--wp--preset-- variables defaults not being updated by add_theme_support() 'editor-font-sizes' or 'editor-color-palette'

[tommusrhodus]

Having an issue updating the default values for preset variables, such as font size large, or color black

Since 5.9 it appears that fonts and colours defined in theme.json will correctly override the default values of --wp--preset-- variables, however those defined via add_theme_support are not, and so the default values are still being used.

This is being triggered by whether or not a theme calls add_theme_support( 'experimental-link-color' )

A simple way to test what's going on here:

1. Open a blank install with the Twenty-Twenty-One theme installed.
2. Create a new page and add paragraph text with the font size set to large and set the background color to black
3. Open functions.php and edit line 170 to change the large font size, and then edit line 203 to change the black color and save.

Result: Paragraph text correctly reflects changes made to font size and color.

4. Open functions.php and delete line 333: add_theme_support( 'experimental-link-color' );

Result: Font size and color fallback to WP default values.

Expected behaviour: Font sizes and colors set via add_theme_support should continue to work as pre 5.9 without the need to add add_theme_support( 'experimental-link-color' );

[billerickson]

Here's a related ticket I posted on the Gutenberg GitHub repo: ​https://github.com/WordPress/gutenberg/issues/38252

In WordPress 5.9, only font sizes & colors defined in theme.json will take precedence over WordPress' core global styles with the same name. This is an issue.

At a minimum, in themes that do not have a theme.json file, the font sizes defined in add_theme_support( 'editor-font-sizes' ) should take precedence over the WordPress core global styles with the same name.

A better approach would be to limit the new style updates (and aggressive use of !important) to themes that use theme.json, in the same way that we limit other breaking changes in Gutenberg to themes with a theme.json file (ex: removing the .wp-block-groupinner-container from groups).

[tommusrhodus]

I have tracked down the issue to wp_get_global_stylesheet() ​https://github.com/tommusrhodus/WordPress/blob/master/wp-includes/global-styles-and-settings.php#L107-L117

In the above lines, the function checks if the theme has theme.json and if it declares add_theme_support( 'experimental-link-color' ), if a theme does neither the function does not merge the theme variables into the default variables.

The result is that theme declared variables which share names with WP Presets, do not overwrite those presets unless add_theme_support( 'experimental-link-color' ) is declared in the theme.

Since 5.9 it appears that fonts and colours defined in theme.json will correctly override the default values of --wp--preset-- variables, however those defined via add_theme_support are not, and so the default values are still being used.

This is being triggered by whether or not a theme calls add_theme_support( 'experimental-link-color' )

A simple way to test what's going on here:

1. Open a blank install with the Twenty-Twenty-One theme installed.
2. Create a new page and add paragraph text with the font size set to large and set the background color to black
3. Open functions.php and edit line 170 to change the large font size, and then edit line 203 to change the black color and save.

Result: Paragraph text correctly reflects changes made to font size and color.

4. Open functions.php and delete line 333: add_theme_support( 'experimental-link-color' );

Result: Font size and color fallback to WP default values.

Expected behaviour: Font sizes and colors set via add_theme_support should continue to work as pre 5.9 without the need to add add_theme_support( 'experimental-link-color' ); or theme.json

This PR removes experimental-link-color dependancy in wp-includes/global-styles-and-settings.php for themes to be able to update --wp--preset variables without the need to setup theme.json or add theme support for an experimental feature.

Trac ticket: https://core.trac.wordpress.org/ticket/54954