WP_Navigation_Block_Renderer::get_markup_for_inner_block() can return null causing PHP8 error

[afragen]

class-wp-html-tag-processor.php on line 876 can have an null value passed to strlen() as $this->html resulting in a PHP8 error.

This seems to have originated from a change in ​https://github.com/WordPress/wordpress-develop/commit/1f8bb9fb333f5a5fb955d1a2298a00b6443eacc8#diff-1bea3165bce53d53ac51db1b623291fcd75ca59e08ec124df652312329160685L143-R169 where static::get_markup_for_inner_block( $inner_block ) can return null instead of an empty string.

If the function is changed from

private static function get_markup_for_inner_block( $inner_block ) {
	$inner_block_content = $inner_block->render();
	if ( ! empty( $inner_block_content ) ) {
		if ( static::does_block_need_a_list_item_wrapper( $inner_block ) ) {
			return '<li class="wp-block-navigation-item">' . $inner_block_content . '</li>';
		}
		return $inner_block_content;
	}
}

to the following, this is mitigated.

private static function get_markup_for_inner_block( $inner_block ) {
	$inner_block_content = $inner_block->render();
	if ( ! empty( $inner_block_content ) ) {
		if ( static::does_block_need_a_list_item_wrapper( $inner_block ) ) {
			return '<li class="wp-block-navigation-item">' . $inner_block_content . '</li>';
		}
	} else {
		$inner_block_content = '';
	}

	return $inner_block_content;
}

[afragen]

Probably a better fix.

	private static function get_markup_for_inner_block( $inner_block ) {
		$inner_block_content = $inner_block->render();
		if ( ! empty( $inner_block_content ) ) {
			if ( static::does_block_need_a_list_item_wrapper( $inner_block ) ) {
				return '<li class="wp-block-navigation-item">' . $inner_block_content . '</li>';
			}
		}
		return $inner_block_content;
	}

[get_dave]

Thanks for catching this and reporting.

I went ahead and raised and Issue in the Gutenberg repo as all blocks are maintained there:

​https://github.com/WordPress/gutenberg/issues/59814

[swissspidy]

There's a PR in progress on the Gutenberg repo, so adding has-patch

[swissspidy]

Now that your upstream PR is merged and ​https://github.com/WordPress/gutenberg/issues/59814 is closed, the fix will be automatically included in the next package update for WP 6.5 RC3 (see #60315). Therefore closing as reported-upstream since no further action is required here.