增加requireCallback验证规则

library/think/Loader.php

@@ -337,9 +337,6 @@ class Loader
             $module = APP_MULTI_MODULE ? MODULE_NAME : '';
         }
         $class = self::parseClass($module, $layer, $name);
-        // controller_load
-        APP_HOOK && Hook::listen('controller_load', $class);
-
         if (class_exists($class)) {
             $action                    = new $class;
             $_instance[$name . $layer] = $action;

library/think/Validate.php

@@ -665,6 +665,24 @@ class Validate
         }
     }
 
+    /**
+     * 通过回调方法验证某个字段是否必须
+     * @access protected
+     * @param mixed $value  字段值
+     * @param mixed $rule  验证规则
+     * @param array $data  数据
+     * @return bool
+     */
+    protected function requireCallback($value, $rule, $data)
+    {
+        $result = call_user_func_array($rule, [$value, $data]);
+        if ($result) {
+            return !empty($value);
+        } else {
+            return true;
+        }
+    }
+
     /**
      * 验证某个字段有值的情况下必须
      * @access protected