Introduce a way to distinguish between different types of layouts

In the contrib module we are adding a plugin system (#2828506: Introduce a plugin system for paragraphs types) which add fields to a paragraph when editing.

We want to split the fields to appear in two tabs (js based approach) but the user should be able to set a specific region of each field (content and plugin fields).

For doing so we tried the module added in: #2796173: Add experimental Field Layout module to allow entity view/form modes to switch between layouts and we were able to add two regions "Content" and "Behavior" to the paragraph entity form display.

The problem is that the plugin that we added is being shown in every entity form display and might be good if the layout plugins can check the entity type so we can add our layout plugin to be selected just in the paragraphs entities.

+++ b/core/lib/Drupal/Core/Layout/LayoutDefinition.php
@@ -267,6 +276,27 @@ public function setDescription($description) {
+   * Returns the types this layout is suitable for.
+   *
+   * @return string[]
+   *   An array of type strings, see
+   *   \Drupal\Core\Layout\Annotation\Layout::$types for common types.
+   */
+  public function getTypes() {
+    return $this->types;
+  }

what about a hasType() method?

Re paragraphs, yes and no. It would allow us to do that with a custom layout system (although it wouldn't automatically exclude our layout type from other usages unless they limit by a specific type as well).

But that's not what we'd do, we would provide a layout for field_layout. As mentioned in IRC, we actually don't even really need a layout system... all we really care about is having two regions in the UI and were hoping to somehow rely on field_layout to help us with that.

A quick idea that I had is to add an alter hook to the provided layouts in field_layout.module that also accepts the entity type and possible more context. Then we could alter it so that paragraphs form display only gets that single layout and we'd unset it for every other entity type. That might or might not rely on this types concept.

+1 for this direction.

To clarify the use case, it is focused around being able to indicate that e.g. certain layouts are designed for full page displays (think: Panels Everywhere) whereas others would work better for e.g. an entity display (think: Panels or Panelizer) or even a block display (think: Mini Panels).

This option feels like a solution looking for a problem.

I think we should close this as "won't fix", wait to see what #2848549: Refine the layout selection UI comes up with and drive all changes from that.