What?

See #71735.

Addressing feedback from @justintadlock. When the user switches themes, any active templates that are associated with the previous theme should be ignored.

Why?

Currently templates are often heavily dependent on styles and patterns from the current theme.

How?

Whenever new templates are created, we already save information to the database that associates it with the current theme. Fixing the issue is just a matter of using that data:

• On the front-end, check that the active templated set for a slug is associated with the current theme, otherwise ignore it.
• In the site editor, also make sure the template is no longer marked as active. For now, I've opted to also disable the "activate" action. Users can still choose to duplicate the template, which will update the association, and maybe it available to activate. I've also added an extra field to indicate the lack of compatibility.

Please note: when you switched themes previously in WP, theme template edits would completely disappear.

Testing Instructions

• Duplicate the Home template for 2025 (for example), make some changes, and activate it.
• Switch to 2024. The Home page should now use the 2024 template, and the custom template should be inactive.

Testing Instructions for Keyboard

Screenshots or screencast