Provide frontend editing experience for Layout Paragraphs.

I've created a Issue fork and made some changes to allow that the field displays the default theme templates and load a library.

1 - After update with the changes, go to /admin/config/content/layout_paragraphs/default-theme and check the checkbox option.
2 - Add your default theme library to load js and css. I created a separated styles file includind .lp-builder prepend each style so the styles will be applied on Layout Paragraphs Field only without conflicts.
Eg: mytheme/admin-library

I added the hook_theme_registry_alter to change paragraphs item and to add all your paragraphs--type templates too (if there is).
This modification search for template files inside your custom theme.

I hope it's useful and can set a path for this to be implemented.

An alternative that the module already has is to use the Layout Paragraph Builder field formatter on the 'manage display' and add or edit the paragraphs within the default theme.

Feel free to use, modify and even think it's bad :)

We're also working on improving the editorial experience here and tried out the MR in #22. It sorta worked for us, but we made a few changes:

1. In our case, we needed other templates added to the edit page, not just the Paragraph templates. For example, one of our Paragraph types displayed a list of node teasers, but those teasers were displayed using the default node template rather than the one defined in the default site theme. To solve this issue, we added a new "Additional templates to load" setting to the "Default theme" form. Any templates set there will also get added.

2. To support the new setting field above, we needed to load the theme registry for the default theme. We added a helper function to do this. Having that default theme registry array allowed us to set values like this:

$theme_registry[$template_name] = $default_theme_registry[$template_name];

This also allowed us to simplify the logic used to add Paragraph templates in the same way. Now, rather than looking at the file system to see what templates exist, we can look directly at the theme registry.

One caveat here is that we needed to call Drupal\Core\Theme\Registry directly because the default "theme.registry" service only returns data for the *active* theme. The core theme registry class called here is marked as @internal, but we could not figure out any other way to do this.

3. The MR in #22 will only add the Paragraph templates to the admin theme if you flush the cache while on the node add/edit page due to this code:

$route_name = \Drupal::routeMatch()->getRouteName();
$route_is_admin = \Drupal::service('router.admin_context')->isAdminRoute();

// Just do that if the theme is 'admin' and the page is the add or edit node form.
if($route_is_admin && ($route_name == 'entity.node.edit_form' || $route_name == 'node.add')) {

The issue is that hook_theme_registry_alter() functions are run only when the cache is flushed, not on every page load. So, for this to work, the conditional above must be removed. That will mean that the Paragraph templates are always added to the admin theme which is probably OK. That is how the MR worked in the first place when the cache was flushed from the node add/edit page, but I don't think that will cause any problems.

I've updated the branch in Git and added a patch.

One caveat here is that we needed to call Drupal\Core\Theme\Registry directly because the default "theme.registry" service only returns data for the *active* theme. The core theme registry class called here is marked as @internal, but we could not figure out any other way to do this.

Well... The signature for that class' constructor changed in Drupal 10.3! I've updated the code in the issue fork and added a new patch that will make this work with 10.3 and prior versions.

The last submitted patch, 25: 3208180-25.additional-templates.patch, failed testing. View results →
- codesniffer_fixes.patch Interdiff of automated coding standards fixes only.

Is this patch working in the direction of Layout paragraphs using the frontend CSS for the display of the Layout editing UI?
I last worked with this module in 2022 and it was my biggest gripe with it that the editing UI was completely unstyled because it did/could not call frontend CSS.
This was the one area where core Layout Builder was better than Layout Paragraphs.

Could the patch from #25 apply to 2.1.x ?