Poor error message during collect-metrics

[John A Meinel]

When an charm tries to do something that isn't allowed during collect-metrics, we get a poor error message:
unit-uo-0: 11:05:22 DEBUG unit.unit-uo-0.collect-metrics ERROR not implemented for restricted context not implemented

not implemented for restricted context not implemented

a) is redundantly redundant
b) doesn't tell you *what* is not implemented

The specific code does:
var ErrRestrictedContext = errors.NotImplementedf("not implemented for restricted context")

...

func (*RestrictedContext) GetCharmState() (map[string]string, error) {
        return nil, ErrRestrictedContext
}

And all functions just return ErrRestrictedContext.

Given that NotImplemented already adds 'not implemented' as a suffix, these should be updated to something more like:

func restrictedContext(method string) error {
  return errors.NotImplementedf("in a restricted context %s is", method)
}

func (*RestrictedContext) GetCharmState() (map[string]string, error) {
        return nil, restrictedContext("GetCharmState")
}

Which would give an error of:
"in a restricted context GetCharmState is not implemented"

I'm not super happy about it (suggestions welcome), but it is hard for me to find a nice way if we force 'not implemented' to be at the end. Either way, we need to be telling them *what* isn't implemented, because otherwise it is very hard to track down why the call is failing.

[John A Meinel (jameinel)]

Another possibility would be to clean up the error in such a way that you get the actual command that was being run. In this case I was running "state-get" so having it say

state-get not implemented in a restricted context

would be my ideal message.

Note that other than knowing we are running collect-metrics, we don't seem to have a way to know that we are running in a restricted context. So if Juju changes to no longer run collect-metrics asynchronously, we'll want a way to know that it is safe to operate as normal.

[Pen Gale (pengale)]

Agree that the error should be clearer. Marking this in the list of things to sweep up w/ the next version of 2.8.

[Canonical Juju QA Bot (juju-qa-bot)]

This bug has not been updated in 2 years, so we're marking it Low importance. If you believe this is incorrect, please update the importance.