A home-manager directory that auto-creates dotfile symlinks to it in `~/.config/` based on the file structure

auto-symlinking-nix-directory.md

The function below lets you create a directory in your home-manager config that auto-creates symlinks for non-Nix dotfiles from ~/.config/ using xdg.configFile and mkOutOfStoreSymlink. This gives the following advantages:

1. You can keep all your non-Nix dotfiles in your home-manager repo.
2. You don't have to do home-manager switch on each dotfile change. Changes are instantly reflected.
3. You don't need to hard-code the paths for each symlink, the linking is instead file-based. Just add the new dotfile to the directory, and you're done.

For example, if your home-manager config is in ~/nixos/ and looks like this...:

~/nixos
├── ...
├── flake.nix
└── configs
    ├── starship.toml
    └── fish
        └── config.fish

...then home-mamager will create the following symlinks in ~/.config:

~/.config
├── ...
├── starship.toml -> ~/nixos/configs/starship.toml
└── fish
    └── config.fish -> ~/nixos/configs/fish/config.fish

Don't forget to git add when adding a new dotfile. Otherwise, they will be ignored by Nix. Then run home-manager switch to create the new symlink.

{ config }:
{
  # -------------------------------------------------------------------------
  #   `configsPath`: a path value to a directory who's files/directories
  #   should be symlinked to from `~/.config/`.
  #
  #   `configsAbsolutePath`: an absolute path to `configsPath`.
  #
  #   The reason this function requires two path parameters to the same
  #   directory is that it uses `builtins.readDir` which would require
  #   `--impure` if only an absolute path were used. If using only a literal
  #   Nix path, the symlinks would point to the Nix store, and thereby require
  #   a build whenever a config file is edited.
  #
  #   `returns`: an attribute set suitable for `xdg.configFile`.
  # -----------------------------------------------------------------
  configSymlinks = configsPath: configsAbsolutePath:
    let
      inherit (config.lib.file) mkOutOfStoreSymlink;

      mkSymlink = name: {
        name = name;
        value.source = mkOutOfStoreSymlink "${configsAbsolutePath}/${name}";
      };
    in configsPath
      |> builtins.readDir
      |> builtins.attrNames
      |> map mkSymlink
      |> builtins.listToAttrs;
}

You call the function like this:

# Both arguments should point to your `configs` directory in home-manager. The
# first is relative to this file, the second is the absolute path.
xdg.configFile = configs.configSymlinks ./configs "~/nixos/configs/";

Please let me know if there's some way to improve the implementation so that you only have to pass in one path parameter.