I take that back. :)

Alexsander mentioned something I missed earlier.

We apparently just need to update docs,
and I have to read code more carefully. :)

...

The SNAP build _HAS_ `/etc/maas/preseeds/` as well; 
it's in the read-only side (`/snap`),
not in the read-write side (`/var/snap`).

If I look closer than I did in comment #10:

The SNAP build also runs `setup.cfg` per the `python` plugin [1],
and as such, populates `/etc/maas/preseeds` with same filenames.

	@ snap/snapcraft.yaml

	 72 parts:
	 73   maas:
	 74     plugin: python

	[1] https://snapcraft.io/docs/python-plugin

And the preseed template locations for the snap configuration
file actually include _BOTH_ of them (which I read but didn't
investigate properly):

	@ src/maasserver/djangosettings/snap.py

	 19 PRESEED_TEMPLATE_LOCATIONS = (
	 20     os.path.join(os.environ["SNAP_DATA"], "preseeds"),
	 21     os.path.join(os.environ["SNAP"], "etc", "maas", "preseeds"),
	 22 )

During test, that couldn't be picked up because of a
implementation detail / design decision, it seems:

A more generic template file in the `/var/snap` dir is _preferred over_ 
a more specific template file in the `/snap` dir.

See the order of the 2 for-loops here:

	@ src/maasserver/preseed.py

	 789 def get_preseed_template(filenames):
	 790     """Get the path and content for the first template found.
	 791
	 792     :param filenames: An iterable of relative filenames.
	 793     """
	...
	 796     for location in settings.PRESEED_TEMPLATE_LOCATIONS:
	 797         for filename in filenames:
	 798             filepath = os.path.join(location, filename)
	 799             try:
	 800                 with open(filepath, encoding="utf-8") as stream:
	 801                     content = stream.read()
	 802             except OSError:
	 803                 pass  # Ignore.
	 804             else:
	 805                 return filepath, content
	...

In my test server, there was a more generic file in /var/snap:
- /var/snap/maas/current/preseeds/curtin_userdata

which prevented the centos specific file in /snap/ to be picked:
- /snap/maas/current/etc/maas/preseeds/curtin_userdata_centos

Once I removed /var/snap/.../curtin_userdata, the changes
in /snap/.../curtin_userdata_centos were effective.


...

Well, that seems to be _the right thing to do_...

Specifically because it allows users to have their own,
_more generic_ template file that works on all releases,
and ignores the release-based templates shipped in SNAP.

...

I just think we should update the documentation about it,
right now it has 2 issues:

1) It only mentions the `/var/snap/maas/current/preseeds/`
path, which might puzzle users seeing behavior specified
in the (unknown) `/snap/maas/etc/maas/preseeds/` location.

2) The paths for DEB/SNAP are incorrectly changing due to
the UI/CLI view-change, not on DEB/SNAP change. 

https://maas.io/docs/about-customising-machines#heading--templates

We should fix it here: (note the 2 `[tab]` tags)

@ src/maas-offline-docs/src/src/about-customising-machines-5976.md

132 [tabs]
133 [tab version="v3.2 Snap,v3.2 Packages,v3.1 Snap,v3.1 Packages,v3.0 Snap,v3.0 Packages,v2.9 Snap,v2.9 Packages" view="UI"]
134 ... template files are found in the `/var/snap/maas/current/preseeds/` directory ...
135 [/tab]
136 [tab version="v3.2 Snap,v3.2 Packages,v3.1 Snap,v3.1 Packages,v3.0 Snap,v3.0 Packages,v2.9 Snap,v2.9 Packages" view="CLI"]
137 ... template files are found in the `/etc/maas/preseeds/` directory ...
138 [/tab]
139 [/tabs]