Register wp-theme design tokens stylesheet

[roshniahuja]

Trac ticket

Fixes https://core.trac.wordpress.org/ticket/65646

Summary

The wp-theme JS package is registered in Core, but its accompanying design tokens stylesheet was only registered in the Gutenberg plugin. Without the stylesheet, token-consuming styles may see undefined values. Although first-party usage injects fallback values at build time, the intended behaviour is that the design tokens stylesheet is actually loaded wherever design tokens are used.

Changes

In wp_default_styles():

• Register a theme package style pointing to /wp-includes/css/dist/theme/design-tokens$suffix.css (special-cased like base-styles, since the filename is not the default style.css).
• Add wp-theme as a dependency of wp-components so token values are defined before the consuming styles reference them.
• Load wp-theme first among the editor (wp-edit-blocks) dependencies, and add it to the RTL styles list for consistency with the other package styles.

This mirrors the Gutenberg plugin setup.

Unit tests were added to tests/phpunit/tests/dependencies/styles.php covering registration of the handle/src, the wp-components dependency, and the editor style ordering.

Note for reviewers

The registered file css/dist/theme/design-tokens.css is synced from the Gutenberg build (like all other css/dist/* assets), so a Gutenberg version bump that outputs the theme/ styles directory must precede or accompany this change. Until then the handle resolves to a file that is not yet present in Core.

Testing instructions

1. Run the dependency tests: phpunit tests/phpunit/tests/dependencies/styles.php.
2. Confirm the wp-theme handle is registered and that wp-components and wp-edit-blocks depend on it.

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