[GHC] #13152: Provide a mechanism to notify build system when .hi file is ready

[GHC]

#13152: Provide a mechanism to notify build system when .hi file is ready
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        Reporter:  rwbarton          |                Owner:
            Type:  feature request   |               Status:  new
        Priority:  normal            |            Milestone:  8.2.1
       Component:  Driver            |              Version:  8.1
      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 rwbarton):

 I'm not sure. What if the interface file already existed, and either (1)
 we checked that we don't need to recompile (in which we currently don't
 touch the interface file at all), or (2) we do need to recompile and write
 out a new interface file?

 Programming with inotify can be fiddly (for example, the man page says
 that it is possible for events to be lost), and I don't know whether we
 could reliably distinguish a new/unchanged-but-confirmed-valid interface
 file from a stale one.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13152#comment:2>
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