Snap refresh with no updates should be friendly about it

[Mark Shuttleworth]

When I try to refresh Krita which is already up to date I see this:

  $ snap refresh krita

  error: cannot perform the following tasks:
  - Download snap "krita" from channel "stable" (revision 1 of snap "krita" already installed)

This looks scary, because it says error. Perhaps we could say this for explicitly named snaps:

  $ snap refresh krita telegram firefox
  krita already up to date
  firefox (beta) updated
  telegram updated

So, I am explicitly giving a result for each named snap, and none of those are an error.

In the case of the general "snap refresh" we should only say something about snaps which have changes to apply:

  $ snap refresh
  firefox (beta) updated

In the case of a general snap refresh with no updates:

  $ snap refresh
  Good news, we're all up to date here

[Gustavo Niemeyer (niemeyer)]

Yeah, IIRC the branch that landed has it as

"All snaps up-to-date."

[Jamie Bennett (jamiebennett)]

Typing just snap refresh with no updates just lists the snaps installed - same as typing snap list - is this also fixed with the updated branch?

[Stuart Bishop (stub)]

I think this is fatal in my snap layer for Juju. I'm going to have to ignore the error code and continue on, crossing my fingers it is harmless and not something like a network error.

I can't 'snap find' and parse the human readable output to see if updated versions are available, since it doesn't understand channels.

I can't blindly call 'snap refresh', as that just updates all snaps and doesn't let me switch channels or confinement options.

[Stuart Bishop (stub)]

(the problem for the snap layer not being the error message, but that it returns a fatal error code making it useless for scripting)

[Jacek Nykis (jacekn)]

Unhelpful return codes were also reported as separate bugs: LP#1622782 and LP#1595064

[Stuart Bishop (stub)]

Worked around in the snap layer by sniffing the error message, which hopefully will not get localized.

[Michael Vogt (mvo)]

This has landed in snapd 2.18