Fix bug in the WordPress Customizer preview related to the CSS classes of a menu item

Author: Luciano van der Veekens

class-wp-bootstrap-navwalker.php

@@ -105,6 +105,13 @@ public function start_el( &$output, $item, $depth = 0, $args = array(), $id = 0
 
 			$classes = empty( $item->classes ) ? array() : (array) $item->classes;
 
+			// Updating the CSS classes of a menu item in the WordPress Customizer preview results in all classes defined
+			// in that particular input box to come in as one big class string.
+			$split_on_spaces = function ( $class ) {
+				return preg_split( '/\s+/', $class );
+			};
+			$classes         = flatten( array_map( $split_on_spaces, $classes ) );
+
 			// Initialize some holder variables to store specially handled item
 			// wrappers and icons.
 			$linkmod_classes = array();
@@ -552,4 +559,23 @@ private function linkmod_element_close( $linkmod_type ) {
 			return $output;
 		}
 	}
+
+	/**
+	 * Flattens a multidimensional array to a simple array.
+	 *
+	 * @param array $array a multidimensional array.
+	 *
+	 * @return array a simple array
+	 */
+	function flatten( $array ) {
+		$result = array();
+		foreach ( $array as $element ) {
+			if ( is_array( $element ) ) {
+				array_push( $result, ...flatten( $element ) );
+			} else {
+				$result[] = $element;
+			}
+		}
+		return $result;
+	}
 }