Unset a subtree crashes

Yes. Looks like you discovered a bug here.
It works if you unset an "interface subtree", e.g.:
$ sudo netplan set network.bridges.br54=null

But apparently not if you delete a whole set of devices, that might be spread across a set of YAML files (like network.bridges=null, network=null).

I can reproduce the issue with a simple unit-test in `test_clie_get_set.py` and we should fix it.

    def test_set_delete_subtree(self):
        with open(self.path, 'w') as f:
            f.write('''network:\n version: 2\n renderer: NetworkManager
  ethernets:
    eth0: {addresses: [1.2.3.4/24]}''')
        ret = self._set(['network.ethernets=null'])
        print(ret, flush=True) # debugging
        self.assertTrue(os.path.isfile(self.path))
        with open(self.path, 'r') as f:
            out = f.read()
            print(out, flush=True) # debugging
            self.assertIn('network:\n', out)
            self.assertIn(' version: 2\n', out)
            self.assertIn(' renderer: NetworkManager\n', out)
            self.assertNotIn('ethernets:', out)

https://github.com/canonical/netplan/pull/236

This bug was fixed in the package netplan.io - 0.103-0ubuntu7

---------------
netplan.io (0.103-0ubuntu7) impish; urgency=medium

  * Add d/p/0006-netplan-set-make-it-possible-to-unset-a-whole-devtyp.patch:
    Fix unset of a devtype subtree, e.g. "netplan set network.ethernets=null".
    (LP: #1942930)

 -- Lukas Märdian <email address hidden> Tue, 05 Oct 2021 09:41:31 +0200

Hello Michael, or anyone else affected,

Accepted netplan.io into hirsute-proposed. The package will build now and be available at https://launchpad.net/ubuntu/+source/netplan.io/0.103-0ubuntu5~21.04.2 in a few hours, and then in the -proposed repository.

Please help us by testing this new package. See https://wiki.ubuntu.com/Testing/EnableProposed for documentation on how to enable and use -proposed. Your feedback will aid us getting this update out to other Ubuntu users.

If this package fixes the bug for you, please add a comment to this bug, mentioning the version of the package you tested, what testing has been performed on the package and change the tag from verification-needed-hirsute to verification-done-hirsute. If it does not fix the bug for you, please add a comment stating that, and change the tag to verification-failed-hirsute. In either case, without details of your testing we will not be able to proceed.

Further information regarding the verification process can be found at https://wiki.ubuntu.com/QATeam/PerformingSRUVerification . Thank you in advance for helping!

N.B. The updated package will be released to -updates after the bug(s) fixed by this package have been verified and the package has been in -proposed for a minimum of 7 days.

Hello Michael, or anyone else affected,

Accepted netplan.io into focal-proposed. The package will build now and be available at https://launchpad.net/ubuntu/+source/netplan.io/0.103-0ubuntu5~20.04.2 in a few hours, and then in the -proposed repository.

Please help us by testing this new package. See https://wiki.ubuntu.com/Testing/EnableProposed for documentation on how to enable and use -proposed. Your feedback will aid us getting this update out to other Ubuntu users.

If this package fixes the bug for you, please add a comment to this bug, mentioning the version of the package you tested, what testing has been performed on the package and change the tag from verification-needed-focal to verification-done-focal. If it does not fix the bug for you, please add a comment stating that, and change the tag to verification-failed-focal. In either case, without details of your testing we will not be able to proceed.

Further information regarding the verification process can be found at https://wiki.ubuntu.com/QATeam/PerformingSRUVerification . Thank you in advance for helping!

N.B. The updated package will be released to -updates after the bug(s) fixed by this package have been verified and the package has been in -proposed for a minimum of 7 days.

All autopkgtests for the newly accepted netplan.io (0.103-0ubuntu5~21.04.2) for hirsute have finished running.
The following regressions have been reported in tests triggered by the package:

netplan.io/0.103-0ubuntu5~21.04.2 (arm64)

Please visit the excuses page listed below and investigate the failures, proceeding afterwards as per the StableReleaseUpdates policy regarding autopkgtest regressions [1].

https://people.canonical.com/~ubuntu-archive/proposed-migration/hirsute/update_excuses.html#netplan.io

[1] https://wiki.ubuntu.com/StableReleaseUpdates#Autopkgtest_Regressions

Thank you!

Hm, maybe I'm holding it wrong (again) but I'm not sure this is fully fixed:
$ apt list netplan.io
netplan.io/now 0.103-0ubuntu5~21.04.2 amd64 [installed,local]
$ $ zcat /usr/share/doc/netplan.io/changelog.Debian.gz |head -n 6
netplan.io (0.103-0ubuntu5~21.04.2) hirsute; urgency=medium

  * Backport patches from impish:
    + Add d/p/0006-netplan-set-make-it-possible-to-unset-a-whole-devtyp.patch:
      Fix unset of a devtype subtree, e.g. "netplan set network.ethernets=null"
      (LP: #1942930)
$ netplan get
network:
  renderer: NetworkManager
  version: 2
 netplan set network=null
Traceback (most recent call last):
  File "/usr/sbin/netplan", line 23, in <module>
    netplan.main()
  File "/usr/share/netplan/netplan/cli/core.py", line 50, in main
    self.run_command()
  File "/usr/share/netplan/netplan/cli/utils.py", line 310, in run_command
    self.func()
  File "/usr/share/netplan/netplan/cli/commands/set.py", line 53, in run
    self.run_command()
  File "/usr/share/netplan/netplan/cli/utils.py", line 310, in run_command
    self.func()
  File "/usr/share/netplan/netplan/cli/commands/set.py", line 103, in command_set
    hints = self.split_tree_by_hint(set_tree)
  File "/usr/share/netplan/netplan/cli/commands/set.py", line 59, in split_tree_by_hint
    for devtype in network:
TypeError: 'NoneType' object is not iterable

But maybe that is a different bug that needs to be reported differently. Anyway, I can probably work around this one.

I don't know if you're holding it wrong per se, but at the very least
you've moved the goalpost a little bit. My patchset addresses the case

netplan set network.ethernets=null

but NOT the case

netplan set network=null

I suppose we could special-case the latter one by simply nuking all
config files... ¯\_(ツ)_/¯

Indeed, a `netplan set network=null` would basically be the same as `rm /etc/netplan/*.yaml`.

I Tested netplan.io 0.103-0ubuntu5~21.04.2 inside a fresh Hirsute LXD container:
$ lxc launch ubuntu-daily:hirsute hh
$ lxc exec hh bash

=> Enabled hirsute-proposed & installed/upgraded netplan.io

root@hh:~# dpkg -l | grep netplan
ii libnetplan0:amd64 0.103-0ubuntu5~21.04.2
ii netplan.io 0.103-0ubuntu5~21.04.2
root@hh:~# cat /etc/netplan/00-ethernets.yaml
network:
  version: 2
  ethernets:
    all-en:
      dhcp4: true
      match:
        name: en*
    all-eth:
      dhcp4: true
      match:
        name: eth*
root@hh:~# netplan get
network:
  ethernets:
    all-en:
      dhcp4: true
      match:
        name: en*
    all-eth:
      dhcp4: true
      match:
        name: eth*
  version: 2
root@hh:~# netplan set network.ethernets=null
root@hh:~# netplan get
{}

In accordance with https://wiki.ubuntu.com/NetplanUpdates I'm also attaching the full autopkgtest logs for those builds:
https://git.launchpad.net/~slyon/+git/files/tree/LP1943120/hirsute_amd64.log
https://git.launchpad.net/~slyon/+git/files/tree/LP1943120/hirsute_arm64.log
https://git.launchpad.net/~slyon/+git/files/tree/LP1943120/hirsute_armhf.log
https://git.launchpad.net/~slyon/+git/files/tree/LP1943120/hirsute_ppc64el.log
https://git.launchpad.net/~slyon/+git/files/tree/LP1943120/hirsute_s390x.log

The mentioned autopkgtest regression is gone after a retry.

I Tested netplan.io 0.103-0ubuntu5~20.04.2 inside a fresh Focal LXD container:
$ lxc launch ubuntu-daily:focal ff
$ lxc exec ff bash

=> Enabled focal-proposed & installed/upgraded netplan.io

root@ff:~# dpkg -l | grep netplan
ii libnetplan0:amd64 0.103-0ubuntu5~20.04.2
ii netplan.io 0.103-0ubuntu5~20.04.2
root@ff:~# rm /etc/netplan/*
root@ff:~# cat /etc/netplan/00-ethernets.yaml
network:
  version: 2
  ethernets:
    all-en:
      dhcp4: true
      match:
        name: en*
    all-eth:
      dhcp4: true
      match:
        name: eth*
root@ff:~# netplan get
network:
  ethernets:
    all-en:
      dhcp4: true
      match:
        name: en*
    all-eth:
      dhcp4: true
      match:
        name: eth*
  version: 2
root@ff:~# netplan set network.ethernets=null
root@ff:~# netplan get
{}

In accordance with https://wiki.ubuntu.com/NetplanUpdates I'm also attaching the full autopkgtest logs for those builds:
https://git.launchpad.net/~slyon/+git/files/tree/LP1943120/focal_amd64.log
https://git.launchpad.net/~slyon/+git/files/tree/LP1943120/focal_arm64.log
https://git.launchpad.net/~slyon/+git/files/tree/LP1943120/focal_armhf.log
https://git.launchpad.net/~slyon/+git/files/tree/LP1943120/focal_ppc64el.log
https://git.launchpad.net/~slyon/+git/files/tree/LP1943120/focal_s390x.log

This bug was fixed in the package netplan.io - 0.103-0ubuntu5~21.04.2

---------------
netplan.io (0.103-0ubuntu5~21.04.2) hirsute; urgency=medium

  * Backport patches from impish:
    + Add d/p/0006-netplan-set-make-it-possible-to-unset-a-whole-devtyp.patch:
      Fix unset of a devtype subtree, e.g. "netplan set network.ethernets=null"
      (LP: #1942930)
    + Add d/p/0005-Implement-YAML-state-tracking-and-use-it-in-the-DBus.patch:
      Allow to pass a state to netplan apply/try so it can cleanup unused
      virtual network interfaces after itself. Make use of this functionality
      inside the DBus Config.Try()/Apply() API and the 'netplan try' CLI.
      (LP: #1943120)

 -- Simon Chopin <email address hidden> Wed, 06 Oct 2021 12:57:35 +0200

The verification of the Stable Release Update for netplan.io has completed successfully and the package is now being released to -updates. Subsequently, the Ubuntu Stable Release Updates Team is being unsubscribed and will not receive messages about this bug report. In the event that you encounter a regression using the package from -updates please report a new bug using ubuntu-bug and tag the bug report regression-update so we can easily find any regressions.

This bug was fixed in the package netplan.io - 0.103-0ubuntu5~20.04.2

---------------
netplan.io (0.103-0ubuntu5~20.04.2) focal; urgency=medium

  * Backport patches from impish:
    + Add d/p/0006-netplan-set-make-it-possible-to-unset-a-whole-devtyp.patch:
      Fix unset of a devtype subtree, e.g. "netplan set network.ethernets=null"
      (LP: #1942930)
    + Add d/p/0005-Implement-YAML-state-tracking-and-use-it-in-the-DBus.patch:
      Allow to pass a state to netplan apply/try so it can cleanup unused
      virtual network interfaces after itself. Make use of this functionality
      inside the DBus Config.Try()/Apply() API and the 'netplan try' CLI.
      (LP: #1943120)

 -- Simon Chopin <email address hidden> Wed, 06 Oct 2021 12:57:35 +0200