Media: Enhance `wp_get_loading_optimization_attributes()` to support arbitrary context values.

The `wp_get_loading_optimization_attributes()` function, which was introduced in 6.3, based on the now deprecated `wp_get_loading_attr_default()` function introduced in 5.5, relies on a `$context` parameter based on which it may alter its behavior and the attributes returned. So far, it has only supported context values used within WordPress core.

This changeset decouples the behaviors of the function from specific contexts, allowing for more flexibility. Theme and plugin developers will be able to rely on their own context values when rendering images in non-standard ways, rather than being forced to use a core context, to get the loading optimization benefits the function provides.

As part of this change, a `wp_loading_optimization_force_header_contexts` filter is introduced, which allows filtering the map of context values and whether they should be considered header contexts, i.e. i.e. any image having one of these contexts will be assumed to appear above the fold.

Props mukesh27, costdev, flixos90.
Fixes #58894.

Built from https://develop.svn.wordpress.org/trunk@56612


git-svn-id: http://core.svn.wordpress.org/trunk@56124 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/media.php

@@ -5652,14 +5652,10 @@ function wp_get_loading_optimization_attributes( $tag_name, $attr, $context ) {
 	 * can result in the first post content image being lazy-loaded or an image further down the page being marked as a
 	 * high priority.
 	 */
-	switch ( $context ) {
+	// TODO: Handle shortcode images together with the content (see https://core.trac.wordpress.org/ticket/58853).
-		case 'the_post_thumbnail':
+	if ( 'the_content' !== $context && 'do_shortcode' !== $context && doing_filter( 'the_content' ) ) {
-		case 'wp_get_attachment_image':
-		case 'widget_media_image':
-			if ( doing_filter( 'the_content' ) ) {
 		return $loading_attrs;
 	}
-	}
 
 	/*
 	 * The key function logic starts here.
@@ -5709,19 +5705,27 @@ function wp_get_loading_optimization_attributes( $tag_name, $attr, $context ) {
 	}
 
 	if ( null === $maybe_in_viewport ) {
-		switch ( $context ) {
+		$header_enforced_contexts = array(
+			'template_part_' . WP_TEMPLATE_PART_AREA_HEADER => true,
+			'get_header_image_tag'                          => true,
+		);
+
+		/**
+		 * Filters the header-specific contexts.
+		 *
+		 * @since 6.4.0
+		 *
+		 * @param array $default_header_enforced_contexts Map of contexts for which elements should be considered
+		 *                                                in the header of the page, as $context => $enabled
+		 *                                                pairs. The $enabled should always be true.
+		 */
+		$header_enforced_contexts = apply_filters( 'wp_loading_optimization_force_header_contexts', $header_enforced_contexts );
+
 		// Consider elements with these header-specific contexts to be in viewport.
-			case 'template_part_' . WP_TEMPLATE_PART_AREA_HEADER:
+		if ( isset( $header_enforced_contexts[ $context ] ) ) {
-			case 'get_header_image_tag':
 			$maybe_in_viewport    = true;
 			$maybe_increase_count = true;
-				break;
+		} elseif ( ! is_admin() && in_the_loop() && is_main_query() ) {
-			// Count main content elements and detect whether in viewport.
-			case 'the_content':
-			case 'the_post_thumbnail':
-			case 'do_shortcode':
-				// Only elements within the main query loop have special handling.
-				if ( ! is_admin() && in_the_loop() && is_main_query() ) {
 			/*
 			 * Get the content media count, since this is a main query
 			 * content element. This is accomplished by "increasing"
@@ -5739,21 +5743,7 @@ function wp_get_loading_optimization_attributes( $tag_name, $attr, $context ) {
 			} else {
 				$maybe_in_viewport = false;
 			}
-				}
+		} elseif (
-				/*
-				 * For the 'the_post_thumbnail' context, the following case
-				 * clause needs to be considered as well, therefore skip the
-				 * break statement here if the viewport has not been
-				 * determined.
-				 */
-				if ( 'the_post_thumbnail' !== $context || null !== $maybe_in_viewport ) {
-					break;
-				}
-			// phpcs:ignore Generic.WhiteSpace.ScopeIndent.Incorrect
-			// Consider elements before the loop as being in viewport.
-			case 'wp_get_attachment_image':
-			case 'widget_media_image':
-				if (
 			// Only apply for main query but before the loop.
 			$wp_query->before_loop && $wp_query->is_main_query()
 			/*
@@ -5766,8 +5756,6 @@ function wp_get_loading_optimization_attributes( $tag_name, $attr, $context ) {
 			$maybe_in_viewport    = true;
 			$maybe_increase_count = true;
 		}
-				break;
-		}
 	}
 
 	/*

wp-includes/version.php

@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '6.4-alpha-56611';
+$wp_version = '6.4-alpha-56612';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.