inherit tags for canned_actions

[rossmeier]

Thanks to canned action, it is very easy to create dependency errors
with code like this:

svc_systemd = {
    'test.service': {
        'tags': {'a'},
        'needed_by': {'!tag:a'},
    },
}

Therefore canned actions should inherit the tags of their parent
actions to avoid confisions by using the !tag:foobar selector.

[trehn]

@CroneKorkN do you agree?

[trehn]

related to #568 and #560

[CroneKorkN]

I actually have a usecase, where i need to tag each action independently: there are tags representing stages of app deployent, like install, start, setup, stop or restart. When we need to do something after an app has started, but before it was stopped, we do something like

action['setup_app'] = {
  'action': 'some setup stuff',
  'needs': ['tag:app-start.target'],
  'needed_by': ['tag:app-stop.target'],
}

Maybe this could be resolved via an explicit svc_systemd:test:start canned action, wich is triggered by default. Then tags on the base item could be inherited by canned actions und still each action could be tagged individually, if needed.

[rossmeier]

I don't see a conflict between this PR and @CroneKorkN 's suggestion. Inheriting tags could still be the default behaviour that could be made overwriteable in a future commit/PR

[trehn]

The problem is that this isn't backwards-compatible. Right now we actually have bundles that depend on a tag which is assigned to a service and world break if that dependency were to suddenly include the restart action as well.

Nevertheless, I still agree that the behavior implemented in this PR is probably the right way to go, so I'm tagging it for 5.0.

[rossmeier]

Thanks for the reply. I guess I will use a patched bundlewrap version until then.