Why does no-changed-when apply to handlers?

[AndrewKvalheim]

ansible-lint is implying that “nothing needs doing” when this handler is notified:

$ cat 'playbook.yml'
- name: Example
  hosts: example
  tasks:
    - name: Register swap file
      ansible.posix.mount: { state: present, src: /swap.img, path: none, fstype: swap, opts: sw }
      notify: Activate swap
  handlers:
    - name: Activate swap
      ansible.builtin.command: swapon --all
$ ansible-lint
WARNING  Listing 1 violation(s) that are fatal
no-changed-when: Commands should not change things if nothing needs doing.
playbook.yml:8 Task/Handler: Activate swap

Doesn’t notify already indicate that something needs doing? What is ansible-lint trying to get me to do with this?

[baldurmen]

I agree this is counter intuitive, and I feel this should be a bug

[bendem]

This was kind stated in #3237, but I think the explanation could be better. @ssbarnea, might I suggest this phrasing that actually explains the why instead of just stating that tasks are tasks?

- This rule also applies to handlers, not only to tasks because they are also
- tasks.
+ This rule also applies to handlers, handlers are idempotent tasks as well
+ and should correctly report whether their execution resulted in a change
+ or not.