Provide for a drillable variable structure in Twig templates

Created on 30 May 2013, almost 12 years ago

Updated 18 March 2023, about 2 years ago

Problem/Motivation

As detailed in the description for #1843798: [meta] Refactor Render API to be OO → , we currently do not have a drillable, accessible way of getting to variables that a themer may anticipate being available to a parent template. This is because variables in a sub-element may be invoked by a preprocessor that runs later.

Example from a node template:

  <!-- First image, with manual tag creation -->
  {{ hide(content.field_image.0) }}
  <img class="banner" src="{{ content.field_image.0.attrs.src }}" alt="{{ content.field_image.0.attrs.alt }}" />

  <!-- Remaining content -->
  {{ content }}

  <!-- Links -->
  {{ links }}

  <!-- Comments -->
  {{ comments }}

Before the larger, long-term goals of #1843798: [meta] Refactor Render API to be OO → are achieved, we'd like to get a stopgap for better drillability support in Drupal 8, at least for the Twig engine.

Proposed resolution

Provide a way for Twig to understand which variables need to be available to a template and adjust how they are prepared beforehand. Twig's compilation steps may offer us some insight into implementation.