Avoid treating fetchpriority=auto as maybe_in_viewport and prevent incrementing media count for them

Author: westonruter

src/wp-includes/media.php

@@ -6115,7 +6115,6 @@ function wp_get_loading_optimization_attributes( $tag_name, $attr, $context ) {
 		 * on an IMG following any number of initial IMGs with `fetchpriority=auto` since those initial images may not
 		 * be displayed.
 		 */
-		$maybe_in_viewport = true;
 
 		// Preserve fetchpriority=auto.
 		$loading_attrs['fetchpriority'] = 'auto';
@@ -6195,16 +6194,20 @@ function wp_get_loading_optimization_attributes( $tag_name, $attr, $context ) {
 	/*
 	 * If flag was set based on contextual logic above, increase the content
 	 * media count, either unconditionally, or based on whether the image size
-	 * is larger than the threshold.
+	 * is larger than the threshold. This does not apply when the IMG has
+	 * fetchpriority=auto because it may be conditionally displayed by viewport
+	 * size.
 	 */
-	if ( $increase_count ) {
-		wp_increase_content_media_count();
-	} elseif ( $maybe_increase_count ) {
-		/** This filter is documented in wp-includes/media.php */
-		$wp_min_priority_img_pixels = apply_filters( 'wp_min_priority_img_pixels', 50000 );
-
-		if ( $wp_min_priority_img_pixels <= $attr['width'] * $attr['height'] ) {
+	if ( 'auto' !== $existing_fetchpriority ) {
+		if ( $increase_count ) {
 			wp_increase_content_media_count();
+		} elseif ( $maybe_increase_count ) {
+			/** This filter is documented in wp-includes/media.php */
+			$wp_min_priority_img_pixels = apply_filters( 'wp_min_priority_img_pixels', 50000 );
+
+			if ( $wp_min_priority_img_pixels <= $attr['width'] * $attr['height'] ) {
+				wp_increase_content_media_count();
+			}
 		}
 	}
 

tests/phpunit/tests/media.php

@@ -4726,6 +4726,20 @@ public function test_wp_get_loading_optimization_attributes_with_fetchpriority_a
 			);
 
 			$this->assert_fetchpriority_low_loading_attrs( $attr, $context );
+
+			$this->assertSameSetsWithIndex(
+				array(
+					'decoding'      => 'async',
+					'fetchpriority' => 'auto',
+					'loading'       => 'lazy',
+				),
+				wp_get_loading_optimization_attributes(
+					'img',
+					array_merge( $attr, array( 'fetchpriority' => 'auto' ) ),
+					$context
+				),
+				'Expected a fetchpriority=auto IMG appearing after the media count threshold to till be lazy-loaded.'
+			);
 		}
 	}