Twig templates in a parent theme extending a generic template will extend instead the overriding template from a child theme
I don’t even know what’s a bug or a feature anymore, when it comes to Drupal 8 subthemes interacting with parent themes.
I’m pretty sure this falls into the category of a feature that was expected to be broken, but turns out to be working.
Twig templates in a parent theme extending a generic template will extend instead the template from a child theme if the child theme overrides that generic template (using generic to mean the parent theme didn’t specify a namespace).
The Bulma theme has a field–text-long.html.twig template which doesn’t do anything but refer to (extends without changes) a field–text.html.twig template which, in turn, doesn’t do anything but add a content class to attributes and defers to the field template:
{% extends "field.html.twig" %}
I’m overriding field.html.twig in our subtheme of Bulma (actually, a sub-sub-theme, with Octavia)
So i guess because it doesn’t specify @bulma in itself, it’s overriding whichever field.html.twig gets used, which would be the one in the child-most theme. So cool, i guess, just unexpected given all i’ve read about extends not working ideally with theme inheritance, namely:
{% extends “foo.html.twig” %} in Twig templates does not respect theme inheritance https://www.drupal.org/project/drupal/issues/2387069