# Dendritic Pattern
Dendritic is the way to organize your packages in NixOS -- around features. https://github.com/mightyiam/dendritic this is a good example!

# Adding Packages

This configuration is composed from `hosts/opus/default.nix` and focused modules
under `modules/system/` and `modules/features/`. There is no central package list.

## Where a package belongs

| Package type | Module |
| --- | --- |
| Terminal | `modules/features/terminals/default.nix` |
| CLI tool (incl. shell prompts like starship) | `modules/features/cli-tools/default.nix` |
| Editor or IDE | `modules/features/editors/default.nix` |
| Desktop application | `modules/features/desktop-apps/default.nix` |
| Compiler, linter, language tool | `modules/features/dev-tools/default.nix` |
| File manager or archive tool (incl. drag & drop tools) | `modules/features/file-managers/default.nix` |
| Wayland clipboard, screenshot, or input tool | `modules/features/wayland-tools/default.nix` |
| Audio application | `modules/features/audio-tools/default.nix` |
| System monitor or fetch tool | `modules/features/monitoring/default.nix` |
| Font | `modules/features/fonts/default.nix` |
| GStreamer plugin | `modules/features/gst-codecs/default.nix` |
| Runtime library for external binaries | `modules/features/binary-compat/default.nix` |

First use an existing category. Create a new feature module only if the package is
its own service, subsystem, or a group of related packages without a fitting category.

## Add to an existing module

Add the package to that module's `environment.systemPackages` list:

```nix
{ pkgs, ... }:

{
  environment.systemPackages = with pkgs; [
    existing-package
    ripgrep
  ];
}
```

Most modules use `with pkgs;`, so use unqualified package names. Use `pkgs.<name>`
when an explicit path is useful, such as `pkgs.vimPlugins.im-select-nvim`, or when
applying an override:

```nix
(emacs.override { withNativeCompilation = true; })
```

Keep related packages together and follow the local ordering of the file.

## Fonts are different

Fonts belong in `modules/features/fonts/default.nix` under `fonts.packages`, not
`environment.systemPackages`:

```nix
fonts.packages = with pkgs; [
  nerd-fonts.jetbrains-mono
  noto-fonts-color-emoji
];
```

## Create a new feature module

1. Create `modules/features/<category>/default.nix`:

   ```nix
   { pkgs, ... }:

   {
     environment.systemPackages = with pkgs; [
       package-name
     ];
   }
   ```

2. Add its directory to the `imports` list in `hosts/opus/default.nix`:

   ```nix
   ../../modules/features/<category>
   ```

3. Put services and program options in the same module when they belong to that
   feature, as done by `modules/features/mpd/default.nix`.

## Host-only packages

For a package that is truly specific to this desktop, add it to the small
`environment.systemPackages` list in `hosts/opus/default.nix`. Gaming is the current
example. If that list starts to represent a reusable category, extract a feature module.

## Packages from flake inputs

Packages provided by a flake input use `inputs` and the host platform, following
`modules/features/desktop-apps/default.nix`:

```nix
{ pkgs, inputs, ... }:

{
  environment.systemPackages = with pkgs; [
    inputs.helium-browser.packages.${pkgs.stdenv.hostPlatform.system}.helium
  ];
}
```

If an input provides a NixOS module, import it in the feature module, following
`modules/features/noctalia-greeter/default.nix`:

```nix
imports = [
  inputs.some-input.nixosModules.default
];
```

The input itself must first be declared in `flake.nix`.

## Build and switch

From the `nixos/` directory, first test that the configuration evaluates and builds:

```bash
doas nixos-rebuild build --flake .#opus
```

Then activate it:

```bash
doas nixos-rebuild switch --flake .#opus
```

If a terminal's font icons do not update after adding fonts, restart the terminal or
log out and back in after the switch.