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<title>[55825] trunk: Media: Prevent special images within post content to skew image counts and cause lazy-loading bugs.</title>
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<dt style="float: left; width: 6em; font-weight: bold">Revision</dt> <dd><a style="font-weight: bold" href="https://core.trac.wordpress.org/changeset/55825">55825</a><script type="application/ld+json">{"@context":"http://schema.org","@type":"EmailMessage","description":"Review this Commit","action":{"@type":"ViewAction","url":"https://core.trac.wordpress.org/changeset/55825","name":"Review Commit"}}</script></dd>
<dt style="float: left; width: 6em; font-weight: bold">Author</dt> <dd>flixos90</dd>
<dt style="float: left; width: 6em; font-weight: bold">Date</dt> <dd>2023-05-18 19:53:37 +0000 (Thu, 18 May 2023)</dd>
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<pre style='padding-left: 1em; margin: 2em 0; border-left: 2px solid #ccc; line-height: 1.25; font-size: 105%; font-family: sans-serif'>Media: Prevent special images within post content to skew image counts and cause lazy-loading bugs.
In order to skip lazy-loading the first few images on a page, as of WordPress 5.9 there has been logic to count images that are eligible based on certain criteria. One of those groups are images that appear within the content of a post.
This changeset fixes a bug where images created via `get_the_post_thumbnail()` or `wp_get_attachment_image()` that are injected into the post content would skew the count and therefore result in all images to be lazy-loaded, potentially hurting load time performance. This is relevant for example when those functions are called in server-side rendered blocks, or any other filter callbacks hooked into `the_content`.
Props flixos90, antpb, joedolson, spacedmonkey, mukesh27, thekt12, costdev, jrf.
Fixes <a href="https://core.trac.wordpress.org/ticket/58089">#58089</a>.
See <a href="https://core.trac.wordpress.org/ticket/53675">#53675</a>.</pre>
<h3>Modified Paths</h3>
<ul>
<li><a href="#trunksrcwpincludesmediaphp">trunk/src/wp-includes/media.php</a></li>
<li><a href="#trunktestsphpunittestsmediaphp">trunk/tests/phpunit/tests/media.php</a></li>
</ul>
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<h3>Diff</h3>
<a id="trunksrcwpincludesmediaphp"></a>
<div class="modfile"><h4 style="background-color: #eee; color: inherit; margin: 1em 0; padding: 1.3em; font-size: 115%">Modified: trunk/src/wp-includes/media.php</h4>
<pre class="diff"><span>
<span class="info" style="display: block; padding: 0 10px; color: #888">--- trunk/src/wp-includes/media.php 2023-05-18 12:34:22 UTC (rev 55824)
+++ trunk/src/wp-includes/media.php 2023-05-18 19:53:37 UTC (rev 55825)
</span><span class="lines" style="display: block; padding: 0 10px; color: #888">@@ -5507,6 +5507,16 @@
</span><span class="cx" style="display: block; padding: 0 10px"> }
</span><span class="cx" style="display: block; padding: 0 10px">
</span><span class="cx" style="display: block; padding: 0 10px"> /*
</span><ins style="background-color: #dfd; text-decoration:none; display:block; padding: 0 10px">+ * Skip programmatically created images within post content as they need to be handled together with the other
+ * images within the post content.
+ * Without this clause, they would already be counted below which skews the number and can result in the first
+ * post content image being lazy-loaded only because there are images elsewhere in the post content.
+ */
+ if ( ( 'the_post_thumbnail' === $context || 'wp_get_attachment_image' === $context ) && doing_filter( 'the_content' ) ) {
+ return false;
+ }
+
+ /*
</ins><span class="cx" style="display: block; padding: 0 10px"> * The first elements in 'the_content' or 'the_post_thumbnail' should not be lazy-loaded,
</span><span class="cx" style="display: block; padding: 0 10px"> * as they are likely above the fold.
</span><span class="cx" style="display: block; padding: 0 10px"> */
</span></span></pre></div>
<a id="trunktestsphpunittestsmediaphp"></a>
<div class="modfile"><h4 style="background-color: #eee; color: inherit; margin: 1em 0; padding: 1.3em; font-size: 115%">Modified: trunk/tests/phpunit/tests/media.php</h4>
<pre class="diff"><span>
<span class="info" style="display: block; padding: 0 10px; color: #888">--- trunk/tests/phpunit/tests/media.php 2023-05-18 12:34:22 UTC (rev 55824)
+++ trunk/tests/phpunit/tests/media.php 2023-05-18 19:53:37 UTC (rev 55825)
</span><span class="lines" style="display: block; padding: 0 10px; color: #888">@@ -3853,6 +3853,101 @@
</span><span class="cx" style="display: block; padding: 0 10px"> $this->assertSame( '<div class="wp-site-blocks">' . $expected_template_content . '</div>', $html );
</span><span class="cx" style="display: block; padding: 0 10px"> }
</span><span class="cx" style="display: block; padding: 0 10px">
</span><ins style="background-color: #dfd; text-decoration:none; display:block; padding: 0 10px">+ /**
+ * @ticket 58089
+ *
+ * @covers ::wp_filter_content_tags
+ * @covers ::wp_get_loading_attr_default
+ */
+ public function test_wp_filter_content_tags_does_not_lazy_load_special_images_within_the_content() {
+ global $wp_query, $wp_the_query;
+
+ // Force no lazy-loading on the image tag expected in the content.
+ $expected_content = wpautop( wp_get_attachment_image( self::$large_id, 'large', false, array( 'loading' => false ) ) );
+
+ // Overwrite post content with an image.
+ add_filter(
+ 'the_content',
+ static function() {
+ // Replace content with an image tag, i.e. the 'wp_get_attachment_image' context is used while running 'the_content' filter.
+ return wp_get_attachment_image( self::$large_id, 'large', false );
+ },
+ 9 // Run before wp_filter_content_tags().
+ );
+
+ /*
+ * We have to run a main query loop so that the first 'the_content' context image is not
+ * lazy-loaded.
+ * Without the fix from 58089, the image would still be lazy-loaded since the check for the
+ * separately invoked 'wp_get_attachment_image' context would lead to that.
+ */
+ $wp_query = new WP_Query( array( 'post__in' => array( self::$post_ids['publish'] ) ) );
+ $wp_the_query = $wp_query;
+ $this->reset_content_media_count();
+ $this->reset_omit_loading_attr_filter();
+ $content = '';
+ while ( have_posts() ) {
+ the_post();
+ $content = get_echo( 'the_content' );
+ }
+
+ // Ensure that parsed content has the image without lazy-loading.
+ $this->assertSame( $expected_content, $content );
+ }
+
+ /**
+ * Tests that wp_get_loading_attr_default() returns 'lazy' for special contexts when they're used outside of 'the_content' filter.
+ *
+ * @ticket 58089
+ *
+ * @covers ::wp_get_loading_attr_default
+ *
+ * @dataProvider data_special_contexts_for_the_content
+ *
+ * @param string $context Context for the element for which the `loading` attribute value is requested.
+ */
+ public function test_wp_get_loading_attr_default_should_return_lazy_for_special_contexts_outside_of_the_content( $context ) {
+ $this->assertSame( 'lazy', wp_get_loading_attr_default( $context ) );
+ }
+
+ /**
+ * Tests that wp_get_loading_attr_default() returns false for special contexts when they're used within 'the_content' filter.
+ *
+ * @ticket 58089
+ *
+ * @covers ::wp_get_loading_attr_default
+ *
+ * @dataProvider data_special_contexts_for_the_content
+ *
+ * @param string $context Context for the element for which the `loading` attribute value is requested.
+ */
+ public function test_wp_get_loading_attr_default_should_return_false_for_special_contexts_within_the_content( $context ) {
+ remove_all_filters( 'the_content' );
+
+ $result = null;
+ add_filter(
+ 'the_content',
+ function( $content ) use ( &$result, $context ) {
+ $result = wp_get_loading_attr_default( $context );
+ return $content;
+ }
+ );
+ apply_filters( 'the_content', '' );
+ $this->assertFalse( $result );
+ }
+
+ /**
+ * Data provider.
+ *
+ * @return array[]
+ */
+ public function data_special_contexts_for_the_content() {
+ return array(
+ 'the_post_thumbnail' => array( 'context' => 'the_post_thumbnail' ),
+ 'wp_get_attachment_image' => array( 'context' => 'wp_get_attachment_image' ),
+ );
+ }
+
</ins><span class="cx" style="display: block; padding: 0 10px"> private function reset_content_media_count() {
</span><span class="cx" style="display: block; padding: 0 10px"> // Get current value without increasing.
</span><span class="cx" style="display: block; padding: 0 10px"> $content_media_count = wp_increase_content_media_count( 0 );
</span></span></pre>
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