[GHC] #12567: `ghc --make` recompiles unchanged files when using `-fplugin` OPTIONS

[GHC]

#12567: `ghc --make` recompiles unchanged files when using `-fplugin` OPTIONS
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        Reporter:  heisenbug         |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  7.10.3
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Compile-time      |  Unknown/Multiple
  performance bug                    |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by ezyang):

 So, there's actually a deeper set of bugs here. See also #7414 and #7277.
 It would be nice if we could get our hands on an implementation hash; then
 we can just record it in the interface file directly as a plugin hash and
 fix things more properly.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12567#comment:6>
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