Updated: Comment #N
Problem/Motivation
Twig has this concept of template include and extends. Currently we have to specify the complete path to a template file to include it. This fact, makes this feature of twig unusable for contrib module and themes.
Proposed resolution
Add a twig namespace for each module and theme (somewhere in CoreServiceProvider::registerTwig).
Syntax in templates without namespaces.
{% extends "core/themes/bartik/templates/node.html.twig" %}Syntax in templates namespaces.
{% extends "@bartik/node.html.twig" %}Remaining tasks
Implementations, Tests, Docs
User interface changes
None.
API changes
None. We do not use include or extends in our templates atm.