zfs: mark change correctly when updating properties whose current value differs, even if they already have a non-default value (Fixes #11019)

[handisyde]

SUMMARY

Fixes #11019
Fix incorrect changed reporting in the zfs module when updating ZFS properties using extra_zfs_properties.

Previously, if a property already had a non-default value (e.g. SOURCE=local), applying a new value via extra_zfs_properties would run zfs set correctly, but the module would still return: changed: false

ISSUE TYPE

• Bugfix Pull Request

COMPONENT NAME

zfs

ADDITIONAL INFORMATION

Root cause

Previously, the module used:

            if self.get_property(prop, current_properties) != value:
                self.changed = True

But get_property() always calls zfs get again, so at that point it reads the updated value, not the original one, and != is always false for a successful change. Storing previous_values fixes this.
Check mode behaviour is unchanged: in check mode, set_property() just toggles self.changed = True and returns without running any command, and we still return diff early.

Testing Done / Evidence

Manual functional validation on a real ZFS dataset with both:

1. Local -> different local value
   • Previously: incorrectly changed: false
   • Now: changed: true ✔️
2. Local -> same value
   • changed: false ✔️

You can see the exact output below:
Dataset compression:

root@myserver:~ $ zfs get compression nvme/test
NAME       PROPERTY     VALUE           SOURCE
nvme/test  compression  zstd            local

Ansible output, changed: true:

changed: [myserver] => (item={'name': 'nvme/test', 'properties': {'compression': 'lz4'}}) => 
    ansible_facts:
        discovered_interpreter_python: /usr/bin/python3.11
    ansible_loop_var: item
    changed: true
    compression: lz4
    item:
        name: nvme/test
        properties:
            compression: lz4
    name: nvme/test
    state: present

Dataset compression correctly changed to lz4:

root@myserver:~ $ zfs get compression nvme/test
NAME       PROPERTY     VALUE           SOURCE
nvme/test  compression  lz4             local

Second Ansible run output, changed: false:

ok: [myserver] => (item={'name': 'nvme/test', 'properties': {'compression': 'lz4'}}) => 
    ansible_facts:
        discovered_interpreter_python: /usr/bin/python3.11
    ansible_loop_var: item
    changed: false
    compression: lz4
    item:
        name: nvme/test
        properties:
            compression: lz4
    name: nvme/test
    state: present

[ansibullbot]

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[russoz]

hi @handisyde thanks for your contribution!

LGTM from the Ansible perspective. Have you tested it locally? Since we do not have tests for that module in the collection, it would be nice if people who actually use the module could test it with these changes.

[felixfontein]

Thanks for your contribution!