* directory pointed at by the {@code -f/--file} command line argument.
     *
     * @return the directory of the topmost project, never {@code null}
     * @see Project#isTopProject()
     * @see #getRootDirectory()
     */
    @Nonnull
    Path getTopDirectory();

    /**
     * Gets the root directory of the session, which is the root directory for the top directory project.