FWIW, I don't think it's nice that rustup fetches and installs new versions without prompting, but I suppose that other users like it or get used to it. Fortunately most Rust projects work on any recently stable version.

> 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.

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.

Node do allow you to declare what node version supported in your package.json. The definition is there, but there isn't any tool that read the declaration and switch to it accordingly. I feel it is somewhat half-assed. But is could also caused by the fact the entity that distribute the package (npm) and node binaries (various of linux repository) isn't the same group of people. So there isn't really anyone can do anything about it unless we get something like corepack someday. (probably someone should name it 'corenode' ?)