Core_Upgrader::upgrade( object $current, array $args = array() ): string|false|WP_Error

66	public function upgrade( $current, $args = array() ) {67		global $wp_filesystem;68 69		require ABSPATH . WPINC . '/version.php'; // $wp_version;70 71		$start_time = time();72 73		$defaults    = array(74			'pre_check_md5'                => true,75			'attempt_rollback'             => false,76			'do_rollback'                  => false,77			'allow_relaxed_file_ownership' => false,78		);79		$parsed_args = wp_parse_args( $args, $defaults );80 81		$this->init();82		$this->upgrade_strings();83 84		// Is an update available?85		if ( ! isset( $current->response ) || 'latest' === $current->response ) {86			return new WP_Error( 'up_to_date', $this->strings['up_to_date'] );87		}88 89		$res = $this->fs_connect( array( ABSPATH, WP_CONTENT_DIR ), $parsed_args['allow_relaxed_file_ownership'] );90		if ( ! $res || is_wp_error( $res ) ) {91			return $res;92		}93 94		$wp_dir = trailingslashit( $wp_filesystem->abspath() );95 96		$partial = true;97		if ( $parsed_args['do_rollback'] ) {98			$partial = false;99		} elseif ( $parsed_args['pre_check_md5'] && ! $this->check_files() ) {100			$partial = false;101		}102 103		/*104		 * If partial update is returned from the API, use that, unless we're doing105		 * a reinstallation. If we cross the new_bundled version number, then use106		 * the new_bundled zip. Don't though if the constant is set to skip bundled items.107		 * If the API returns a no_content zip, go with it. Finally, default to the full zip.108		 */109		if ( $parsed_args['do_rollback'] && $current->packages->rollback ) {110			$to_download = 'rollback';111		} elseif ( $current->packages->partial && 'reinstall' !== $current->response && $wp_version === $current->partial_version && $partial ) {112			$to_download = 'partial';113		} elseif ( $current->packages->new_bundled && version_compare( $wp_version, $current->new_bundled, '<' )114			&& ( ! defined( 'CORE_UPGRADE_SKIP_NEW_BUNDLED' ) || ! CORE_UPGRADE_SKIP_NEW_BUNDLED ) ) {115			$to_download = 'new_bundled';116		} elseif ( $current->packages->no_content ) {117			$to_download = 'no_content';118		} else {119			$to_download = 'full';120		}121 122		// Lock to prevent multiple Core Updates occurring.123		$lock = WP_Upgrader::create_lock( 'core_updater', 15 * MINUTE_IN_SECONDS );124		if ( ! $lock ) {125			return new WP_Error( 'locked', $this->strings['locked'] );126		}127 128		$download = $this->download_package( $current->packages->$to_download, false );129 130		/*131		 * Allow for signature soft-fail.132		 * WARNING: This may be removed in the future.133		 */134		if ( is_wp_error( $download ) && $download->get_error_data( 'softfail-filename' ) ) {135			// Output the failure error as a normal feedback, and not as an error:136			/** This filter is documented in wp-admin/includes/update-core.php */137			apply_filters( 'update_feedback', $download->get_error_message() );138 139			// Report this failure back to WordPress.org for debugging purposes.140			wp_version_check(141				array(142					'signature_failure_code' => $download->get_error_code(),143					'signature_failure_data' => $download->get_error_data(),144				)145			);