# Packages
Similar to [modules](../modules), the pkgs directory mirrors the upstream
[nixpkgs/pkgs][pkgs], and for the same reason; if you ever want to upstream
your package, it's as simple as dropping it into the nixpkgs/pkgs directory.

The only minor difference is that, instead of adding the `callPackage` call to
`all-packages.nix`, you just add it the the _default.nix_ in this directory,
which is defined as a simple overlay.

This overlay is set as the default `overlay` output attribute for the flake.
And all the packages are exported via `packages.<system>.<pkg-name>`, for all
the supported systems listed in the package's `meta.platforms` attribute.

And, as usual, every package in the overlay is also available to any NixOS
[host](../hosts).

## Automatic Source Updates
There is the added, but optional, convenience of declaring your sources in
_pkgs/flake.nix_ as an input. This allows updates to be managed automatically
by simply [updating](../doc/flk/update.md#updating-package-sources) the lock
file. No more manually entering sha256 hashes!


## Example
pkgs/development/libraries/libinih/default.nix:
```nix
{ stdenv, meson, ninja, lib, srcs, ... }:
let version = "r53";
in
stdenv.mkDerivation {
  pname = "libinih";
  inherit version;

  src = srcs.libinih;

  buildInputs = [ meson ninja ];

  mesonFlags = ''
    -Ddefault_library=shared
    -Ddistro_install=true
  '';

  meta = with lib; {
    description = "Simple .INI file parser in C";
    homepage = "https://github.com/benhoyt/inih";
    maintainers = [ maintainers.divnix ];
    license = licenses.bsd3;
    platforms = platforms.all;
    inherit version;
  };
}
```

pkgs/default.nix:
```nix
final: prev: {
  libinih = prev.callPackage ./development/libraries/libinih { };
}
```

pkgs/flake.nix:
```nix
{
  description = "Package sources";

  inputs = {
    libinih.url = "github:benhoyt/inih/r53";
    libinih.flake = false;
  };
}
```

[pkgs]: https://github.com/NixOS/nixpkgs/tree/master/pkgs