Snappy: Add support for snapcraft builds

[kinnison]

This commit enables building snaps for the various platforms supported by snapcraft.io

Currently the snap is under my personal page, and despite building it here, we'll keep that until after all-hands where I'll have a chat with t-release people about what we might do for an official snap. So far I've had no joy looking at official methods of distributing rustup in other channels such as flatpak.

[tesuji]

Honestly, I may know less about snapcraft than you. I would prefer to
make ci/snapcraft.sh a bash script with .bash extension instead to
make use of bash features - array, also because this script is not intended
to used by other parties (just in our CI).

[tesuji]

We may want to use bash feature - array instead.

[kinnison]

I'm not a shell person. I'm happy if you can tell me what to do there, otherwise this can stay until you want to fix it later

[tesuji]

Basic uses of bash array if you want to try: https://devhints.io/bash#arrays

[kinnison]

@lzutao Thank you for the comprehensive review. I believe I've tackled everything you hilighted (except the one thing I don't feel confident in) -- could you recheck please?

[tesuji]

Basic uses of bash array if you want to try: https://devhints.io/bash#arrays

[tesuji]

r=me with or with out using bash array, unless others disagree.

[kinnison]

Thank you @lzutao

We won't be merging this until I've spoken to the release team about snaps, but it's good to know you're now satisfied with my awful shell code :-D

[rbtcollins]

Sure, why not.

[bors]

☔ The latest upstream changes (presumably #1916) made this pull request unmergeable. Please resolve the merge conflicts.

[kinnison]

Now that we're a bit further on in our releases, and Windows builds are no longer always failing; I'll give this some more thought.

[kinnison]

I've started a discussion with Snap people about github actions for this kind of thing. Depending on how that goes, I'll either rework this PR, or close it and open a fresh one for continued discussion around rustup and snapcraft.

[kinnison]

I now need to wait for an appropriate publish action to be written and we can proceed further.

[jhenstridge]

I've left a few drive-by comments after the discussion on the Snapcraft forum. I've been working on an action to publish snaps here:

https://github.com/jhenstridge/snapcraft-publish-action

I haven't quite locked down the API yet, but it is functional. As the action depends on a secret (the Snap Store credentials), I'm not sure how easy it will be to test within a pull request.

[kinnison]

@jhenstridge Thank you for your input and review -- I'll look at the publish action you've provided and I can probably test it by adding the secret to my own repo fork and trying it there to ensure it behaves OK. I'll try and do that soon.

[kinnison]

@jhenstridge I think that ought to do the trick, obviously I'm tied to a particular commit of your repo for now. I tested it over at my own fork and it seemed to do the right thing, so now I need to wait for you to finalise a v1 of the publish action I guess, and then decide on the final comments you made on the snapcraft yaml file.

[kinnison]

I believe everything is right now, and I've added the token to the repo's secrets ready for post-merge use. If noone objects, I'll merge this soon and we can see how that goes.

[rbtcollins]

One question, one requested change

[rbtcollins]

Is the shell script shellchecked automatically?

[kinnison]

@rbtcollins Yes, shellcheck is run over all our shell scripts as part of the CI.

[kinnison]

@rbtcollins I believe your question and change were resolved. I've updated to use the now official snapcore actions. I think we're likely good to merge assuming the CI remains green. Opinions?

[kinnison]

I have decided to go ahead and merge this because we need to work through any problems long before we make a release, and we can only do that once it's trying to push to snapstore etc.