Hi Vagrant and Maxim, thanks for the clarification.
I do now see that the latest supported version is rust@1.39.0 om Aarch64 [1]. Thanks also Danny Milosavljevic for blog post on bootstrapping rust [2]. Yes, it's great that Rust is used more, however, at the same time it causes problems integrating it into the Guix system properly. ---- Petr [1] https://github.com/thepowersgang/mrustc [2] https://guix.gnu.org/en/blog/2018/bootstrapping-rust/
