title: WooCommerce: filter products by attribute and hide product if variation is out of stock
body: <p>I use the built in WooCommerce filter by attribute widget which works for what I need, but my issue is, that if I filter on a size, I get all products with that size as an attribute, also when they are out of stock...</p>
  <p>My products are created as a variable product with variations on size and color</p>
  <p>What I want, is to filter a size and only display products in that size that is in stock.</p>