bartik_links__system_main_menu() doesn't work

Question

When I implement bartik_links__system_main_menu($variables) in my template.php file, there is nothing different in the main menu than the previous one. I've changed some of the markup in this function; I checked it in the theme developer, and the function that is responsible for the main menu is still theme_links() rather than bartik_links__system_main_menu($variables).

Why?

Answer 1

Make sure that:

1. theme('links__system_main_menu', ... is actually used to output the menu.
2. There are no issues with your code.
3. Caches have been cleared after adding the function (admin/config/development/performance).

To better understand what system_main_menu is all about check keithm's answer here. The main part of the explanation is this:

links__system_main_menu is a theme hook pattern of the form [base hook]__[context]. When links are themed with theme('links__system_main_menu', $vars), theme() will search for and use theme_links__system_main_menu() if it has been defined. If not, it will use theme_links().

Official documentation about it can be found here.