wikimedia / mediawiki

		$cache = isset( $this->sessionFieldCache[$id] ) ? $this->sessionFieldCache[$id] : [];

		foreach ( $data as $key => $value ) {

			if ( !array_key_exists( $key, $cache ) ) {

				if ( $session->exists( $key ) ) {

					// New in both, so ignore and log

					$this->logger->warning(

						__METHOD__ . ": Key \"$key\" added in both Session and \$_SESSION!"

					);

				} else {

					// New in $_SESSION, keep it

					$session->set( $key, $value );

					$changed = true;

				}

			} elseif ( $cache[$key] === $value ) {

				// Unchanged in $_SESSION, so ignore it

			} elseif ( !$session->exists( $key ) ) {

				}

			} elseif ( $cache[$key] === $value ) {

				// Unchanged in $_SESSION, so ignore it

			} elseif ( !$session->exists( $key ) ) {

				// Deleted in Session, keep but log

				$this->logger->warning(

					__METHOD__ . ": Key \"$key\" deleted in Session and changed in \$_SESSION!"

				);

				$session->set( $key, $value );

				$changed = true;

			} elseif ( $cache[$key] === $session->get( $key ) ) {

				// Unchanged in Session, so keep it

				$session->set( $key, $value );

				$changed = true;