Using in-development features in `snapcraft.yaml`

When in need to be able to use new features of snapd as soon as they are available, and in fact even before they are available (edge, beta, etc), but has not made it into snapcraft's validation mechanisms yet there is an option of using the passthrough attribute in snapcraft.yaml which has the following properties:

  • snapcraft will accept two new fields, named passthrough. One at the top level, and one at the application scope. In points below, these locations are referred to as the target scope.
  • When these fields exist they must necessarily contain a map.
  • Options inside the map are passed through directly into “snap.yaml”, in the target scope where the passthrough option itself lives.
  • snapcraft must forbid defining an option inside the passthrough if that option is also directly present in the target scope.
  • snapcraft must warn whenever it sees an option in the passthrough, to remind the publisher that these options are not yet supported.
  • snapcraft might learn to report options that are potentially already supported. But it must not prevent these options from being passed through, since the option may be defined in a way that is not yet understood by snapcraft and should thus pass through.

The format is as follows in way of an example:

name: foo
passthrough:
    confinement: next-generation
    planet: saturn
apps:
    foo:
        command: foo
        passthrough:
            daemon: complex

This would allow use of the fictional, not yet ready,

  • next-generation value for confinement.
  • a new planet attribute with a value of saturn.
  • a complex value for daemon for the app foo.

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