[GHC] #10077: Providing type checker plugin on command line results in false cyclic import error

[GHC]

#10077: Providing type checker plugin on command line results in false cyclic
import error
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        Reporter:  jbracker          |                   Owner:
            Type:  bug               |                  Status:  new
        Priority:  normal            |               Milestone:
       Component:  Compiler (Type    |                 Version:  7.11
  checker)                           |                Keywords:
      Resolution:                    |  typechecker plugin cycle imports
Operating System:  Linux             |            Architecture:  x86_64
 Type of failure:  Incorrect         |  (amd64)
  warning at compile-time            |               Test Case:
      Blocked By:                    |                Blocking:
 Related Tickets:                    |  Differential Revisions:
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Comment (by jbracker):

 Replying to [comment:5 adamgundry]:
 > To try to clarify: it's not exactly true that the plugin needs to be
 **imported** into a module that uses it, although I believe the
 implementation works more-or-less like that, with some cleverness to avoid
 e.g. typeclass instances being brought in. The point is that if module `M`
 uses a plugin in module `P`, then we have to dynamically load `P` in order
 to typecheck `M`. Hence `P` cannot depend (directly or indirectly) on `M`!
 >
 > When `-fplugin=P` is used on the command-line, GHC tries to load `P` for
 every module being compiled, which might include `P` itself. This isn't
 exactly a cyclic import, but it's pretty close.

 Thank you for the clarification. I understand now.

 > > Maybe a link to this ticket, in case someone wants to know more about
 the issue?
 >
 > Yes. Done.

 Thanks!

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10077#comment:6>
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