Just dropping a note here for other home-manager users.
If you’re using config.lib.file.mkOutOfStoreSymlink, note that it is currently not compatible with nixpkgs#nixVersions.unstable (i.e. 2.19.2).
The error you see when building your configuration looks like:
error:
… while setting up the build environment
error: getting attributes of path '/nix/store/d5w0zqag0v8wkyab59aph7v9ypkr3h6y-hm_nvim': Permission denied
By default on NixOS you get the stable version (pkgs.nix = pkgs.nixVersions.stable = v2.18.1), unless you have set the option nix.package.
But if you recently installed nix via sh <(curl -L https://nixos.org/nix/install), then you will have 2.19.2.
Work around the issue by removing mkOutOfStoreSymlink from your config, and then downgrading your nix version to nixpkgs#nix (2.18.1, the stable version).
Links to github issues: