[GHC] #11315: GHC doesn't restore split objects

[GHC]

#11315: GHC doesn't restore split objects
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        Reporter:  snowleopard       |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  7.10.3
      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):

 The problem is, even though `A_o_split` is supposed to be considered
 output of compilation, the recompilation checkers for `--make` and `-c`
 (the ones that determine if the source is modified) only look at the
 merged `o` file (not the split objects) to see if they've gone away.

 Distressingly, in the current scheme, it is unobvious whether or not a
 split object directory is complete or not. So this suggests that we have
 to atomically output some digest describing all of the split objects we
 expect to see. Recompilation avoidance, when running in split objects
 mode, checks to see if the digest is newer than the source file, and that
 all the files in the digest exist.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11315#comment:1>
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