Metatag URLs

TL;DR:

Extend the Metatag module to support relative or route-based fixed URLs.

Problem with Metatag

The wonderful Metatag module allows adding arbitrary <meta> tags with arbitrary values and Token support.

Sometimes, you may want to enter a fixed URL value that is not derived from the page context (commonly in Metatag's default/"Global" tags), so Tokens don't help and you're stuck entering a relative or absolute URI.

Problem Example

Assume your custom theme provides a 60x60px Apple touch icon; it's not in public files, it's in the theme's images directory. You want to reference it across all pages of your site, so you set Metatag: Apple touch icon: 60px x 60px to "themes/custom/mytheme/images/apple60.png". This works great on the homepage of example.com, but because it's a relative URL, when you go to example.com/foo/bar, the effective URL is "example.com/foo/themes/custom/mytheme/images/apple60.png," which fails to load.

Bad solution: Know that your site's root is "/" and prefix that to your path: "/themes/custom/mytheme/images/apple60.png." This root-relative path will work, unless your root changes (on a development box, or if you move to a subdirectory install, etc.).

Good solution: Tell Metatag that the URI you're adding is relative, and have it run the URI through Url::fromUri() to output a proper URL relative to the Drupal root (whatever that is or may be in the future).

Solution provided by this module

This module adds processing for these functions in Metatag values:

• urlFromUri(...)
• urlFromRoute(...)

Simply wrap a function around your value, and the appropriate Url method will be invoked and returned. For example, "urlFromUri(base:themes/custom/mytheme/images/apple60.png)" will pass "base:themes/custom/mytheme/images/apple60.png" to Url::fromUri() and return the proper Drupal-base-relative URL.

Note: Url::fromUri() requires full URIs including the scheme. Our example uses "base:" which means relative to the Drupal root.