functions.php

<?php

/**
 * Index WooCommerce Product Variations
 */

// Add product variations to the list of post types to index
function my_searchwp_indexed_post_types( $post_types ) {
	if ( ! in_array('product_variation', $post_types ) ) {
		$post_types = array_merge( $post_types, array( 'product_variation' ) );
	}
	return $post_types;
}

add_filter( 'searchwp_indexed_post_types', 'my_searchwp_indexed_post_types' );

// Update the product variations in the index when the parent product gets updated
function my_swp_purge_product_variations( $post_id, $post, $update ){

	if ( 'product' === $post->post_type ) {
		$args = array(
			'post_type'   => 'product_variation',
			'post_parent' => $post_id,
		);
		$variations = get_children( $args, ARRAY_A );

		foreach( $variations as $id => $variation ) {
			SWP()->purge_post( $id, true );
		}

		SWP()->trigger_index();
	}
}

add_action( 'save_post', 'my_swp_purge_product_variations', 10, 3 );



// OPTIONAL: Add title and custom fields support for product variations
function my_searchwp_woo_custom_post_type_args( $args, $post_type ) {
	if ( $post_type === 'product_variation' ) {
		$args['supports'] = array( 'title', 'custom-fields' );
	}

	return $args;
}

// OPTIONAL (and opt-in) to enable this functionality uncomment the next line
// add_filter( 'register_post_type_args', 'my_searchwp_woo_custom_post_type_args', 999, 2 );