preload.php

<?php

/**
 * Preload necessary resources for the editors.
 *
 * @param array                   $paths   REST API paths to preload.
 * @param WP_Block_Editor_Context $context Current block editor context
 *
 * @return array Filtered preload paths.
 */
function gutenberg_block_editor_preload_paths_6_9( $paths, $context ) {
	if ( 'core/edit-site' === $context->name ) {
		// Only prefetch for the root. If we preload it for all pages and it's not used
		// it won't be possible to invalidate.
		// To do: perhaps purge all preloaded paths when client side navigating.
		if ( isset( $_GET['p'] ) && '/' !== $_GET['p'] ) {
			$paths = array_filter(
				$paths,
				static function ( $path ) {
					return '/wp/v2/templates/lookup?slug=front-page' !== $path && '/wp/v2/templates/lookup?slug=home' !== $path;
				}
			);
		}
	}

	return $paths;
}
add_filter( 'block_editor_rest_api_preload_paths', 'gutenberg_block_editor_preload_paths_6_9', 10, 2 );

/**
 * Filters the block editor preload paths to include media processing fields.
 *
 * The packages/core-data/src/entities.js file requests additional fields
 * (image_sizes, image_size_threshold) on the root endpoint that are not
 * included in WordPress Core's default preload paths. This filter ensures
 * the preloaded URL matches exactly what the JavaScript requests.
 *
 * @since 20.1.0
 *
 * @param array $paths REST API paths to preload.
 * @return array Filtered preload paths.
 */
function gutenberg_block_editor_preload_paths_root_fields( $paths ) {
	// Complete list of fields expected by packages/core-data/src/entities.js.
	// This must match exactly for preloading to work (same fields, same order).
	// @see packages/core-data/src/entities.js rootEntitiesConfig.__unstableBase
	$root_fields = 'description,gmt_offset,home,image_sizes,image_size_threshold,name,site_icon,site_icon_url,site_logo,timezone_string,url,page_for_posts,page_on_front,show_on_front';

	foreach ( $paths as $key => $path ) {
		if ( is_string( $path ) && str_starts_with( $path, '/?_fields=' ) ) {
			// Replace with the complete fields list to ensure exact match.
			$paths[ $key ] = '/?_fields=' . $root_fields;
			break;
		}
	}

	return $paths;
}
add_filter( 'block_editor_rest_api_preload_paths', 'gutenberg_block_editor_preload_paths_root_fields' );

/**
 * Preload bound single-resource GETs the post editor would otherwise
 * fetch post-mount.
 *
 * @param array                   $paths   REST API paths.
 * @param WP_Block_Editor_Context $context Block editor context.
 * @return array
 */
function gutenberg_block_editor_preload_paths_post_editor_bound_gets( $paths, $context ) {
	if ( 'core/edit-post' !== $context->name || ! isset( $context->post ) ) {
		return $paths;
	}
	$paths[] = '/wp/v2/templates/lookup?slug=front-page';
	$paths[] = '/wp/v2/taxonomies?context=edit';
	$paths[] = array( '/wp/v2/posts', 'OPTIONS' );

	$author_id = (int) get_post_field( 'post_author', $context->post->ID );
	if ( $author_id ) {
		$paths[] = sprintf(
			'/wp/v2/users/%d?context=view&_fields=id,name',
			$author_id
		);
	}

	return $paths;
}
add_filter( 'block_editor_rest_api_preload_paths', 'gutenberg_block_editor_preload_paths_post_editor_bound_gets', 10, 2 );