Filter callout block render and render a notice block

Closes WordPress/wordpress.org#374

mu-plugins/blocks/notice/index.php

@@ -9,6 +9,8 @@
 // Run after `WPorg_Handbook_Callout_Boxes` registers the shortcodes.
 add_action( 'init', __NAMESPACE__ . '\init', 11 );
 
+add_filter( 'pre_render_block', __NAMESPACE__ . '\render_callout_block_as_notice', 11, 2 );
+
 /**
  * Registers the block using the metadata loaded from the `block.json` file.
  * Behind the scenes, it registers also all assets so they can be enqueued
@@ -70,3 +72,28 @@ function render_shortcode( $attr, $content, $tag ) {
 
 	return $final_markup;
 }
+
+/**
+ * Renders a callout block as a notice.
+ *
+ * @param string|null $pre_render The pre-rendered content or null.
+ * @param array       $parsed_block The parsed block array.
+ * @return string|null The rendered notice or the original pre-render value.
+ */
+function render_callout_block_as_notice( $pre_render, $parsed_block ) {
+	if ( is_admin() || 'wporg/callout' !== $parsed_block['blockName'] ) {
+		return $pre_render;
+	}
+
+	$callout_wrapper = $parsed_block['innerHTML'];
+	// Extract the specific "callout-*" class and remove the "callout-" prefix
+	preg_match( '/\bcallout-([\w-]+)\b/', $callout_wrapper, $matches );
+	$tag = $matches[1] ?? 'info';
+
+	$content = '';
+	foreach ( $parsed_block['innerBlocks'] as $inner_block ) {
+		$content .= render_block( $inner_block );
+	}
+
+	return render_shortcode( null, $content, $tag );
+}