Ticket #24205: 24205.2.patch

plugin.php

@@ -432 +432 @@
  * @since 2.5.0
  *
  * @param string $plugin Base plugin path from plugins directory.
+ * @param bool $check_all Defaults true. On true, checks mu-plugins and dropins for existence.
  * @return bool True, if in the active plugins list. False, not in the list.
  */
-function is_plugin_active( $plugin ) {
-        return in_array( $plugin, (array) get_option( 'active_plugins', array() ) ) || is_plugin_active_for_network( $plugin );
+function is_plugin_active( $plugin, $check_all=true ) {
+        if ( $check_all ) {
+                $mu_plugins = get_mu_plugins();
+                
+                if ( array_key_exists( $plugin, $mu_plugins ) ) 
+                        return true;
+                
+                $dropins = get_dropins();
+                
+                if ( array_key_exists( $plugin, $dropins ) )
+                        return true;            
+        }
+        
+        return in_array( $plugin, (array) get_option( 'active_plugins', array() ) ) || is_plugin_active_for_network( $plugin ); 
 }
 
 /**