Templates: Use theme mods rather than taxonomy

[Bernhard Reiter]

As @manfcarlo explains in ​https://github.com/WordPress/gutenberg/pull/31971 and ​https://github.com/WordPress/gutenberg/issues/31954, we should consider using theme mods (rather than a wp_theme taxonomy to associate wp_template (and wp_template_part) CPTs with their corresponding theme.

Based on @carlomanf's ​https://github.com/WordPress/gutenberg/pull/31971.

More details to follow.

Trac ticket: https://core.trac.wordpress.org/ticket/53354

A little update for everyone following this: @youknowriad and I decided not to include this in the Beta 1, since I barely just got it in shape (and tests to pass). We'll allow some more time for testing and discussion of the potential impact.

It seems like the other discussion over at ​https://github.com/WordPress/gutenberg/pull/31971 got a bit heated. That's understandable, since it's a significant change to the inner workings of the templating system that (for a number of reasons) comes fairly late into the WP 5.8 release cycle.

I find both sides of the argument understandable: On one hand, it's desirable to avoid the requirement for a later migration (if we keep using the taxonomy, and in a later WP version decide to switch to theme mods). OTOH, this hasn't gone through the same amount of testing by Full-Site Editing folks as the taxonomy-based system, and we might lose "free" block template exports.

We might disagree on the impact and importance of these aspects, but let's keep in mind that ultimately, we all mean well for the project; we might have different opinions, and assign different weight to various aspects, but I'm sure we'll be able to arrive at a good conclusion if we respect each others' opinions ❤️

We decided to hold off on this change for the 5.8 release. See ​https://github.com/WordPress/gutenberg/pull/31971#issuecomment-859556344 for more details.

[poena]

I wonder if this ticket should be closed as wontfix, or if it is still considered for a later version of WP?
I think this would need to be part of a bigger plan regarding using block theme templates and template parts in multiple themes.

If it must not be closed, @bernhard-reiter can you please update the ticket with a summary of the problem as well as the proposed solution? It is too overwhelming to try to catch up with the massive linked Gutenberg conversation, especially years later.

[manfcarlo]

I forgot there was a trac ticket for this. In my opinion, if this was going to be done, it needed to be in 5.8 or 5.9, which obviously didn't happen. At today's stage, changing the data model in production would be too risky unless there were detailed designs about how it is going to be used, which also hasn't happened. There is also no guarantee that, once the designs are done, the data model proposed here would be the most suitable one. Nor was there any guarantee about the taxonomy-based one either, and most people seemed to agree that it would need to be replaced at some point, but the longer it waits, the more carefully planned and tested the alternative needs to be, and I don't see this particular trac ticket being involved in the process.