`is_callable()` should be checked in `do_shortcode_tag()`, not `add_shortcode()`

[wonderboymusic]

Actions and filters can be registered before their callbacks actually exist. The same should be true for shortcodes. This is a followup of #30947 - would be good to be able to add all shortcodes in default-filters.php

[wonderboymusic]

Another piece here - if you register a shortcode now without a valid callback, you get no notice in the logs and nothing happens to your shortcode (it isn't parsed).

32445.diff​ is all of the code that is required to make shortcode registration possible in default-filters.php. The only major diff is having to load shortcodes.php before default-filters.php in the bootstrap.

In my patch, when a shortcode is being parsed and doesn't have a valid callback, a _doing_it_wrong() is fired. _doing_it_wrong() can't be called on add_shortcode() in default-filters.php because i10n is not loaded.

[aaroncampbell]

The patch seems to work, passes all the tests, etc, but I'm a little leery of moving all our default shortcodes into default-filters.php. It all seems to work for core, but I'm convinced it won't cause issues elsewhere. Can we limit this patch to just the is_callable fix?

[nacin]

Yeah, moving add_shortcode() calls to default-filters.php will break things in weird situations, like including a few random files outside of WordPress. I'm not saying we should ever support that (and I often argue, such as in the SHORTINIT situations, that we should not), but in this case, the only functions called in default-filters.php are add_action() and add_filter() (and is_admin()). It should stay that way.

I'd agree with moving them out of here, but it should probably go to some kind of shortcodes_init() like widgets and other things. Moving them too late could break plugins that currently remove them pretty early, however. Kind of stuck here.

I do like the callback change here, though.

(Random thought, if anyone wants to have some fun, we should rewrite the API to use hooks under the hood, and ditch $shortcode_tags. And then break everyone reaching directly into $shortcode_tags.)

[aaroncampbell]

32445.2.diff​ is wonderboymusic's 32445.diff​ without the moving of the add_shortcode() calls. I think this fixes the actual problem without the extra code churn.

[wonderboymusic]

In 32867:

Check is_callable() in do_shortcode_tag(), not add_shortcode().
Add a _doing_it_wrong() in do_shortcode_tag() when is_callable() is false.

Props aaroncampbell.
See #32445.

[wonderboymusic]

Done for now