Terms List block: Add Categories-specific variation (#65434)

Add two variations to the Terms List block (i.e. `core/categories` -- previously named "Categories List"): One for Categories, and another one for all other taxonomies.

This is mostly for better discoverability of what used to be the Categories List block under its new name.

Co-authored-by: ockham <bernhard-reiter@git.wordpress.org>
Co-authored-by: gziolo <gziolo@git.wordpress.org>
Co-authored-by: fabiankaegy <fabiankaegy@git.wordpress.org>

packages/block-library/src/categories/edit.js

@@ -196,7 +196,9 @@ export default function CategoriesEdit( {
 							} ) ) }
 							value={ taxonomySlug }
 							onChange={ ( selectedTaxonomy ) =>
-								setAttributes( { taxonomy: selectedTaxonomy } )
+								setAttributes( {
+									taxonomy: selectedTaxonomy,
+								} )
 							}
 						/>
 					) }

packages/block-library/src/categories/index.js

@@ -9,6 +9,7 @@ import { category as icon } from '@wordpress/icons';
 import initBlock from '../utils/init-block';
 import metadata from './block.json';
 import edit from './edit';
+import variations from './variations';
 
 const { name } = metadata;
 
@@ -18,6 +19,7 @@ export const settings = {
 	icon,
 	example: {},
 	edit,
+	variations,
 };
 
 export const init = () => initBlock( { name, metadata, settings } );

packages/block-library/src/categories/variations.js

@@ -0,0 +1,40 @@
+/**
+ * WordPress dependencies
+ */
+import { __ } from '@wordpress/i18n';
+import { category as icon } from '@wordpress/icons';
+
+const variations = [
+	{
+		name: 'terms',
+		title: __( 'Terms List' ),
+		icon,
+		attributes: {
+			// We need to set an attribute here that will be set when inserting the block.
+			// We cannot leave this empty, as that would be interpreted as the default value,
+			// which is `category` -- for which we're defining a distinct variation below,
+			// for backwards compatibility reasons.
+			// The logical fallback is thus the only other built-in and public taxonomy: Tags.
+			taxonomy: 'post_tag',
+		},
+		isActive: ( blockAttributes ) =>
+			// This variation is used for any taxonomy other than `category`.
+			blockAttributes.taxonomy !== 'category',
+	},
+	{
+		name: 'categories',
+		title: __( 'Categories List' ),
+		description: __( 'Display a list of all categories.' ),
+		icon,
+		attributes: {
+			taxonomy: 'category',
+		},
+		isActive: [ 'taxonomy' ],
+		// The following is needed to prevent "Terms List" from showing up twice in the inserter
+		// (once for the block, once for the variation). Fortunately, it does not collide with
+		// `categories` being the default value of the `taxonomy` attribute.
+		isDefault: true,
+	},
+];
+
+export default variations;