[tahoe-lafs-trac-stream] [Tahoe-LAFS] #3399: Evaluate adding mypy checks to code checks

[Tahoe-LAFS]

#3399: Evaluate adding mypy checks to code checks
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     Reporter:  jaraco       |      Owner:
         Type:  enhancement  |     Status:  new
     Priority:  normal       |  Milestone:  Support Python 3
    Component:  unknown      |    Version:  n/a
   Resolution:               |   Keywords:
Launchpad Bug:               |
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Comment (by jaraco):

 Investigating in that issue, I learned quite a bit about how mypy works.
 It seems that because Twisted isn't typed, it requires stubs to
 effectively communicate its interfaces (and not trip up on the decorator
 syntax). I ended up trying two approaches:

 - [[https://github.com/jaraco/tahoe-
 lafs/tree/3399.mypy.workaround|3399.mypy.workaround]] applies a clumsy but
 effective workaround that addresses this one error.
 - [[https://github.com/jaraco/tahoe-lafs/tree/3399.mypy.twisted-
 stubs|3399.mypy.twisted-stubs]] creates twisted stubs, first from twisted
 trunk, then from the latest stable. However, this approach creates many
 more errors than it satisfies, probably because adding the stubs removes
 the mask of errors from `ignore_missing_imports`.

 Based on that, I'm going to try to proceed with addressing the type errors
 without twisted stubs for now and see how far I can get without relying on
 twisted stubs, a [[https://twistedmatrix.com/trac/ticket/9717|non-trivial
 effort]].

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Ticket URL: <https://tahoe-lafs.org/trac/tahoe-lafs/ticket/3399#comment:16>
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