allow default card index -1

[orrpan]

No description provided.

[kingosticks]

Would you mind providing a bit of description in the commit messages as to what this solved.

[orrpan]

If you want to set card to default, it is -1. Now there is a limit to only have positive integers.

class alsaaudio.Mixer(control='Master', id=0, cardindex=-1, device='default')

docs

[adamcik]

Other option could be to leave min=0 and instead set optional=True and treat this field not being set / blank as -1 in the code (you might need to update the default config to be blank).

This IMO gives a nicer config exposed to end users than needing to know that -1 is a magical value.

Either way this is missing an update to the README documenting the new config semantics.

[orrpan]

@adamcik thats a smart solution.
But when I test
schema['card'] = config.Integer(minimum=0, optional=True)
schema['card'] = config.Integer(minimum=-1, optional=True)

cardindex becomes 0, so it seems unnecessary to add further logic than having min=-1.
Yes, I have to update README.

[adamcik]

https://github.com/mopidy/mopidy-alsamixer/blob/master/mopidy_alsamixer/ext.conf#L3 would need to blank, but I'm not 100% this would work. If it doesn't we can go ahead and merge what you have :-)