System Menu blocks do not have attributes

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For the specific test coverage still needed.

Also I see that the tests were updated is that because this attribute is now required? Won't this break existing sites that don't have it?

Opened an MR with a slightly different approach.

The existing patch will add an ID to every since block that is added via LB, which feels a bit overkill to solve this. Instead I've added a default ID that will be applied to system_menu_blocks if one does not exist. If people like this approach I'll add some tests

The Needs Review Queue Bot → tested this issue.

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Seems a few other block--system-menu-block.html.twig in core. Is there a place we can add an assertion to?

This appears no longer to be an issue as of 11.3.x. Placing a menu block on the page successfully generates unique ID attributes; placing a second instance of the same menu block confirms that the ID attributes and corresponding aria-labelledby attributes are unique. I haven't tracked down the core commit responsible for this yet, but will set this to "Postponed" given the above.

Example markup of first instance of menu block:

<nav id="block-olivero-mainnavigation" class="contextual-region primary-nav block block-menu navigation menu--main" aria-labelledby="block-olivero-mainnavigation-menu" role="navigation">
      
  <h2 class="block__title" id="block-olivero-mainnavigation-menu">Main navigation</h2>

Example markup of second instance of menu block:

<nav id="block-olivero-mainnavigation-2" class="contextual-region primary-nav block block-menu navigation menu--main" aria-labelledby="block-olivero-mainnavigation-2-menu" role="navigation">
      
  <h2 class="block__title" id="block-olivero-mainnavigation-2-menu">Main navigation</h2>

My previous comment was wrong. This is still an issue in Drupal core, though it only manifests in the context of placing a menu block using Layout Builder.

Seems a few other block--system-menu-block.html.twig in core. Is there a place we can add an assertion to?

Agreed that modifying the Twig templates is not the best approach here. Instead, we can supply the ID attribute to all templates through the SystemMenuBlock::build() method. The rendering logic for a unique ID can be modeled exactly on block/src/Hook/BlockHooks::preprocessBlock(), per below:

    // Create a valid HTML ID and make sure it is unique.
    if (!empty($variables['elements']['#id'])) {
      $variables['attributes']['id'] = Html::getUniqueId('block-' . $variables['elements']['#id']);
    }

I've created an alternate merge request, at https://git.drupalcode.org/project/drupal/-/merge_requests/12664