snapm: fix Manager.split_snapshot_sets() with empty sources

[bmr-cymru]

The snapm.manager.Manger.split_snapshot_sets() method checks whether the original snapshot set would be empty after the operation and raises an error if this is the case. There is no corresponding check to ensure that the destination snapshot set is not empty (i.e. the sources passed to the split_snapshot_set() method were empty).

The snapm.command wrappers already require the sources argument:

  root@localhost:~/src/git/snapm# snapm snapset split upgrade noupgrade
  usage: snapm snapset split [-h] NAME NEW_NAME SOURCE [SOURCE ...]
  snapm snapset split: error: the following arguments are required: SOURCE

But the API does not enforce this, leading to a snapshot set with no sources and NrSnapshots == 0:

  >>> p = m.split_snapshot_set("upgrade", "noupgrade", [])
  DEBUG - Blocking termination signals {<Signals.SIGINT: 2>, <Signals.SIGTERM: 15>}
  INFO - Attempting to split snapshot set 'upgrade'
  DEBUG - Splitting snapshot  from snapshot set 'upgrade'
  INFO - Attempting rename for snapshot set 'upgrade' to 'noupgrade'
  DEBUG - Unblocking termination signals {<Signals.SIGINT: 2>, <Signals.SIGTERM: 15>}
  >>> p
  <snapm._snapm.SnapshotSet object at 0x7eff5a90d220>
  >>> print(p)
  SnapsetName:      noupgrade
  Sources:
  NrSnapshots:      0
  Time:             2025-04-01 15:02:37
  UUID:             fab385b4-5912-54f6-8458-9b487eaf7b50
  Status:           Active
  Autoactivate:     yes
  Bootable:         no

In practice this makes the call a no-op but it's pointless and confusing to allow this combination of arguments: raise a SnapmArgumentError if the source_specs list is empty or None.

Fixes: a32e85f
Related: #98, #174
Resolves: #179

[packit-as-a-service]

Congratulations! One of the builds has completed. 🍾

You can install the built RPMs by following these steps:

• sudo yum install -y dnf-plugins-core on RHEL 8
• sudo dnf install -y dnf-plugins-core on Fedora
• dnf copr enable packit/snapshotmanager-snapm-180
• And now you can install the packages.

Please note that the RPMs should be used only in a testing environment.