WordPress Block Editor Gutenberg running code inside ! is_admin()

Question

In my functions.php I have some code inside a function that has a if (! is_admin) condition around it. For some reason the code inside this condition is running when I edit a page in the admin. Its throwing an error which results in the page not saving.

Here is a sample of the code setup.

function conditional_payment_gateways($available_gateways){

    if (!is_admin()){

        $payment_type_ins = false;
        $payment_type_both = false;
        
        foreach (WC()->cart->get_cart() as $cart_item){
            $payment_type = $cart_item['variation']['attribute_pa_payment-type'];
            $product_type = get_post_meta($cart_item['product_id'], 'type', true );
    
            if ($payment_type == 'pay-with-insurance' && $product_type != 'Both'){
                $payment_type_ins = true;
            }
    
            if ($product_type == 'Both'){
                $payment_type_both = true;
            }
        }
    
        if($payment_type_ins){
            unset($available_gateways['authorize_net_cim_credit_card']);
        } else if ($payment_type_ins == false && $payment_type_both == false){
            unset($available_gateways['cod']);
        }
    
        return $available_gateways;
    }
}

add_filter('woocommerce_available_payment_gateways', 'conditional_payment_gateways', 10, 1);

Here is the error it causes when it runs in the editor.

PHP Fatal error:  Uncaught Error: Call to a member function get_cart()

Is there a better way to do this?

Edit: Added the full code along with the error it causing when it runs in the editor

Edit #2:

OK, So I figured out a solution for my particular problem.

Instead of using !is_admin() I can use the is_cart() & is_checkout() conditionals.

function conditional_payment_gateways($available_gateways){

    if (is_cart() || is_checkout()){

        // Code here won't fire in the admin area
        
    }
}

add_filter('woocommerce_available_payment_gateways', 'conditional_payment_gateways', 10, 1);

But, I think the larger question still remains. If is_admin() is no longer reliable in the block editor, what should we use?

As Pat J pointed out in a answer below, this is supposed to be a work around. But it didn't work for me.

Answer 1

It appears this is a known issue with the block editor (aka Gutenberg).

That Trac ticket suggests a workaround, too: replace your

if ( ! is_admin() ) { ... }

with something like this:

global $current_screen;
if ( 
    ( ! is_admin() ) && 
    ( ! 
        ( 
            // Checks the value of WP_Screen::is_block_editor().
            $current_screen instanceof \WP_Screen && 
            $current_screen->is_block_editor()
        )
    )
   ) { ... }

This code is untested. I'm pretty sure I matched the ( and ) but make sure it works as expected before you put it in production.

If you're doing this in a lot of locations (ie, > 1), I'd suggest creating a helper function even closer to the code suggested in the Trac ticket's comments:

function wpse416155_is_admin() {
    if ( is_admin() ) {
        return true;
    }
    global $current_screen;
    if ( $current_screen instanceof \WP_Screen &&
         $current_screen->is_block_editor() ) {
        return true;
    }
    return false;
}

// ...
// ...
// ...

if ( ! wpse416155_is_admin() ) {
    // ...your non-admin code here...
}