Code review comment for lp://staging/~fwereade/pyjuju/fix-charm-upgrade

[6]

As we discussed over g+, this is looking good The main thing is that the callback/deferred passing should be removed in favor of having lib/statemachine.py do saving/clearing of transitions in progress against state variables. This will make generic recovery of any inflight transition and perhaps special casing in synchronize.

It should also obviate the need for _notify_upgrading, and upgrade_charm's cb_upgrading.

    @inlineCallbacks
    def _notify_upgrading(self, is_upgrading):

[7] just a comment, looking at upgrade_charm's implementation.

The distinction between upgrade.prepare, upgrade.run, and upgrade.ready looks a little superficial. The upgrade.prepare should work or raise an error. On a retry of an upgrade-charm error state we should always ..
This also has the interesting side effect of firing hooks on juju resolved if we're just now downloading the charm successfully, but that seems correct.