Issue with the `guard` tag

[javiereguiluz]

I updated a bundle to start using the new guard tag: EasyCorp/EasyAdminBundle#6656

However, instead of the expected guard behavior, in tests you can now see a lot of messages like:

"Did you forget to run "composer require symfony/web-link"?
Unknown function "preload" in "@EasyAdmin/includes/_css_assets.html.twig"."
at UndefinedCallableHandler.php line 105

As @stof explained on Symfony Slack, this only happens when using Twig inside a Symfony application, where this class exists --> https://github.com/symfony/symfony/blob/7.3/src/Symfony/Bridge/Twig/UndefinedCallableHandler.php

@stof proposed to either change the implementation of guard in Twig to skip the undefined callback handler when checking for function existence ... or provide a way for such handlers to opt-in for such bypass.

Thanks!

[fabpot]

We cannot bypass undefined handlers as they might register functions/filters.
The problem here comes from Symfony implementation of such undefined handlers as Symfony throws an exception.
But Twig docs are very clear on this topic:

If the callable is not able to return a valid function/filter/tag, it must return false.

So, the only workaround I can see in Twig would be to catch all exceptions and ignore them.

[fabpot]

See #4511