Right, so if I'm understanding correctly, I'd need to pin the whole nix-pkgs system to the particular git revision which contains the version I need?

That's it, also you can cherry pick different software from different git revisions.

Do you have any public examples of doing this? Or docs?

Closest I found was to pin the nix-channel entirely, but not different components to different versions.

You could do something like:

    let pinnedPkgs = import (builtins.fetchTarball {...}) {};
        node = pinnedPkgs.nodejs-10_x;

to refer to a specific version of node.

https://nixos.wiki/wiki/FAQ/Pinning_Nixpkgs

Thanks that helps.

I've mostly stuck to nix-shell -p foo bar baz to setup my environments. It's holding me back and I should pull the trigger on a shell.nix file, just gotta learn the language.