skip rendering nested navigation blocks

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

@@ -410,6 +410,24 @@ function( $block ) {
 	return array_values( $filtered );
 }
 
+/**
+ * Bail on rendering nested navigation blocks
+ *
+ * @param array $parsed_blocks the parsed blocks to be normalized.
+ * @return array the normalized parsed blocks.
+ */
+function block_core_navigation_has_nested_core_navigation( $parsed_blocks ) {
+	$filtered = array_filter(
+		$parsed_blocks,
+		function( $block ) {
+			return $block['blockName'] === 'core/navigation';
+		}
+	);
+
+	// Reset keys.
+	return count( $filtered ) > 0;
+}
+
 /**
  * Retrieves the appropriate fallback to be used on the front of the
  * site when there is no menu assigned to the Nav block.
@@ -443,13 +461,18 @@ function block_core_navigation_get_fallback_blocks() {
 
 	// Use the first non-empty Navigation as fallback if available.
 	if ( $navigation_post ) {
-		$maybe_fallback = block_core_navigation_filter_out_empty_blocks( parse_blocks( $navigation_post->post_content ) );
+		$parsed_blocks = parse_blocks( $navigation_post->post_content );
+		$maybe_fallback = block_core_navigation_filter_out_empty_blocks( $parsed_blocks );
 
 		// Normalizing blocks may result in an empty array of blocks if they were all `null` blocks.
 		// In this case default to the (Page List) fallback.
 		$fallback_blocks = ! empty( $maybe_fallback ) ? $maybe_fallback : $fallback_blocks;
 	}
 
+	if ( block_core_navigation_has_nested_core_navigation( $parsed_blocks ) ) {
+		return [];
+	}
+
 	/**
 	 * Filters the fallback experience for the Navigation block.
 	 *
@@ -511,7 +534,6 @@ function block_core_navigation_from_block_get_post_ids( $block ) {
 function render_block_core_navigation( $attributes, $content, $block ) {
 
 	static $seen_menu_names = array();
-	static $seen_ref        = array();
 
 	// Flag used to indicate whether the rendered output is considered to be
 	// a fallback (i.e. the block has no menu associated with it).
@@ -582,11 +604,6 @@ function render_block_core_navigation( $attributes, $content, $block ) {
 
 	// Load inner blocks from the navigation post.
 	if ( array_key_exists( 'ref', $attributes ) ) {
-		if ( in_array( $attributes['ref'], $seen_ref, true ) ) {
-			return '';
-		}
-		$seen_ref[] = $attributes['ref'];
-
 		$navigation_post = get_post( $attributes['ref'] );
 		if ( ! isset( $navigation_post ) ) {
 			return '';