inconsistent codebase for building, and
 then reports spurious build errors. A specific example is
 [https://phabricator.haskell.org/harbormaster/build/2444/ here]. The line
 where the error is reported is correct in the Differential view, but
 somehow Harbormaster is confused. Even stranger, this particular error
 could result only if ''part'' of a file were out-of-date. Something
 somewhere is trying to be awfully clever and failing.

 I know that sometimes I have deviated from any recommended Phab workflow.
 I attest that, to the best of my knowledge, I have not done so with this
 patch. It is based off my `origin/master`, and I have done no rebasing
 since posting on Phab. I have not pushed to the central GHC repo, but that
 doesn't appear to be necessary.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9855>
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