Re-add the index.php file.

lib/blocks.php

@@ -26,7 +26,6 @@ function gutenberg_reregister_core_block_types() {
 				'form-submit-button',
 				'group',
 				'html',
-				'list',
 				'list-item',
 				'missing',
 				'more',
@@ -76,6 +75,7 @@ function gutenberg_reregister_core_block_types() {
 				'heading.php'                      => 'core/heading',
 				'latest-comments.php'              => 'core/latest-comments',
 				'latest-posts.php'                 => 'core/latest-posts',
+				'list.php'                         => 'core/list',
 				'loginout.php'                     => 'core/loginout',
 				'media-text.php'                   => 'core/media-text',
 				'navigation.php'                   => 'core/navigation',

packages/block-library/src/list/index.php

@@ -0,0 +1,54 @@
+<?php
+/**
+ * Adds the wp-block-list class to the rendered list block.
+ *
+ * @package WordPress
+ */
+
+/**
+ * Adds the wp-block-list class to the rendered list block.
+ * Ensures that pre-existing list blocks use the class name on the front.
+ * For example, <ol> is transformed to <ol class="wp-block-list">.
+ *
+ * @since 6.6.0
+ *
+ * @see https://github.com/WordPress/gutenberg/issues/12420
+ *
+ * @param array  $attributes Attributes of the block being rendered.
+ * @param string $content Content of the block being rendered.
+ *
+ * @return string The content of the block being rendered.
+ */
+function block_core_list_render( $attributes, $content ) {
+	if ( ! $content ) {
+		return $content;
+	}
+
+	$processor = new WP_HTML_Tag_Processor( $content );
+
+	$list_tags = array( 'OL', 'UL' );
+	while ( $processor->next_tag() ) {
+		if ( in_array( $processor->get_tag(), $list_tags, true ) ) {
+			$processor->add_class( 'wp-block-list' );
+			break;
+		}
+	}
+
+	return $processor->get_updated_html();
+}
+
+/**
+ * Registers the `core/list` block on server.
+ *
+ * @since 6.6.0
+ */
+function register_block_core_list() {
+	register_block_type_from_metadata(
+		__DIR__ . '/list',
+		array(
+			'render_callback' => 'block_core_list_render',
+		)
+	);
+}
+
+add_action( 'init', 'register_block_core_list' );