Woocommerce: use non-variation attributes from frontend - allow customers to select term (option) from non-variation attributes on variable or simple products frontend pages, add selection to cart item, display it in cart, add it to order item

wp-woocommerce-allow-non-variation-attributes-frontend-selection.php

<?php
/**
 * Inspired from: https://gist.github.com/dazecoop/548b2621e86fb030da8e5adb1bfe484f
 * 
 * How to use:
 * - add to your function.php or related
 *
 * What you can use it for:
 * Variable products:
 * - you have variable product with some attributes not used for variations
 * - you still want to let your users choose some of those attributes values on frontend
 * - eg: your have an attribute that don't impact prices, and that is required or not, and don't want to create useless variations for those attributes
 *
 * Simple product:
 * - you have a single product, and want to allow user to select some of its attributes values from frontend
 */

/**
 * List available attributes on product page in a drop-down selection
 */
function list_attributes_on_product_page() {
    global $product;
    $attributes = $product->get_attributes();

    if ( ! $attributes ) {
        return;
    }

    //uncomment this if you only want fields to be displayed for non-variable products
    /*if ($product->is_type( 'variable' )) {
        return;
    }*/

    echo '<div style="padding-bottom:15px;">';

    foreach ( $attributes as $attribute ) {

        //If product is variable, and attribute is used for variation: woocommerce already handle this input
        if($product->is_type( 'variable' ) && $attribute['variation']) {
            continue;
        }

        //get taxonomy for the attribute - eg: Size
        $taxonomy = get_taxonomy($attribute['name']);

        //get terms - eg: small
        $options = wc_get_product_terms( $product->get_id(), $attribute['name'], array( 'fields' => 'all' ) );
        $label = str_replace('Product ', '', $taxonomy->label);
        //display select input
        ?>
        <div style="padding-bottom:8px;">
            <label for="attribute[<?php echo $attribute['id']; ?>]"><?php echo $label; ?></label>
            <br />
            <!-- add required attribute or not, handle default with "selected" attribute depending your needs -->
            <select name="attribute[<?php echo $attribute['id']; ?>]" id="attribute[<?php echo $attribute['id']; ?>]">
                <option value disabled selected>Choose an option</option>
                <?php foreach ( $options as $pa ): ?>
                    <option value="<?php echo $pa->name; ?>"><?php echo $pa->name; ?></option>
                <?php endforeach; ?>
            </select>
        </div>
        <?php
    }

    echo '</div>';
}
//update the "woocommerce_before_add_to_cart_button" to change the position of the HTML output
add_action('woocommerce_before_add_to_cart_button', 'list_attributes_on_product_page');

/**
 * Add selected attributes to cart items
 */
add_filter('woocommerce_add_cart_item_data', 'add_attributes_to_cart_item', 10, 3 );
function add_attributes_to_cart_item( $cart_item_data, $product_id, $variation_id ) {
    $attributes = $_POST['attribute'] ?? null;

    if (empty( $attributes ) ) {
        return $cart_item_data;
    }

    $cart_item_data['attributes'] = serialize($attributes);

    return $cart_item_data;
}

/**
 * Display attributes in cart
 */
add_filter( 'woocommerce_get_item_data', 'display_attributes_in_cart', 10, 2 );
function display_attributes_in_cart( $item_data, $cart_item ) {
    if ( empty( $cart_item['attributes'] ) ) {
        return $item_data;
    }

    foreach (unserialize($cart_item['attributes']) as $attributeID => $value) {
        $attribute = wc_get_attribute($attributeID);
        $item_data[] = array(
            'key'     => $attribute->name,
            'value'   => $value,
            'display' => '',
        );
    }

    return $item_data;
}

/**
 * Add attribute data to order items
 */
add_action( 'woocommerce_checkout_create_order_line_item', 'add_attributes_to_order_items', 10, 4 );
function add_attributes_to_order_items( $item, $cart_item_key, $values, $order ) {
    if ( empty( $values['attributes'] ) ) {
        return;
    }

    foreach (unserialize($values['attributes']) as $attributeID => $value) {
        $attribute = wc_get_attribute($attributeID);
        $item->add_meta_data( $attribute->name, $value );
    }
}

Hi I've been trying using your code on product variations but somehow it didn't work on woo 8.5.2
The following code modifications work without using wc_get_attribute()

//attributes dropdown without variation
function list_attributes_on_product_page() {
    global $product;
    $attributes = $product->get_attributes();
    //uncomment this if you only want fields to be displayed for non-variable products
    if ($product->is_type( "variable" ) && isset($attributes)) {

        echo "<div style="padding-bottom:15px;">";

        foreach ( $attributes as $id=>$attribute ) {

            //If product is variable, and attribute is used for variation: woocommerce already handle this input
            if($product->is_type( "variable" ) && $attribute["variation"]) {
                continue;
            }

            //get terms - eg: small
            $attribute_options = $attribute->get_options();  
            $label = $attribute->get_name();
            $attribute_name = urlencode($label);
            //display select input
            ?>
            <div style="padding-bottom:8px;">
                <label for="<?php echo $id; ?>"><?php echo $label; ?></label>
                <br />
                <!-- add required attribute or not, handle default with "selected" attribute depending your needs -->
                <select name="attribute[<?php echo $id; ?>]" id="attribute[<?php echo $id; ?>]">
                    <option value disabled selected>Choose an option</option>
                    <?php foreach ( $attribute_options as $key => $attribute_option ): ?>
                        <option value="<?php echo $attribute_option; ?>"><?php echo $attribute_option; ?></option>
                    <?php endforeach; ?>
                </select>
            </div>
            <?php
        }

        echo "</div>";

    }
}
//update the "woocommerce_before_add_to_cart_button" to change the position of the HTML output
add_action("woocommerce_before_add_to_cart_button", "list_attributes_on_product_page");



/**
 * Add selected attributes to cart items
 */
add_filter("woocommerce_add_cart_item_data", "add_attributes_to_cart_item", 10, 3 );
function add_attributes_to_cart_item( $cart_item_data, $product_id, $variation_id ) {
    $attributes = $_POST["attribute"] ?? null;

    if (empty( $attributes ) ) {
        return $cart_item_data;
    }

    $cart_item_data["attributes"] = serialize($attributes);

    return $cart_item_data;
}


/**
 * Display attributes in cart
 */
add_filter( "woocommerce_get_item_data", "display_attributes_in_cart", 10, 2 );
function display_attributes_in_cart( $item_data, $cart_item ) {
    if ( empty( $cart_item["attributes"] ) ) {
        return $item_data;
    }

    foreach (unserialize($cart_item["attributes"]) as $name => $value) {
        $item_data[] = array(
            "key"     => $name,
            "value"   => $value,
            "display" => "",
        );
    }

    return $item_data;
}

/**
 * Add attribute data to order items
 */
add_action( "woocommerce_checkout_create_order_line_item", "add_attributes_to_order_items", 10, 4 );
function add_attributes_to_order_items( $item, $cart_item_key, $values, $order ) {
    if ( empty( $values["attributes"] ) ) {
        return;
    }

    foreach (unserialize($values["attributes"]) as $name => $value) {
        $item->update_meta_data( $name, $value );
    }
}