Warn about leading "0" (octal) in snap.yaml?

I'm looking at this again in more detail now and what I don't understand is why this is a bug on ubuntu-image given that u-i doesn't parse the snap.yaml, but instead only the gadget.yaml. And the gadget.yaml doesn't define `usb-vendor` or vip/pid.

However, we already have to special case a few instances where int-like values are parsed into actual integers, from which we have to convert back into strings. What I'd like to do is parse int-like things as strings and then turn the one or two cases back into ints in post-processing. The only values that might naturally be integers are the `size` and `offset` keys, but we already have to post-process them because their values can also have suffixes.

This isn't a bug in ubuntu-image. The crash is coming from `snap prepare-image` and u-i just forwards that along because there's nothing more it can do. I opened a bugtask for snapd; here's how to reproduce it.

1. wget the model and the gadget snap from w-ondra's attachements
2. ubuntu-image --channel edge -o ../images/ondra.img -d ../models/pi3-ondra.model --extra-snap ../ondra/pi3-ondra_16.04-0.5_armhf.snap

Here's the full traceback so you can see it's coming from snap.

DEBUG:ubuntu-image:-> [ 0] make_temporary_directories
DEBUG:ubuntu-image:-> [ 1] prepare_image
error: attribute "usb-vendor" of slot "zwave-aeon-g5": invalid attribute scalar: 658
ERROR:ubuntu-image:COMMAND FAILED: snap prepare-image --channel=edge --extra-snaps=../ondra/pi3-ondra_16.04-0.5_armhf.snap ../models/pi3-ondra.model /tmp/tmpsbngmcs_/unpack
ERROR:ubuntu-image:Full debug traceback follows
Traceback (most recent call last):
  File "/home/barry/projects/ubuntu/allsnappy/ubuntu-image/ubuntu_image/builder.py", line 128, in prepare_image
    self.args.channel, self.args.extra_snaps)
  File "/home/barry/projects/ubuntu/allsnappy/ubuntu-image/ubuntu_image/helpers.py", line 116, in snap
    run(cmd, stdout=None, stderr=None, env=os.environ)
  File "/home/barry/projects/ubuntu/allsnappy/ubuntu-image/ubuntu_image/helpers.py", line 97, in run
    proc.check_returncode()
  File "/usr/lib/python3.5/subprocess.py", line 659, in check_returncode
    self.stderr)
subprocess.CalledProcessError: Command '['snap', 'prepare-image', '--channel=edge', '--extra-snaps=../ondra/pi3-ondra_16.04-0.5_armhf.snap', '../models/pi3-ondra.model', '/tmp/tmpsbngmcs_/unpack']' returned non-zero exit status 1

In can reproduce this. As a workaround you can remove the leading "0". It looks like for some reason our yaml parser is parsing 0658 as an float64 (which we don't support, only ints are allowed).

Ok, so - in yaml the leading "0" means octal. And "0658" is of course not a valid octal number. Which looks like we need to warn about those leading "0" to avoid confusion.

Hey Michael.

I've assigned this bug to you since you have indicated that it is in progress. Since the bug was last updated quote a while ago, could you please look at this and decide if it is still an issue, if it is really in progress and if you are willing to work on it?