Accept license field in snapcraft.yaml

We are in the process to get some definitions for license updates via snapcraft. Trying to limit the discussion to specific points, there will be separated threads summarizing the ideas/plans for licenses per revision/per snap and handling custom licenses (@roadmr is on that).

Meanwhile we want to also confirm and check if we can move on with the license field support in snapcraft. I think the field name is already settled, so we would need snapcraft to start allowing (and validating it to avoid pushing a revision with an invalid license value?) and the reviewer-tools to consider it a valid field too.

@sergiusens, @jdstrand, do you see any blockers? Store-side we wouldn’t start extracting it until we have a decision on the per revision/snap license discussion, but it would be great to know the snapcraft bits are in the roadmap and that could be available in the short term.

The snapcraft bits are on the roadmap for early 18.10 (which starts roughly a month from now).

A couple weeks ago we agreed that we would do this in conjunction with the availability of a validation command from the snap command (which could operate standalone from snapd).

Let’s please not have more threads covering the same topics. We already have more than one on this subject, so it becomes just confusing.

How is “License in the yaml” any different from the other threads? We need to either answer that and fix the summary or fold this conversation into one of the existing topics.

Update: The summary has been changed.