Token-like patterns no longer treated as templates

src/PatternLab/PatternEngine/Twig/Loaders/PatternLoader.php

@@ -84,7 +84,7 @@ public function __construct($options = array()) {
 		// 3. add String loader
 		// This *must* go last or no loaders after will work ~ https://github.com/symfony/symfony/issues/10865
 		// @todo Remove `Twig_Loader_String` - if a Twig include path is wrong, this outputs the string anyway with no error ~ https://github.com/symfony/symfony/issues/10865
-		$loaders[] = new \Twig_Loader_String();
+		$loaders[] = new Twig\ConditionalStringLoader();
 
 		// set-up Twig
 		$twigLoader = new \Twig_Loader_Chain($loaders);

src/PatternLab/PatternEngine/Twig/Loaders/StringLoader.php

@@ -48,7 +48,7 @@ public function __construct($options = array()) {
 		if (count($filesystemLoaderPaths) > 0) {
 			$loaders[] = new \Twig_Loader_Filesystem($filesystemLoaderPaths);
 		}
-		$loaders[] = new \Twig_Loader_String();
+		$loaders[] = new Twig\ConditionalStringLoader();
 
 		// set-up Twig
 		$twigLoader = new \Twig_Loader_Chain($loaders);

src/PatternLab/PatternEngine/Twig/Loaders/Twig/ConditionalStringLoader.php

@@ -0,0 +1,31 @@
+<?php
+
+/*!
+ * Copyright (c) 2016 Erik Mogensen
+ * Licensed under the MIT license
+ */
+
+namespace PatternLab\PatternEngine\Twig\Loaders\Twig;
+
+class ConditionalStringLoader extends \Twig_Loader_String {
+
+	/**
+	 * Return the source context if and only if it exists.
+	 */
+	public function getSourceContext($name) {
+		if ($this->exists($name)) {
+			 return parent::getSourceContext($name);
+		}
+		return null;
+	}
+
+	/**
+	 * Return false if $name looks like a simple file name, true otherwise.
+	 *
+	 * A simple file name is a simple string consisting of alphanumerics,
+	 * periods, hyphens, underbars, and so on,  otherwise
+	 */
+	public function exists($name) {
+		return preg_match("/^[-a-zA-Z0-9~\\.\\/_@]+$/", $name) === 0;
+	}
+}