Layout: backport fix to ensure blocks without layout support do not receive layout classnames

src/wp-includes/block-supports/layout.php

@@ -615,6 +615,9 @@ function wp_render_layout_support_flag( $block_content, $block ) {
 			$processor->add_class( $class_name );
 		}
 		return $processor->get_updated_html();
+	} elseif ( ! $block_supports_layout ) {
+		// Ensure layout classnames are not injected if there is no layout support.
+		return $block_content;
 	}
 
 	$global_settings = wp_get_global_settings();

tests/phpunit/tests/block-supports/layout.php

@@ -171,6 +171,7 @@ public function test_outer_container_not_restored_for_aligned_image_block_with_t
 	/**
 	 * @ticket 57584
 	 * @ticket 58548
+	 * @ticket 60292
 	 *
 	 * @dataProvider data_layout_support_flag_renders_classnames_on_wrapper
 	 *
@@ -250,6 +251,25 @@ public function data_layout_support_flag_renders_classnames_on_wrapper() {
 				),
 				'expected_output' => '<div class="wp-block-group"><div class="wp-block-group__inner-wrapper is-layout-flow wp-block-group-is-layout-flow"></div></div>',
 			),
+			'skip classname output if block does not support layout and there are no child layout classes to be output' => array(
+				'args'            => array(
+					'block_content' => '<p>A paragraph</p>',
+					'block'         => array(
+						'blockName'    => 'core/paragraph',
+						'attrs'        => array(
+							'style' => array(
+								'layout' => array(
+									'selfStretch' => 'fit',
+								),
+							),
+						),
+						'innerBlocks'  => array(),
+						'innerHTML'    => '<p>A paragraph</p>',
+						'innerContent' => array( '<p>A paragraph</p>' ),
+					),
+				),
+				'expected_output' => '<p>A paragraph</p>',
+			),
 		);
 	}