Consider allowing themes to opt in to wp-block-styles via theme.json

[kjellr]

wp-block-styles was considered and removed from #35593, as per @jasmussen's comment here.

This seems ok to omit by default, but I do think it would be helpful for themes to have the option of using theme.json to opt into this feature in general. Currently, they must do so via add_theme_support(). Currently, this is the only theme support call that Twenty Twenty-Two needs to make, and it would be great to migrate that over to theme.json.

[zaguiini]

It would be awesome if Gutenberg by itself figured out which styles it needs based on block usage and loaded them on demand.

Example: I'm using the Image block. It makes sense to include the Image styles, while still not needing to load all the other styles.

[chthonic-ds]

@zaguiini this has been possible since WP 5.8, more info here: https://make.wordpress.org/core/2021/07/01/block-styles-loading-enhancements-in-wordpress-5-8/. It's still required for a theme to opt in as of WP 5.9beta2 but #35593 (comment) suggests it will eventually be enabled by default.

[scruffian]

Fixed by #40097

[scruffian]

After a chat with @mtias we decided that this isn't the right approach. Instead we should move this CSS to Global Styles, and then build a mechanism to disable the core theme.json file:

#33977
#40181

This would render the wp-block-styles theme support obsolete.

[mtias]

wp.block-styles predates many of the block attribute tools and as such is a very opaque system. In time, things we expressed in the stylesheet should become part of the theme.json toolset (styling captions as elements.caption, specifying default views for blocks like Quote, etc). At that point an extra stylesheet is unnecessary and inconvenient, and absorbing its properties into attributes is much more flexible.