/**
     * Gets the user Toolchains source.
     *
     * @return the user Toolchains source or {@code null} if none
     */
    @Nonnull
    Optional<Source> getUserToolchainsSource();

    @Nonnull
    static ToolchainsBuilderRequest build(
            @Nonnull ProtoSession session,
            @Nullable Source installationToolchainsFile,
            @Nullable Source userToolchainsSource) {