Twig Real Content - empty region / content check helper

Provides a "real_content" twig filter and test to determine if a certain twig variable (typically a region) has meaningful content is empty. Read the super long core issue for details.

Core issue

#953034: [meta] Themes improperly check renderable arrays when determining visibility
Once the core issue is solved (which we guess will not be soon, if ever, due to logical problems), this module may become obsolete.

TL;DR

If you need to check if a region is empty in twig, for example to not output the wrappers at all, this module is what you want, and the core issue describes the reasons why this is so complicated.

Functionality & how to use

As Twig filter:

Adds a |real_content twig filter to run on rendered variables, which filters out all wrappers and trims the code to check if there is real content.

{% set sidebar_first_rendered = page.sidebar_first|render %}
{% if sidebar_first_rendered|real_content is not empty %}
  <div class="sidebar sidebar--first">
    {{ sidebar_first_rendered }}
  </div>
{% endif %}

Without this module, it would be something like this:

{% set sidebar_first_rendered = page.sidebar_first|render %}
{% if sidebar_first_rendered|striptags('<drupal-render-placeholder><img><video><[...]>')|trim is not empty %}
  <div class="sidebar sidebar--first">
    {{ sidebar_first_rendered }}
  </div>
{% endif %}

As Twig Test:

Adds an
is real_content twig test to run on rendered variables, which filters out all wrappers and trims the code to check if there is real content. Returns TRUE if there is real content, else FALSE.

{% set sidebar_first_rendered = page.sidebar_first|render %}
{% if sidebar_first_rendered is real_content %}
  <div class="sidebar sidebar--first">
    {{ sidebar_first_rendered }}
  </div>
{% endif %}

With Twig Blocks:

Inherited Twig blocks are already rendered, so you can do:

{% extend 'paragraphs.html.twig' %}
{% block paragraph %}
  {% if parent() is real_content %}
    {{ parent() }}
  {% endif %}
{% endblock paragraph %}

Unstripped DOM elements

The following HTML elements are not being stripped, as they typically have no own DOM text content. If they are present, they are treated as existing content.

[
    '<drupal-render-placeholder>',
    '<embed>',
    '<hr>',
    '<iframe>',
    '<img>',
    '<input>',
    '<link>',
    '<object>',
    '<script>',
    '<source>',
    '<style>',
    '<svg>',
    '<video>',
];

Please create an issue, if further exclusions are required. We're also discussing to put this into config here: #3293420: Make allowed tags configurable

Render arrays and performance

As rendering a render array multiple times has negative impact on performance, we decided to disallow running this on (unrendered) render arrays directly.
Perhaps someone is interested to implement this: #3293416: Allow on render arrays and combine with isEmpty()

Related

Related modules

• Twig Capture
• Twig Tweak (also see #3268793: Add Empty Check Helpers)
• Twig Field Value

Related discussions & blog posts

• #953034: [meta] Themes improperly check renderable arrays when determining visibility
• https://drupal.stackexchange.com/questions/175389/how-do-i-properly-dete...
• https://www.drupal.org/forum/support/module-development-and-code-questio...
• https://www.previousnext.com.au/blog/right-way-check-empty-content-twig
• http://www.longlivethemonkey.com/syntaxnotes/?p=351
• https://drupal.stackexchange.com/questions/198570/verify-a-field-is-not-...

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