Shopify canonicalize product into first collection

product-thumbnail.liquid

...
  {% if product.collections[0].handle.size > 0 %}
    {% assign canonical_url = shop.url | append: '/collections/' | append: product.collections[0].handle | append: '/products/' | append: product.handle %}
  {% else  %}
    {% assign canonical_url = product.url | within: collection %}
  {% endif %}
...

product.liquid

<script>
  // Force canonicalization into product.collections[0]
  // Nasty workaround for forcibly redirecting old /products/ links
  jQuery(document).ready(function($){
    var current_url = document.URL,
        canonical_url_stub = $('#canonicalHref').attr('href'),
        returnUrl;
    if (!canonical_url_stub) {
      // console.log('no stub!');
      return;
    } else if (current_url.includes('/collections')) {
      // console.log('already in collection:', current_url, canonical_url_stub);
      return;
    } else {
      // console.log('reroute:', current_url, canonical_url_stub);
      window.location = `${current_url.split('/products')[0]}${canonical_url_stub}` ;
      return;
    }
  });
</script>