Fix #718 - change method of updating theme paths

[swalkinshaw]

After a deploy we were running switch_theme would had the side effect of sometimes making sidebar widgets inactive.

This uses a simpler, more direct method of updating stylesheet_root and template_root which should be less error-prone since it does less.

[coreyworrell]

The reason menus and sidebar widgets become inactive is because of the two functions registered in wp-includes/default-filters.php

add_action( 'after_switch_theme', '_wp_menus_changed' );
add_action( 'after_switch_theme', '_wp_sidebars_changed' );

I still have no idea why the issue only happens occasionally, but it appears that you can bypass those by pretending the theme switch came from the Customizer:

wp-includes/theme.php [check_theme_switched()] (this is bound to init action, so it would only happen on first page load after the deployment)

if ( get_option( 'theme_switched_via_customizer' ) ) {
	remove_action( 'after_switch_theme', '_wp_menus_changed' );
	remove_action( 'after_switch_theme', '_wp_sidebars_changed' );
	update_option( 'theme_switched_via_customizer', false );
}

The new method you have here should probably work fine too, but if you didn't want to hard code a path in there then the following should work:

wp eval 'wp_clean_themes_cache(); update_option("theme_switched_via_customizer", true); switch_theme(get_stylesheet());'