fix: handle ill-formed profiles created by older rockcraft

[cmatsuoka]

Older versions of rockcraft may have created a rockcraft lxd project
containing a broken default profile. If this is the case, tell
the user to delete the project and start over.

• Have you followed the guidelines for contributing?
• Have you signed the CLA?
• Have you successfully run tox?

---

[cmatsuoka]

Unfortunately deleting the broken projects ourselves involves deleting everything the project is using first, and this is too risky to implement without better investigation and careful testing.

[sergiusens]

this you be a good scenario to have a test for, aside from that, I generally approve of the appoach

[tigarmo]

I agree that this new check should have a test

[mr-cal]

Is this a duplicate of #436?

[tigarmo]

I believe there are failing unit tests

[cmatsuoka]

Is this a duplicate of #436?

It's a similar check, but performed on the specific project's default profile instead of the default project default profile.

[Copilot]

Pull request overview

This PR adds validation to detect and handle ill-formed LXD profiles that may have been created by older versions of rockcraft. When an empty devices section is detected in the default profile, the user is instructed to delete the project so it can be recreated properly.

Key Changes

• Added validation logic to check for empty devices in the default profile before launching environments
• Imported LXD_INSTALL_HELP constant to provide consistent help text in error messages
• Raises a descriptive LXDError when an ill-formed profile is detected

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[Copilot]

The condition if not devices: will be true for both None (key not present) and an empty dict {}. If the devices key exists but is an empty dict, this might be a legitimate state rather than an error. Consider checking specifically for None with if devices is None: or clarifying whether an empty dict should also trigger the error.

Suggested change

	if not devices:
	if devices == {}:

[Copilot]

If profile_show raises an exception (e.g., if the default profile doesn't exist), the error message to the user may be confusing. Consider adding error handling to catch profile lookup failures and provide a clearer message about the missing or inaccessible profile.

Suggested change

	devices = self.lxc.profile_show(
	project=self.lxd_project, profile="default", remote=self.lxd_remote
	).get("devices")
	try:
	devices = self.lxc.profile_show(
	project=self.lxd_project, profile="default", remote=self.lxd_remote
	).get("devices")
	except Exception as exc:
	# Could not access the default profile; provide a clear error message.
	raise LXDError(
	brief="LXD project is missing or has an inaccessible default profile.",
	details=(
	f"Could not access the default profile in the LXD project '{self.lxd_project}'.\n"
	f"Error: {exc}"
	),
	resolution=(
	f"Delete the '{self.lxd_project}' LXD project, it will be "
	"recreated in the next execution.\n" + LXD_INSTALL_HELP
	),
	)