Media: Add "loading" as an allowed kses image attribute

With loading="lazy" being added to all images in [47554], let's ensure that it passes kses attributes too.

Fixes #50731.
Props TimothyBlynJacobs, peterwilsoncc, azaozz. 



git-svn-id: https://develop.svn.wordpress.org/trunk@48572 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/kses.php

@@ -230,6 +230,7 @@ if ( ! CUSTOM_TAGS ) {
 			'border'   => true,
 			'height'   => true,
 			'hspace'   => true,
+			'loading'  => true,
 			'longdesc' => true,
 			'vspace'   => true,
 			'src'      => true,

tests/phpunit/tests/kses.php

@@ -765,6 +765,11 @@ EOF;
 				'src="mypic.jpg"',
 				'src="mypic.jpg"',
 			),
+			array(
+				'img',
+				'loading="lazy"',
+				'loading="lazy"',
+			),
 			array(
 				'img',
 				'onerror=alert(1)',
@@ -1352,4 +1357,26 @@ EOF;
 			),
 		);
 	}
+
+	/**
+	 * Test filtering a standard img tag.
+	 *
+	 * @ticket 50731
+	 */
+	function test_wp_kses_img_tag_standard_attributes() {
+		$html = array(
+			'<img',
+			'loading="lazy"',
+			'src="https://example.com/img.jpg"',
+			'width="1000"',
+			'height="1000"',
+			'alt=""',
+			'class="wp-image-1000"',
+			'/>',
+		);
+
+		$html = implode( ' ', $html );
+
+		$this->assertSame( $html, wp_kses_post( $html ) );
+	}
 }