Allow identification of links to non-existing pages

An extra class is added to generated links:
- "wikilink1" for links to existing pages
- "wikilink2" for links to new pages

MenuItem.php

@@ -68,4 +68,26 @@ class MenuItem extends AbstractItem {
 		$this->id = implode(':', array_merge($target_path, $page_path));
 		$this->params = [];
 	}
+
+	/**
+	 * Convenience method to get the attributes for constructing an <a> element
+	 * Parent method is declared in dokuwiki\Menu\Item\AbstractItem
+	 *
+	 * @param  string|false $classprefix create a class from type with this prefix, false for no class
+	 *
+	 * @return array
+	 */
+	public function getLinkAttributes($classprefix = 'menuitem ') : array {
+		$attributes = parent::getLinkAttributes($classprefix);
+		// Get already set classes, defaulting to an empty string
+		$classes = ( isset($attributes['class']) ) ?
+			$attributes['class'] : '';
+		// Add an extra class, based on the existence of the target page
+		$extra_class = ( page_exists($this->id) ) ?
+			'wikilink1' : 'wikilink2';
+		$classes = trim("$classes $extra_class");
+		// Return the full attributes list, including the updated classes list
+		$attributes['class'] = $classes;
+		return $attributes;
+	}
 }