No /themes/ folder causes strange behaviour

[slaFFik]

I know, that it's a tricky behaviour, but the problem exists.

1. Unzip WordPress files to appropriate place
2. Go to /wp-content/ and delete /themes/ folder
3. Install WordPress using it's wizard (ignore error in Dashboard that no theme activated)
4. Go to Plugins page in admin area
5. Install BuddyPress (this plugin register the theme BP Default that is situated in plugin folder - this is very important)
6. Activate BuddyPress and complete its wizard to make BP functional
7. Go to Themes page in wp-admin
8. You will now see BP Default Theme. Try to activate it
9. Ta-da! You've just unlocked a new badge for catching an error.

[SergeyBiryukov]

Got "Cheatin' uh?" message from wp-admin/themes.php:
​http://core.trac.wordpress.org/browser/tags/3.5.1/wp-admin/themes.php#L20

BuddyPress Default theme is correctly registered with /plugins/buddypress/bp-themes as theme root, however wp_get_theme( 'bp-default' ) later looks for WP_CONTENT_DIR . '/themes' instead.

Caused by the early return in get_theme_roots() and get_raw_theme_root():
​http://core.trac.wordpress.org/browser/tags/3.5.1/wp-includes/theme.php#L285
​http://core.trac.wordpress.org/browser/tags/3.5.1/wp-includes/theme.php#L510

if ( count($wp_theme_directories) <= 1 )
	return '/themes';

Commenting out these lines in both functions allowed me to activate BuddyPress Default theme.

Introduced in [15641], corrected in [16424]. It assumes that if there's only one theme directory, it's wp-content/themes. According to the ticket description, this assumption isn't always correct, although it's probably an edge case.

Reproduced in 3.1 as well. There was no "Cheatin' uh?" message (it was introduced later in [21010]), however validate_current_theme() still failed, and the theme could not be activated:
​http://core.trac.wordpress.org/browser/tags/3.1/wp-admin/themes.php#L60

[nacin]

Duplicate of #11282, I think.

[SergeyBiryukov]

Related, but not exactly a duplicate.

[SergeyBiryukov]

#28263 was marked as a duplicate.