I want to apply following 2 case :
To avoid your site to be off,
global $woocommerce;is missing.
Nowglobal $woocommerce;with$woocommerce->cartis now simply replaced byWC()->cart.To check if cart is empty, you should use WC()->cart->is_empty(), as is_empty() is a conditional method of WC_cart class.
After, on checkout page (in both cases) if user is not logged in, you want to redirect him to my_account page (login/create account area).
Now on my_account page, when a logged user has something in his cart, you want to redirect him on checkout page.
Here is the code you need:
add_action('template_redirect', 'woocommerce_custom_redirections');
function woocommerce_custom_redirections() {
// Case1: Non logged user on checkout page (cart empty or not empty)
if ( !is_user_logged_in() && is_checkout() )
wp_redirect( get_permalink( get_option('woocommerce_myaccount_page_id') ) );
// Case2: Logged user on my account page with something in cart
if( is_user_logged_in() && ! WC()->cart->is_empty() && is_account_page() )
wp_redirect( get_permalink( get_option('woocommerce_checkout_page_id') ) );
}
Code goes in function.php file of your active child theme. Tested and works.
Reference (Woocommerce documentation):