investigate: avoid updating arrow functions props if possible

Context:

Props assigned an arrow function are "ignored" (auto .alike) for re-renders 👍
... but they are not ignored for useEffect if a render actually occurs for another reason 🤔

Another way to say it: I think the intended behavior of useEffect is to "trigger when something that is read inside the effect changes" but a simple useEffect(() => { this.props.doStuff(); }) actually triggers on all renders, as doStuff gets reassigned to a new arrow function. Is this wanted?

I made a PR with a quick test to demo the issue more precisely: https://github.com/odoo/odoo/pull/278104 (the last assertion fails, I would have imagined it should not).

well, yes it is intended. the useEffect has no way of knowing that the function is actually the same. if the effect reads a reactive value (in this case this.props.doStuff), and that value is reassigned, the effect is reexecuted. Now, for the props in a template, since owl knows that the new function is actually the same closure, it does not need to update the child component.

for the props in a template, since owl knows that the new function is actually the same closure, it does not need to update the child component

If it didn't update that prop, wouldn't the problem go away too?

that's an interesting thought. not sure how easy it is to propagate the information to the useProps function and define a signal with a truthy comparison function to skip the update, but it could very well work. i'll investigate

Start with PR #278104 and its failing last assertion, then trace how arrow-function props reach useProps and how useEffect observes them. Determine whether the prop update can be skipped without changing intended reactive behavior, and add or update a focused regression test showing the expected effect execution.