Responsive Images: limit the size of images included in `srcset` attributes. Introduce `max_srcset_image_width` filter to adjust the limit.

Props joemcgill.
Fixes #34341.
Built from https://develop.svn.wordpress.org/trunk@35358


git-svn-id: http://core.svn.wordpress.org/trunk@35324 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/media.php

@@ -928,6 +928,15 @@ function wp_get_attachment_image_srcset_array( $attachment_id, $size = 'medium'
 	 */
 	$img_edited = preg_match( '/-e[0-9]{13}/', $img_url, $img_edit_hash );
 
+	/**
+	 * Filter the maximum width included in a srcset attribute.
+	 *
+	 * @since 4.4.0
+	 *
+	 * @param array|string $size Size of image, either array or string.
+	 */
+	$max_srcset_width = apply_filters( 'max_srcset_image_width', 1600, $size );
+
 	/*
 	 * Set up arrays to hold url candidates and matched image sources so
 	 * we can avoid duplicates without looping through the full sources array
@@ -945,6 +954,11 @@ function wp_get_attachment_image_srcset_array( $attachment_id, $size = 'medium'
 			continue;
 		}
 
+		// Filter out images that are wider than $max_srcset_width.
+		if ( $max_srcset_width && $img['width'] > $max_srcset_width ) {
+			$contiue;
+		}
+
 		$candidate_url = path_join( dirname( $img_url ), $img['file'] );
 
 		// Calculate the new image ratio.

wp-includes/version.php

@@ -4,7 +4,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '4.4-alpha-35357';
+$wp_version = '4.4-alpha-35358';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.