Auto-select "Primary Menu " when switching themes

[azaozz]

Now that we have auto-matching of sidebars when switching themes, it's time to do the same for at least the Primary Menu. This would improve the UX quite a bit.

While testing the widgets/sidebars had to switch themes many times and since my test install has few hundred pages, each time I've ended up with a huge menu on the front end. That of course looks completely broken.

Further to keeping the setting for Primary Menu on theme switching IMHO we should auto-set it as soon as a menu is created. This would fix the most unfriendly experience with the menus screen.

I'm in. Looking like this will need to be 3.4, though, since there's no patch and today is freeze?

Yes, it can use the same method as the sidebars transfer from the old theme to the new.

This is not a full solution for this problem but if you looking for a temporary solution for similar theme switches that have same theme locations (child themes etc):

​http://wordpress.stackexchange.com/questions/58164/assign-menus-to-theme-locations-with-theme-activation

/* 
 This action copies old theme's theme location saves to 
 new theme if new theme doesnt have saves before.
 */
 add_action( 'after_switch_theme',  'ajx_theme_locations_rescue' );
 function ajx_theme_locations_rescue() {
	// bug report / support: http://www.unsalkorkmaz.com/
	// We got old theme's slug name
	$old_theme = get_option( 'theme_switched' );
	// Getting old theme's settings
	$old_theme_mods = get_option("theme_mods_{$old_theme}");
	// Getting old theme's theme location settings
	$old_theme_navs = $old_theme_mods['nav_menu_locations'];
	// Getting new theme's theme location settings
	$new_theme_navs = get_theme_mod( 'nav_menu_locations' );
	
	// If new theme's theme location is empty (its not empty if theme was activated and set some theme locations before)
	if (!$new_theme_navs) {
		// Getting registered theme locations on new theme
		$new_theme_locations = get_registered_nav_menus();

		foreach ($new_theme_locations as $location => $description ) {
			// We setting same nav menus for each theme location 
			$new_theme_navs[$location] = $old_theme_navs[$location];
		}
		
		set_theme_mod( 'nav_menu_locations', $new_theme_navs );
		
	}
 }