Automatically link to WooCommerce Product Variation detail when searching for a Product Variation SKU

functions.php

<?php

function my_maybe_woocommerce_variation_permalink( $permalink ) {
  if ( ! is_search() ) {
    return $permalink;
  }

  // check to see if the search was for a product variation SKU
  $sku = get_search_query();
  $args = array(
    'post_type'       => 'product_variation',
    'posts_per_page'  => 1,
    'fields'          => 'ids',
    'meta_query'      => array(
      array(
        'key'     => '_sku',
        'value'   => $sku,
      ),
    ),
  );
  $variation = get_posts( $args );

  // make sure the permalink we're filtering is for the parent product
  if ( get_permalink( wp_get_post_parent_id( $variation[0] ) ) !== $permalink ) {
    return $permalink;
  }

  if ( ! empty( $variation ) && function_exists( 'wc_get_attribute_taxonomy_names' ) ) {

    // this is a variation SKU, we need to prepopulate the filters
    $variation_id = absint( $variation[0] );
    $variation_obj = new WC_Product_Variation( $variation_id );
    $attributes = $variation_obj->get_variation_attributes();

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

    $permalink = add_query_arg( $attributes, $permalink );
  }

  return esc_url( $permalink );
}

add_filter( 'the_permalink', 'my_maybe_woocommerce_variation_permalink' );