Automatic (shell) completions for devShell (zsh or in general)

When I get dropped into a devShell, which is based on the devShell I define in a flake.nix and direnv “activates” it for me, certain tools have working (auto-)completions and certain tools do not. I was not able to figure out on a surface-level, how I would/should fix this. Since I work a lot with Rust projects I added this for cargo / (oxalica/crane) related tooling. devShells.default = craneLib.devShell ( { shellHook = '' export FPATH="${toolchain...