Limit sitename length in export filename to prevent filesystem errors (#133)

Co-authored-by: swissspidy <841956+swissspidy@users.noreply.github.com>
Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>

Author: Copilot

features/export.feature

@@ -648,6 +648,20 @@ Feature: Export content.
       000.xml
       """
 
+  Scenario: Export a site with a very long site name produces a filename within a reasonable length
+    Given a WP install
+    And I run `wp option update blogname 'This is a very long site name that exceeds fifty characters and should be truncated in the export filename'`
+
+    When I run `wp export`
+    Then STDOUT should contain:
+      """
+      thisisaverylongsitenamethatexceedsfiftycharactersa.wordpress.
+      """
+    And STDOUT should not contain:
+      """
+      thisisaverylongsitenamethatexceedsfiftycharactersandshouldbetruncated
+      """
+
   @require-wp-5.2 @require-mysql
   Scenario: Export a site and skip the comments
     Given a WP install

src/Export_Command.php

@@ -20,6 +20,11 @@
  */
 class Export_Command extends WP_CLI_Command {
 
+	/**
+	 * Maximum length of the site name component in the export filename.
+	 */
+	const MAX_FILENAME_SITENAME_LENGTH = 50;
+
 	/**
 	* Initialize the array of arguments that will be eventually be passed to export_wp.
 	*
@@ -222,6 +227,7 @@ private static function get_filename_template( $filename_format ) {
 		if ( empty( $sitename ) ) {
 			$sitename = 'site';
 		}
+		$sitename = function_exists( 'mb_substr' ) ? mb_substr( $sitename, 0, self::MAX_FILENAME_SITENAME_LENGTH ) : substr( $sitename, 0, self::MAX_FILENAME_SITENAME_LENGTH );
 		return str_replace( [ '{site}', '{date}', '{n}' ], [ $sitename, date( 'Y-m-d' ), '%03d' ], $filename_format ); // phpcs:ignore WordPress.DateTime.RestrictedFunctions.date_date
 	}