Replacing hard-coded style tags with wp_add_inline_style()

This dev note highlights the changes made in WordPress 6.4 to style loading. The main focus of the changes was to replace manually created style tags printed at the wp_head action with calls to wp_add_inline_style(). This change was implemented to address issues related to redundant code and bypassing the core’s style enqueuing system, which made it challenging for third-party developers to manage and control the output of style tags.

Deprecated Functions

To maintain backward compatibility, the following functions have been deprecated and replaced with the new approach:

  • print_embed_styles()
  • print_emoji_styles()
  • wp_admin_bar_header()
  • _admin_bar_bump_cb()
  • the_block_template_skip_link()

Backwards Compatibility Unhooking

Previously, when wanting to unhook certain functions like print_embed_styles() from happening at wp_print_styles(),

a theme or plugin would do:
remove_action( 'wp_print_styles', 'print_emoji_styles' );

In 6.4 this print_emoji_styles() function is now deprecated. Nevertheless, the above method for preventing emoji styles from being printed is retained, even though they are now being printed by wp_enqueue_emoji_styles(). This applies to the other deprecated functions as well, so no developer action is required.

Developer Action Required

For developers who are currently using the wp_print_styles() function, whether it’s in unit tests or within their own code, some adjustments may be necessary to ensure a smooth transition. You should follow the example set by Gutenberg. This is what you need to do:

/**
 * Remove the deprecated `print_emoji_styles` handler.
 * It avoids breaking style generation with a deprecation message.
 */
$has_emoji_styles = has_action( 'wp_print_styles', 'print_emoji_styles' );
if ( $has_emoji_styles ) {
    remove_action( 'wp_print_styles', 'print_emoji_styles' );
}

ob_start();
wp_print_styles();
$styles = ob_get_clean();

if ( $has_emoji_styles ) {
    add_action( 'wp_print_styles', 'print_emoji_styles' );
}

This code snippet demonstrates how to handle the situation. It first checks if there’s an action hooked to wp_print_styles for print_emoji_styles(). If it does exist, it removes the action temporarily to avoid issues with style generation.

By following this approach, you can ensure that your code remains compatible with the changes introduced in this commit while avoiding any disruptions to style generation. It’s recommended to review and adjust your code accordingly if you’ve been using the wp_print_styles() function.

Exceptions

In the case of the functions for printing custom backgrounds and custom styles, converting them to use inline styles was deemed infeasible. Changing the style tag IDs in this context could potentially disrupt JavaScript functionality for several plugins in the repository. Therefore, these functions remain unaffected by this change.

Please refer to #58775 for additional details on these changes.

Props to @spacedmonkey for writing the dev note.
Props to @westonruter, @flixos90, @webcommsat, and @bph for review and proofreading.

#6-4, #dev-notes, #dev-notes-6-4, #performance

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