Add stat() options to ProductionFilesystemLoader

* By default, continue to use `size` and `mtime` to invalidate template cache
 * Allow overriding to use any properties of `stat()`
 * Allow disabling stat entirely 
 * Add a Big Kid Pants disclaimer if you choose to go down this path

src/Mustache/Loader/ProductionFilesystemLoader.php

@@ -18,6 +18,52 @@
  */
 class Mustache_Loader_ProductionFilesystemLoader extends Mustache_Loader_FilesystemLoader
 {
+    private $statProps;
+
+    /**
+     * Mustache production filesystem Loader constructor.
+     *
+     * Passing an $options array allows overriding certain Loader options during instantiation:
+     *
+     *     $options = array(
+     *         // The filename extension used for Mustache templates. Defaults to '.mustache'
+     *         'extension' => '.ms',
+     *         'stat_props' => array('size', 'mtime'),
+     *     );
+     *
+     * Specifying 'stat_props' overrides the stat properties used to invalidate the template cache. By default, this
+     * uses 'mtime' and 'size', but this can be set to any of the properties supported by stat():
+     *
+     *     http://php.net/manual/en/function.stat.php
+     *
+     * You can also disable filesystem stat entirely:
+     *
+     *     $options = array('stat_props' => null);
+     *
+     * But with great power comes great responsibility. Namely, if you disable stat-based cache invalidation,
+     * YOU MUST CLEAR THE TEMPLATE CACHE YOURSELF when your templates change. Make it part of your build or deploy
+     * process so you don't forget!
+     *
+     * @throws Mustache_Exception_RuntimeException if $baseDir does not exist.
+     *
+     * @param string $baseDir Base directory containing Mustache template files.
+     * @param array  $options Array of Loader options (default: array())
+     */
+    public function __construct($baseDir, array $options = array())
+    {
+        parent::__construct($baseDir, $options);
+
+        if (array_key_exists('stat_props', $options)) {
+            if (empty($options['stat_props'])) {
+                $this->statProps = array();
+            } else {
+                $this->statProps = $options['stat_props'];
+            }
+        } else {
+            $this->statProps = array('size', 'mtime');
+        }
+    }
+
     /**
      * Helper function for loading a Mustache file by name.
      *
@@ -35,6 +81,6 @@ class Mustache_Loader_ProductionFilesystemLoader extends Mustache_Loader_Filesys
             throw new Mustache_Exception_UnknownTemplateException($name);
         }
 
-        return new Mustache_Source_FilesystemSource($fileName);
+        return new Mustache_Source_FilesystemSource($fileName, $this->statProps);
     }
 }

src/Mustache/Source/FilesystemSource.php

@@ -19,17 +19,20 @@
  */
 class Mustache_Source_FilesystemSource implements Mustache_Source
 {
-    private $stat;
     private $filename;
+    private $statProps;
+    private $stat;
 
     /**
      * Filesystem Source constructor.
      *
      * @param string $filename
+     * @param array  $statProps
      */
-    public function __construct($filename)
+    public function __construct($filename, array $statProps)
     {
         $this->filename = $filename;
+        $this->statProps = $statProps;
     }
 
     /**
@@ -41,6 +44,11 @@ class Mustache_Source_FilesystemSource implements Mustache_Source
      */
     public function getKey()
     {
+        $chunks = array(
+            sprintf('filename:%s', $this->filename),
+        );
+
+        if (!empty($this->statProps)) {
             if (!isset($this->stat)) {
                 $this->stat = stat($this->filename);
             }
@@ -49,7 +57,12 @@ class Mustache_Source_FilesystemSource implements Mustache_Source
                 throw new RuntimeException(sprintf('Failed to read source file "%s".', $this->filename));
             }
 
-        return sprintf('filename:%s,size:%s,mtime:%s', $this->filename, $this->stat['size'], $this->stat['mtime']);
+            foreach ($this->statProps as $prop) {
+                $chunks[] = sprintf('%s:%s', $prop, $this->stat[$prop]);
+            }
+        }
+
+        return implode(',', $chunks);
     }
 
     /**