Added the possibility for themes to override core module functions

doc/themes.md

@@ -59,7 +59,19 @@ The same rule applies to the JavaScript files found in
 
 they will be overwritten by files in
 
-    /view/theme/**your-theme-name**/js.
+    /view/theme/**your-theme-name**/js
+
+### Modules
+
+You have the freedom to override core modules found in
+
+    /mod
+
+They will be overwritten by files in
+
+    /view/theme/**your-theme-name**/mod
+
+Be aware that you can break things easily here if you don't know what you do. Also notice that you can override parts of the module – functions not defined in your theme module will be loaded from the core module.
 
 ## Expand an existing Theme
 
@@ -288,4 +300,4 @@ The default file is in
     /view/default.php
 
 if you want to change it, say adding a 4th column for banners of your favourite FLOSS projects, place a new default.php file in your theme directory.
-As with the theme.php file, you can use the properties of the $a variable with holds the friendica application to decide what content is displayed.
+As with the theme.php file, you can use the properties of the $a variable with holds the friendica application to decide what content is displayed.

index.php

@@ -233,7 +233,16 @@ if(strlen($a->module)) {
 	}
 
 	/**
-	 * If not, next look for a 'standard' program module in the 'mod' directory
+	 * If not, next look for module overrides by the theme
+	 */
+
+	if((! $a->module_loaded) && (file_exists("view/theme/" . current_theme() . "/mod/{$a->module}.php"))) {
+		include_once("view/theme/" . current_theme() . "/mod/{$a->module}.php");
+		// We will not set module_loaded to true to allow for partial overrides.
+	}
+
+	/**
+	 * Finally, look for a 'standard' program module in the 'mod' directory
 	 */
 
 	if((! $a->module_loaded) && (file_exists("mod/{$a->module}.php"))) {