Add Pushing XComs from Deferred example

[guan404ming]

Related Issue

closes #44759

Why

• lack of example for explain Trigger event from deferred task does not get scheduled immediately, leading to timeout. #44759 (comment)

How

• add one based on the Fix: Added example of _push_xcoms_if_necessary to deferring.rst #45158 with rephrasing and formatting

cc: @eladkal @tirkarthi @avyuktsoni0731

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[eladkal]

Do we have an easy way to generate a list of all our Trigger that were written before 2.10 and don't support this? so we can patch them? in ~1 week or so the min version for providers will be 2.10 so we can safely fix it.

Also maybe, an idea how to get the list... adding a test to make sure any sub class of BaseTrigger has implementation for this? That would also protect us for future adding new triggers

[guan404ming]

Sorry for the late. It took some time to deal with this. And I think this func is not supported for all triggers before 2.10.0 since there are not implementation of some thing like self.xcoms or something like the example do.
I only see the trigger test which use the functionality the example show

airflow/airflow-core/tests/unit/models/test_trigger.py

Lines 202 to 211 in c37e6eb

	@pytest.mark.parametrize(
	"event_cls, expected",
	[
	(TaskSuccessEvent, "success"),
	(TaskFailedEvent, "failed"),
	(TaskSkippedEvent, "skipped"),
	],
	)
	@patch("airflow.utils.timezone.utcnow")
	def test_submit_event_task_end(mock_utcnow, session, create_task_instance, event_cls, expected):

please let me know if there is anything I could help

[eladkal]

This is my point. Minimum version for Airflow in providers is 2.10 so we should open a tracking issue to modify all trigger we have to support it. Don't we?

[guan404ming]

After more investigation, it seems currently trigger is not accept xcoms #46677 (comment) after reworked. xcoms is passed when the event have xcoms.

Should we modify our example or try to modify trigger to accept "xcoms" when init?

[guan404ming]

I think we could leave this here until there is any re-implementation plan.