[meta] Use Twig template inheritance

added link to related issue

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I found one place where this could be useful in core: comment-wrapper.html.twig

There is an if statement in the template to see if forum module is involved. Instead, we should put a twig block in here (probably also with a documentation comment?) and Forum module should provide a twig template override that demonstrates inheritance.

This is what the comment-wrapper.html.twig file looks like currently:

<section id="comments" class="{{ attributes.class }}"{{ attributes }}>

  {# TODO forum module should extend comment template to keep the code in here clean #}
  {% if comments %}
    {% if node.type != 'forum' %}
      {{ title.prefix }}
      <h2 class="title">{{ 'Comments' | t }}</h2>
      {{ title.suffix }}
    {% endif %}

    {{ comments }}

  {% endif %}

  {% if form %}
    <h2 class="title comment-form">{{ 'Add new comment' | t }}</h2>
    {{ form }}
  {% endif %}

</section>

Here's an example of what comment-wrapper.html.twig could look like with twig template inheritance:

<section id="comments" class="{{ attributes.class }}"{{ attributes }}>

  {% if comments %}
    {% codeblock title %}
      {{ title.prefix }}
      <h2 class="title">{{ 'Comments' | t }}</h2>
      {{ title.suffix }}
    {% endcodeblock %}

    {{ comments }}

  {% endif %}

  {% if form %}
    <h2 class="title comment-form">{{ 'Add new comment' | t }}</h2>
    {{ form }}
  {% endif %}

</section>

And here's an example of the corresponding forum override, comment-wrapper--forum.html.twig:

{% extends "comment-wrapper.html.twig" %}

{% codeblock title %}
  {# code block here is empty to prevent title from showing on forums #}
{% endcodeblock %}

We may need to add a theme_hook_suggestion for a comment-wrapper--forum.html.twig in order to make this work. But it seems like this is a good use case for such a thing :)

Also, see my proposition for renaming Twig blocks to codeblocks here: #1923992: Rename 'block' to 'codeblock' in Twig for Drupal - re template inheritance :)

I'm moving this issue to the core queue so that we won't forget to add examples of template inheritance in core before d8 releases. Also converting to a meta issue so that we can track where we should be using it, so we can come back and add each instance later.

added more of why there should be no templates that are the same

sounds like we don't want to do this in core. closing.

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