phan: update Less_Tree_Variable::compile() return types

The Variable::compile() can return different subtypes of
Less_Tree. In mentioned specified scenario it can return
Less_Tree_Keyword or Less_Tree_Quoted, therefore the node
will have always have the $value property.
To satisfy phan, it's good enough to add additional
possible return types to @return statemenmt.

Bug: T327082
Change-Id: I412dfd2258a7352e2d8a03e5dc187b53ebf3c843

lib/Less/Tree/Variable.php

@@ -20,16 +20,14 @@ public function __construct( $name, $index = null, $currentFileInfo = null ) {
 
 	/**
 	 * @param Less_Environment $env
-	 * @return Less_Tree
+	 * @return Less_Tree|Less_Tree_Keyword|Less_Tree_Quoted
 	 * @see less-2.5.3.js#Ruleset.prototype.eval
 	 */
 	public function compile( $env ) {
 		if ( $this->name[1] === '@' ) {
 			$v = new self( substr( $this->name, 1 ), $this->index + 1, $this->currentFileInfo );
-			// While some Less_Tree nodes have no 'value', we know these can't ocurr after a variable
-			// assignment (would have been a ParseError).
-			// TODO: Solve better (https://phabricator.wikimedia.org/T327082).
-			// @phan-suppress-next-line PhanUndeclaredProperty
+			// While some Less_Tree nodes have no 'value', we know these can't occur after a
+			// variable assignment (would have been a ParseError).
 			$name = '@' . $v->compile( $env )->value;
 		} else {
 			$name = $this->name;