Ah, I meant it more as a “for your information”. “XDG specification” sounds fancy, but it’s just a description for where programs should put the config files (& other files they might need).
Ah. I was mistaken about ~/.nix-profile and ~/.local/state/nix/profiles.
~/.nix-profile is a convenient symlink to the user’s current profile.
~/.local/state/nix/profiles is just a folder where local profiles can go.
e.g. home manager uses that dir for the home-manager profile.
e.g. you can try readlink ~/.local/state/nix/profiles/home-manager, and this points to e.g. home-manager-15-link.
– You can look through ~/.local/state/nix/profiles/home-manager-15-link or so, you’ll see it has /activate and /bin/home-manager-generation and other files. – When you run home-manager switch, this home-manager profile gets updated to point to a new build.
nix profile install adds a package to the user’s profile. e.g. running nix profile install nixpkgs#cowsay means you’ll have cowsay in ~/.nix-profile/bin.
nix-env --install and nix profile install come with their own footguns. It’s easy to make mistakes when using it that way, causing problems that are difficult to understand (& so are difficult to ask for help for). – It’s often better to just use nix shell nixpkgs#cowsay, or to use Home Manager, or install a system in a global config. – See e.g.