fn check_makefile_min_version(external_descriptor: &str) -> Result<(), CargoMakeError> {
    let value: toml::Value = match toml::from_str(&external_descriptor) {
        Ok(value) => value,
        // If there's an error parsing the file, let the caller function figure
        // it out
        Err(_) => return Ok(()),
    };

    let min_version = value
        .get("config")
        .and_then(|config| config.get("min_version"))
        .and_then(|min_ver| min_ver.as_str());

    if let Some(ref min_version) = min_version {
        if version::is_newer_found(&min_version) {
            return Err(CargoMakeError::VersionTooOld(min_version.to_string()));
        }
    }

    Ok(())
}
Ensure the Makefile's min_version, if present, is older than cargo-make's
currently running version.
src/lib/descriptor/mod.rs