I’m using Variation Swatches plugin by AOV UP. It converts simple view of woocommerce product with variations to image swatch like you can see below. I’ve got some variations of product that are like “subvariations” and I want to make it optional. Woocommerce won’t pass this product to cart if all of them are not chosen. This is the part of plugin code:

public function get_swatch_html( $html, $args ) {
        global $woocommerce_loop;
                global $product;

        $attr = TA_WCVS()->get_tax_attribute( $args['attribute'] );
                //$attr = TA_WCVS()->$product->get_attributes();

        // Return if this is normal attribute
        if ( empty( $attr ) || ! $args['product'] instanceof WC_Product_Variable ) {
            return $html;
        }

        $options = $args['options'];
        $product = $args['product'];
        $attribute_tax_name = $args['attribute'];
        $class = "variation-selector variation-select-{$attr->attribute_type}";
        $swatches = '';
        $is_product_page = is_product();
        $defined_limit = apply_filters( 'tawcvs_swatch_limit_number', 0 );
        $out_of_stock_state = apply_filters( 'tawcvs_out_of_stock_state', '' );

        //If this product has disabled the variation swatches
        if ( $this->is_disabled_variation_swatches( $product ) ) {
            return $html;
        }

        if ( empty( $options ) && ! empty( $product ) && ! empty( $attribute_tax_name ) ) {
            $attributes = $product->get_variation_attributes();
            $options = $attributes[ $attribute_tax_name ];
        }


        if ( empty( $attr->attribute_type ) ) {
            return $html;
        }

        // Add new option for tooltip to $args variable.
        $args['tooltip'] = apply_filters( 'tawcvs_tooltip_enabled', $this->is_tooltip_enabled() );

        //Get the product variation detail for each attribute
        //If there are more than one attributes, the first one will be applied
        $collected_variations = array();

        if ( TA_WC_Variation_Swatches::is_pro_addon_active() && ! $this->is_use_attribute_image_only() ) {
            $collected_variations = TA_WC_Variation_Swatches::get_detailed_product_variations( $product, $attribute_tax_name );
        }

        if ( ! empty( $options ) && taxonomy_exists( $attribute_tax_name ) ) {
            // Get terms if this is a taxonomy - ordered. We need the names too.
            $terms = $this->get_product_variation_term( $product, $defined_limit, $attribute_tax_name, $options );

            foreach ( $terms as $term ) {

                //Check if we have the product variable for this attribute
                if ( isset( $collected_variations[ $term->slug ] ) ) {
                    $args['variation_product'] = $collected_variations[ $term->slug ];
                } else {
                    unset( $args['variation_product'] );
                }

                $swatches .= apply_filters( 'tawcvs_swatch_html', '', $term, $attr->attribute_type, $args, $product );

            }
            //If we are on shop/archived page (not product page), we will check the defined limit number of variations
            //the product still have more variations -> show the view more icon
            if ( ( ! $is_product_page || $woocommerce_loop['name'] == 'related' )
                 && 0 < $defined_limit
                 && count( $options ) > $defined_limit ) {
                $swatches .= apply_filters( 'tawcvs_swatch_show_more_html', '', $product );
            }
        }

        if ( ! empty( $swatches ) ) {
            $class .= ' hidden';
                            $swatches = '<div id="attribute_' . esc_attr( $attribute_tax_name ) . '" class="tawcvs-swatches oss-' . $out_of_stock_state . '" data-attribute_name="attribute_' . esc_attr( $attribute_tax_name ) . '">' . $swatches . '</div>';
            $html = '<div class="' . esc_attr( $class ) . '">' . $html . '</div>' . $swatches;
        }
        return $html;
    }

add_filter('tawcvs_swatch_html', function( $html, $term, $type, $args) {
    $selected = sanitize_title( $args['selected'] ) == $term->slug ? 'selected' : '';
        $name     =  apply_filters( 'woocommerce_variation_option_name', $term->name ) ;
        $tooltip  = '';

        /*if ($args['tooltip'] && $term->description) {
            $tooltip = '<span class="swatch__tooltip">' . $term->description . '</span>';
        }*/

        switch ( $type ) {
            case 'color':
                $color = get_term_meta( $term->term_id, 'color', true );
                list( $r, $g, $b ) = sscanf( $color, "#%02x%02x%02x" );
                $html = sprintf(
                    '<span class="swatch swatch-color swatch-%s %s" style="background-color:%s;color:%s;" data-value="%s">%s%s</span>',
                    esc_attr( $term->slug ),
                    $selected,
                    esc_attr( $color ),
                    "rgba($r,$g,$b,0.5)",
                    esc_attr( $term->slug ),
                    $name,
                    $tooltip
                );
                break;

            case 'image':
                $image = get_term_meta( $term->term_id, 'image', true );
                                $image = $image ? wp_get_attachment_image_src($image, 'woocommerce_single') : '';
                $image = $image ? $image[0] : WC()->plugin_url() . '/assets/images/placeholder.png';
                $label = esc_attr( $name );
                                    $html  = sprintf(
                    '<span class="swatch swatch-image swatch-%s %s" data-value="%s"><span class="swatch__tooltip">%s</span><span class="swatches_image-container"><img src="%s" alt="%s"></span>%s</span>',
                    esc_attr( $term->slug ),
                    $selected,
                    esc_attr( $term->slug ),
                                        $term->description,
                    esc_url( $image ),
                    esc_attr( $name ),
                                        $label
                                    );
                break;

            case 'label':
                $label = get_term_meta( $term->term_id, 'label', true );
                $label = $label ? $label : $name;
                $html  = sprintf(
                    '<span class="swatch swatch-label swatch-%s %s" data-value="%s">%s%s</span>',
                    esc_attr( $term->slug ),
                    $selected,
                    esc_attr( $term->slug ),
                    $label,
                    $tooltip
                );
                break;
        }

        return $html;
}, 10, 4);

it shows like this

I’ve got some code that makes attributes which are not set as visible in variations optional taken from user @Mtxz from here:

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

    if ( ! $attributes ) {
        return;
    }

    //from original script, but here we want to use it for 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 - so it can also be used with attributes of simple products (not variables)
    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>';
}
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 );
    }
}

It lists attributes of product wich are not set as variations (they are turned off to show on product page, but they’re still sticked to this product). Unfortunately they’re not parsed by WC plugin to format them to images like on screen above:
select elements

Any clues how to make it working together?