Merge ~jawn-smith/ubuntu/+source/ubuntu-release-upgrader:ubuntu/jammy into ubuntu/+source/ubuntu-release-upgrader:ubuntu/jammy

See my in-line comment.

I'm afraid there's a few issues:

* I'd much rather parse the YAML with a yaml library given there's so many possible representations here (which cloud-init is free to use when it converts network-config to the netplan config). For example, match: {driver: "bcmgenet smsc95xx lan78xx"} is valid YAML. I know adding dependencies is generally frowned upon, but python3-yaml is seeded on the pi server and desktop images (presumably because cloud-init and ubuntu-advantage-tools both depend on it, among many other things) so adding it as a dep of u-r-u won't *actually* pull in anything new, would simplify this code, and deal with all possible variants of the configuration.

* If you remove the match/driver: clause, the set-name: clause becomes invalid (it requires a match: clause). In this case it's probably sufficient to just remove the set-name: clause along with the match: clause.

* Ideally the config_txt variable in the various tests should be renamed; it's not the config.txt on the boot partition that's being modified (unlike the prior tests concerned with removing u-boot), it's the netplan yaml.

Other than that: nice to see a good set of tests, covering all the netplan config scenarios (match present, not present, present but only in certain files)!

Ah I had thought about using python3-yaml but didn't want to add dependencies to the upgrader, which I figured could be problematic. I didn't check if it was seeded though.

If you are going to add python3-yaml as a dependency in jammy, then it should either (1) be SRU'd to focal and impish, or (2) there should be logic to handle a potential import exception.

This recently came up in bug 1965568, i.e. I learned this the hard way.

> If you are going to add python3-yaml as a dependency in jammy, then it should
> either (1) be SRU'd to focal and impish, or (2) there should be logic to
> handle a potential import exception.
>
> This recently came up in bug 1965568, i.e. I learned this the hard way.

Option 1 would result in there be two SRUs. One from the release being upgraded from and one for the release being upgraded to.

If it were a genuinely new dependency I would indeed worry, but I'm *fairly* sure python3-yaml's been seeded since forever (or since focal at least, which is the earliest we need to concern ourselves with as upgrades never span more than one LTS). Just checking ...

$ curl -s http://cdimage.ubuntu.com/ubuntu/releases/focal/release/ubuntu-20.04.4-preinstalled-server-arm64+raspi.manifest | grep python3-yaml
python3-yaml 5.3.1-1ubuntu0.1
$ curl -s http://cdimage.ubuntu.com/ubuntu/releases/focal/release/ubuntu-20.04.4-preinstalled-server-armhf+raspi.manifest | grep python3-yaml
python3-yaml 5.3.1-1ubuntu0.1
$ curl -s http://old-releases.ubuntu.com/releases/20.04.0/ubuntu-20.04-desktop-amd64.manifest | grep python3-yaml
python3-yaml 5.3.1-1
$ curl -s http://old-releases.ubuntu.com/releases/20.04.0/ubuntu-20.04-live-server-amd64.manifest | grep python3-yaml
python3-yaml 5.3.1-1

Yup, python3-yaml was seeded at least as far back as focal on PC server, PC desktop, and pi server images. So, technically yes, an SRU *should* be done but I wouldn't worry greatly in this particular case as python3-yaml should be universally installed.

> Yup, python3-yaml was seeded at least as far back as focal on PC server, PC
> desktop, and pi server images. So, technically yes, an SRU *should* be done
> but I wouldn't worry greatly in this particular case as python3-yaml should be
> universally installed.

Right, then option (2) is probably more appropriate in this case. William's original patch already has a helpful `failure_action` string, so this should be displayed to the user if for some reason `import yaml` raises an exception.

Some inline comments; one thing needs changing (orig_yaml being a ref to netplan_yaml) but otherwise looking much better!

Excellent, looking good now (and no, there's nothing wrong with KeyError: continue :)