[super_flanker]

> rustup fetches and installs new versions without prompting

I don't think it's true. rustup installs new version only when you run `rustup update`. What parent is talking about is pinning a particular rustc version in Cargo.toml, which allows rustup to download that version of rustc to build that particular project/crate.

[kzrdude]

rustup will automatically download that version when you interact with that project, though, and that's what I mean. It doesn't sit right with me, comes as a surprise, but I guess it's not the biggest issue in the world.