Component library missing when rendered via Drupal.theme (via JS not via Twig)

The scenario which leads me to this issue was the following: How to use a SDC to theme Drupal messages individually?

Since Drupal 10.3 and this bug in particular 🐛 10.3 upgrade now missing status-message theme sugestions Active , there is no way for individual message to use a Twig template. Each Drupal messages are rendered via Drupal.theme.message.

Consequently there is no other choice than implementing a custom Drupal.theme.message method in a custom theme or a custom module and - if one wants to use a SDC to render messages - I don't see any other way than to pass the component output to drupalSettings to be reused in JS.

Example code in this snippet: https://git.drupalcode.org/-/snippets/214

Each Drupal messages are rendered via Drupal.theme.message.

So, maybe we need to fix the root cause instead of introducing a workaround: 🐛 10.3 upgrade now missing status-message theme sugestions Active

This is "the root cause" for this specific scenario (e.g. using SDC to theme Messages).

The feature request is still relevant for any other use cases such as printing mycomponent:xyz using a custom Drupal.theme.xyz in JS

So, we need to add attach the asset library from ComponentElement render element in preRenderComponent() method?

The asset library is already attached in ComponentNodeVisitor:

    $print_nodes[] = new PrintNode(new FunctionExpression(
      new TwigFunction('attach_library', [$env->getExtension(TwigExtension::class), 'attachLibrary']),
      new Node([new ConstantExpression($component->getLibraryName(), $line)]),
      $line
    ), $line);

It would be the dream to remove ComponentNodeVisitor and move all the logic to ComponentElement but it is not possible yet because it will be a compatibility break for the poor souls using Twig include or embed to call a component template.

So, if we add asset library attachment in ComponentElement, the library will be attached twice. It is supposed to be OK because the asset library API takes care of this, but we need to be sure there is no side effects.

Changes are made on on 11.x (our main development branch) first, and are then back ported as needed according to our policies.