Today I needed to migrate a URL/Link into a Drupal 8 site, and I was scratching my head over how to migrate it so there were distinct values for the URL (the actual link) and the Label (the 'title' that displays to end users and is clickable). Drupal 8's Link field type allows you to set a URL in addition to an optional (or required) label, but by default, if you just migrate the URL, the label will be blank.
I first set up the migration config like so:
source_url was defined in the migration's
In my case, the source data didn't have a label, but I wanted to set a default label so the Drupal 8 site could display that as the clickable link (instead of an ugly long URL). To do that, it's similar to migrating a formatted text field, where you can migrate individual components of the field using the syntax
[field_name]/[component]. In a Link field's case, it looks like: