`theme.json` properties can't be overridden in PHP

[chrisvanpatten]

Description

theme.json properties cannot be (easily) overridden on the server-side due to the current implementation of filtering the block editor settings at a priority set to PHP_INT_MAX.

Being able to filter theme.json from PHP is a valuable way to ease the on-ramp to theme.json adoption; for example if a theme includes an existing settings panel for configuring colors and fonts, they may be able to use PHP to insert this configuration into the theme.json file until a global style editor is available to client users.

I would propose updating the filter to hook in at 999 which still conveys that the filter is intended to be run late while still allowing developers the option to adjust without a more complex unhook/rehook dance.

[aristath]

As far as I know, theme.json is not intended to run late, it's intended to override PHP.
The "old" method was using theme-supports which can be added at any time, anywhere. The theme.json file must override those theme-supports and therefore it must run last and not just late. I believe that's why it runs on PHP_INT_MAX...

[chrisvanpatten]

@aristath I understand conceptually why it’s running late, it just makes the upgrade path unnecessarily complex if you’re migrating from, for example, custom settings pages.

[justintadlock]

One other use case I have had in mind is add-on plugins (or even theme/child options). I'm kind of imagining scenarios where I might build a settings page for configuring certain defaults that are not covered by the Global Styles system. Being able to take custom plugin settings, hook in, and overrule theme.json values would be useful.

Is there even a hook that runs on both the front end and editor for this? I think block_editor_settings_all is just on the admin side, right?

[aristath]

I believe there are plans to filter theme.json values so it can be overridden, but this has not yet been implemented.

[overclokk]

Even if you filter the theme.json the result will be sanitized with the schema from the core, but if you only want to have a dynamic theme.json you can follow this issue #33524 where I linked a library for generating the theme.json from a PHP array.

[Soean]

I think we can close this issue:

PR: #44015
Docs: https://developer.wordpress.org/block-editor/reference-guides/filters/global-styles-filters/