This function had been marked as deprecated since 3.4.0. Use wp_get_themes()

Get the allowed themes for the current blog.

Signature

get_allowed_themes()

Return

(array) $themes Array of allowed themes.

Source

function get_allowed_themes() {
	_deprecated_function( __FUNCTION__, '3.4', "wp_get_themes( array( 'allowed' => true ) )" );

	$themes = wp_get_themes( array( 'allowed' => true ) );

	$wp_themes = array();
	foreach ( $themes as $theme ) {
		$wp_themes[ $theme->get('Name') ] = $theme;
	}

	return $wp_themes;
}
WP Trac GitHub

Link here