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→‎Overriding a package inside a scope
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(Copy-pasta from discourse, at some point someone should clean)
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<blockquote>Overlays are Nix functions which accept two arguments, conventionally called <code>final</code> and <code>prev</code> (formerly also <code>self</code> and <code>super</code>), and return a set of packages. ... Overlays are similar to other methods for customizing Nixpkgs, in particular the packageOverrides ... Indeed, packageOverrides acts as an overlay with only the <code>prev</code> (<code>super</code>) argument. It is therefore appropriate for basic use, but overlays are more powerful and easier to distribute.</blockquote>
<cite>From the [https://nixos.org/manual/nixpkgs/stable/#sec-overlays-definition Nixpkgs manual]</cite>
Overlays provide a method to extend and change nixpkgs. They replace constructs like <code>packageOverride</code> and <code>overridePackages</code>.
Overlays provide a method to extend and change nixpkgs. They replace constructs like <code>packageOverride</code> and <code>overridePackages</code>.


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<syntaxhighlight lang="nix">
<syntaxhighlight lang="nix">
let overlay1 = self: super:
final: prev: {
{
   google-chrome = prev.google-chrome.override {
   google-chrome = super.google-chrome.override {
     commandLineArgs =
     commandLineArgs =
       "--proxy-server='https=127.0.0.1:3128;http=127.0.0.1:3128'";
       "--proxy-server='https=127.0.0.1:3128;http=127.0.0.1:3128'";
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== Data flow of overlays ==
== Data flow of overlays ==


The data flow around overlays, especially regarding <tt>super</tt> and <tt>self</tt> arguments can be a bit confusing if you are not familiar with how overlays work. This graph shows the data flow:
The data flow of overlays, especially regarding <tt>prev</tt> and <tt>final</tt> arguments can be a bit confusing if you are not familiar with how overlays work. This graph shows the data flow:


[[File:Dram-overlay-self-super.png]]
[[File:Dram-overlay-final-prev.png]]


Here the main package set is extended with two overlays, ext-1 and ext-2. <tt>x // y</tt> is represented by a <tt>//</tt> box with <tt>x</tt> coming in from the left and <tt>y</tt> from above.
Here the main package set is extended with two overlays, ext-1 and ext-2. <tt>x // y</tt> is represented by a <tt>//</tt> box with <tt>x</tt> coming in from the left and <tt>y</tt> from above.


As you can see, <tt>self</tt> is the same for every stage, but <tt>super</tt> comes from only the stage before. So when you define an attribute <tt>foo</tt> in the set to override it, within that overlay <tt>self.foo</tt> will be it's version, and <tt>super.foo</tt> will be the non-overriden version. This is why you see patterns like <tt>foo = super.foo.override { ... }</tt>.
As you can see, <tt>final</tt> is the same for every stage, but <tt>prev</tt> comes from only the stage before. So when you define an attribute <tt>foo</tt> in the set to override it, within that overlay <tt>final.foo</tt> will be its version, and <tt>prev.foo</tt> will be the non-overriden version. This is why you see patterns like <tt>foo = prev.foo.override { ... }</tt>.


The names <tt>self</tt> and <tt>super</tt> might remind you of inheritance in object-oriented languages. In fact, overlays are exactly the same thing as subclasses, with regards to overriding and calling methods. This data flow is also how objects know which method to call. This is probably why the two arguments got their names, too.
The names <tt>final</tt> and <tt>prev</tt> might remind you of inheritance in object-oriented languages. In fact, overlays are exactly the same thing as subclasses, with regards to overriding and calling methods. This data flow is also how objects know which method to call. This is probably how the two arguments got their names, too.


== Data flow of overlays (Better explanation???) ==
== Data flow of overlays (alternative explanation) ==
Source: https://discourse.nixos.org/t/how-to-exclude-packages/13039/4
Source: https://discourse.nixos.org/t/how-to-exclude-packages/13039/4


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And `final: prev: firefox = final.firefox.override { ... };` would cause infinite recursion.
And <syntaxhighlight lang="nix">final: prev: { firefox = final.firefox.override { ... }; }</syntaxhighlight> would cause infinite recursion.


== Using overlays ==
== Using overlays ==
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==== In standalone nix code ====
==== In standalone nix code ====
===== In a shell.nix =====
When writing standalone nix code, for example a <code>shell.nix</code> for a project, one usually starts by importing nixpkgs: <code>let pkgs = import <nixpkgs> {}</code>. To use an overlay in this context, replace that by:
When writing standalone nix code, for example a <code>shell.nix</code> for a project, one usually starts by importing nixpkgs: <code>let pkgs = import <nixpkgs> {}</code>. To use an overlay in this context, replace that by:
<syntaxhighlight lang="nix">
<syntaxhighlight lang="nix">
import <nixpkgs> { overlays = [ overlay1 overlay2 ]; }
import <nixpkgs> { overlays = [ overlay1 overlay2 ]; }
</syntaxhighlight>
===== In a Nix flake =====
In a Nix flake, nixpkgs will be coming from the inputs. It is common to write something like
<syntaxhighlight lang="nix">
let pkgs = nixpkgs.legacyPackages.${system}
</syntaxhighlight>
where <code>system</code> is a variable containing eg. <code>"x86_64-linux"</code>. In order to apply overlays to this, one can do either of:
<syntaxhighlight lang="nix">
let pkgs = (nixpkgs.legacyPackages.${system}.extend overlay1).extend overlay2
</syntaxhighlight>
or, using the <code>import</code> function:
<syntaxhighlight lang="nix">
let pkgs = import nixpkgs { inherit system; overlays = [ overlay1 overlay2 ]; }
</syntaxhighlight>
</syntaxhighlight>


Line 59: Line 80:
{
{
   # [...]
   # [...]
   nixpkgs.overlays = [ (self: super: /* overlay goes here */) ];
   nixpkgs.overlays = [ (final: prev: /* overlay goes here */) ];
}
}
</syntaxhighlight>
</syntaxhighlight>
Line 74: Line 95:
{
{
   # [...]
   # [...]
   nixpkgs.overlays = [ (self: super: /* overlay goes here */) ];
   nixpkgs.overlays = [ (final: prev: /* overlay goes here */) ];
}
}
</syntaxhighlight>
</syntaxhighlight>
Line 120: Line 141:
   nix.nixPath =
   nix.nixPath =
     # Prepend default nixPath values.
     # Prepend default nixPath values.
     options.nix.nixPath.default ++  
     options.nix.nixPath.default ++
     # Append our nixpkgs-overlays.
     # Append our nixpkgs-overlays.
     [ "nixpkgs-overlays=/etc/nixos/overlays-compat/" ]
     [ "nixpkgs-overlays=/etc/nixos/overlays-compat/" ]
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</syntaxhighlight>
</syntaxhighlight>


Then, add the following contents to <tt>/etc/nixos/overlays-compat/overlays.nix</tt><ref>Based on [https://gitlab.com/samueldr/nixos-configuration/blob/3febd83b15210282d6435932944d426cd0a9e0ca/modules/overlays-compat/overlays.nix [[User:samueldr|@samueldr]]'s configuration: overlays-compat]</ref>:
Then, add the following contents to <tt>/etc/nixos/overlays-compat/overlays.nix</tt><ref>Based on [https://gitlab.com/samueldr/nixos-configuration/blob/3febd83b15210282d6435932944d426cd0a9e0ca/modules/overlays-compat/overlays.nix][[User:Samueldr|@samueldr]]<span>'s configuration: overlays-compat</span></ref>:


<syntaxhighlight lang="nix">
<syntaxhighlight lang="nix">
self: super:
final: prev:
with super.lib;
with prev.lib;
let
let
   # Load the system config and get the `nixpkgs.overlays` option
   # Load the system config and get the `nixpkgs.overlays` option
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in
in
   # Apply all overlays to the input of the current "main" overlay
   # Apply all overlays to the input of the current "main" overlay
   foldl' (flip extends) (_: super) overlays self
   foldl' (flip extends) (_: prev) overlays final
</syntaxhighlight>
</syntaxhighlight>


The <tt>/etc/nixos/overlays-compat</tt> directory should contain a single <tt>overlays.nix</tt> file to be understood by the Nix tooling, but the location of this directory can be arbitrary, as long as it is set correctly in the <code>nix.nixPath</code> option.
The <tt>/etc/nixos/overlays-compat</tt> directory should contain a single <tt>overlays.nix</tt> file to be understood by the Nix tooling, but the location of this directory can be arbitrary, as long as it is set correctly in the <code>nix.nixPath</code> option.


== External Documentation ==
* [https://nixos.org/nixpkgs/manual/#chap-overlays Overlays  in nixpkgs manual]
* [https://blog.flyingcircus.io/2017/11/07/nixos-the-dos-and-donts-of-nixpkgs-overlays/ Blog post "The DOs and DON’Ts of nixpkgs overlays"]
== Examples of overlays ==
== Examples of overlays ==
Here are a few example usages of overlays.
Here are a few example usages of overlays.
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This method will fail if the build system changed or new dependencies are required.
This method will fail if the build system changed or new dependencies are required.
<syntaxhighlight lang="nix">
<syntaxhighlight lang="nix">
self: super:
final: prev:
{
{
   sl = super.sl.overrideAttrs (old: {
   sl = prev.sl.overrideAttrs (old: {
     src = super.fetchFromGitHub {
     src = prev.fetchFromGitHub {
       owner = "mtoyoda";
       owner = "mtoyoda";
       repo = "sl";
       repo = "sl";
       rev = "923e7d7ebc5c1f009755bdeb789ac25658ccce03";
       rev = "923e7d7ebc5c1f009755bdeb789ac25658ccce03";
       # If you don't know the hash, the first time, set:
       # If you don't know the hash, the first time, set:
       # sha256 = "0000000000000000000000000000000000000000000000000000";
       # hash = "";
       # then nix will fail the build with such an error message:
       # then nix will fail the build with such an error message:
       # hash mismatch in fixed-output derivation '/nix/store/m1ga09c0z1a6n7rj8ky3s31dpgalsn0n-source':
       # hash mismatch in fixed-output derivation '/nix/store/m1ga09c0z1a6n7rj8ky3s31dpgalsn0n-source':
       # wanted: sha256:0000000000000000000000000000000000000000000000000000
       # specified: sha256-AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA=
       # got:    sha256:173gxk0ymiw94glyjzjizp8bv8g72gwkjhacigd1an09jshdrjb4
       # got:    sha256-173gxk0ymiw94glyjzjizp8bv8g72gwkjhacigd1an09jshdrjb4
       sha256 = "173gxk0ymiw94glyjzjizp8bv8g72gwkjhacigd1an09jshdrjb4";
       hash = "173gxk0ymiw94glyjzjizp8bv8g72gwkjhacigd1an09jshdrjb4";
     };
     };
   });
   });
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It is easy to add patches to a nix package:
It is easy to add patches to a nix package:
<syntaxhighlight lang="nix">
<syntaxhighlight lang="nix">
self: super:
final: prev:
{
{
   sl = super.sl.overrideAttrs (old: {
   sl = prev.sl.overrideAttrs (old: {
     patches = (old.patches or []) ++ [
     patches = (old.patches or []) ++ [
       (super.fetchpatch {
       (prev.fetchpatch {
         url = "https://github.com/charlieLehman/sl/commit/e20abbd7e1ee26af53f34451a8f7ad79b27a4c0a.patch";
         url = "https://github.com/charlieLehman/sl/commit/e20abbd7e1ee26af53f34451a8f7ad79b27a4c0a.patch";
         sha256 = "07sx98d422589gxr8wflfpkdd0k44kbagxl3b51i56ky2wfix7rc";
         hash = "07sx98d422589gxr8wflfpkdd0k44kbagxl3b51i56ky2wfix7rc";
       })
       })
       # alternatively if you have a local patch,  
       # alternatively if you have a local patch,
       /path/to/file.patch
       /path/to/file.patch
       # or a relative path (relative to the current nix file)
       # or a relative path (relative to the current nix file)
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Some packages provide compilation options. Those are not easily disoverable; to find them you need to have a look at the source. For example, with <code>nix edit -f "<nixpkgs>" pass</code> one can see that pass can be compiled with or without dependencies on X11 with the <code>x11Support</code> argument. Here is how you can remove X11 dependencies:
Some packages provide compilation options. Those are not easily disoverable; to find them you need to have a look at the source. For example, with <code>nix edit -f "<nixpkgs>" pass</code> one can see that pass can be compiled with or without dependencies on X11 with the <code>x11Support</code> argument. Here is how you can remove X11 dependencies:
<syntaxhighlight lang="nix">
<syntaxhighlight lang="nix">
self: super:
final: prev:
{
{
   pass = super.pass.override { x11Support = false; };  
   pass = prev.pass.override { x11Support = false; };
}
}
</syntaxhighlight>
</syntaxhighlight>


=== Overriding a package inside a scope ===
=== Overriding a package inside a scope ===
Some packages are not in the top level of nixpkgs but inside a ''scope''. For example all [[GNOME]] packages are in the <code>gnome3</code> attribute set and [[Xfce]] packages inside <code>xfce</code>. These attributes are often ''scopes'' and must be overriden specially. Here is an example of patching <code>xfce.xfce4-terminal</code>.
Some packages are not in the top level of nixpkgs but inside a ''scope''. For example all [[GNOME]] packages are in the <code>gnome</code> attribute set and [[Xfce]] packages inside <code>xfce</code>. These attributes are often ''scopes'' and must be overriden specially. Here is an example of patching <code>gnome.mutter</code> and <code>gnome.gnome-control-center</code>.
<syntaxhighlight lang="nix">
# elements of nixpkgs must be taken from final and prev
final: prev: {
  # elements of pkgs.gnome must be taken from gfinal and gprev
  gnome = prev.gnome.overrideScope (gfinal: gprev: {
    mutter = gprev.mutter.overrideAttrs (oldAttrs: {
      patches = oldAttrs.patches ++ [
        # https://salsa.debian.org/gnome-team/mutter/-/blob/ubuntu/master/debian/patches/x11-Add-support-for-fractional-scaling-using-Randr.patch
        (prev.fetchpatch {
          url = "https://salsa.debian.org/gnome-team/mutter/-/raw/91d9bdafd5d624fe1f40f4be48663014830eee78/debian/patches/x11-Add-support-for-fractional-scaling-using-Randr.patch";
          hash = "m6PKjVxhGVuzsMBVA82UyJ6Cb1s6SMI0eRooa+F2MY8=";
        })
    ];
    });
    gnome-control-center = gprev.gnome-control-center.overrideAttrs (oldAttrs: {
      patches = oldAttrs.patches ++ [
        # https://salsa.debian.org/gnome-team/gnome-control-center/-/blob/ubuntu/master/debian/patches/ubuntu/display-Support-UI-scaled-logical-monitor-mode.patch
        (prev.fetchpatch {
          url = "https://salsa.debian.org/gnome-team/gnome-control-center/-/raw/f185f33fb200cc963c062c7a82920a085f696978/debian/patches/ubuntu/display-Support-UI-scaled-logical-monitor-mode.patch";
          hash = "XBMD0chaV6GGg3R9/rQnsBejXspomVZz/a4Bvv/AHCA=";
        })
        # https://salsa.debian.org/gnome-team/gnome-control-center/-/blob/ubuntu/master/debian/patches/ubuntu/display-Allow-fractional-scaling-to-be-enabled.patch
        (prev.fetchpatch {
          url = "https://salsa.debian.org/gnome-team/gnome-control-center/-/raw/f185f33fb200cc963c062c7a82920a085f696978/debian/patches/ubuntu/display-Allow-fractional-scaling-to-be-enabled.patch";
          hash = "Pm6PTmsL2bW9JAHD1u0oUEqD1PCIErOlcuqlwvP593I=";
        })
      ];
    });
  });
}
</syntaxhighlight>
 
=== Overriding a package inside an extensible attribute set ===
 
Here is an example of adding plugins to `vimPlugins`.
<syntaxhighlight lang="nix">
<syntaxhighlight lang="nix">
# elements of nixpkgs must be taken from self and super
final: prev: {
self: super:
   vimPlugins = prev.vimPlugins.extend (final': prev': {
{
    indent-blankline-nvim-lua = prev.callPackage ../packages/indent-blankline-nvim-lua { };
   xfce = super.xfce.overrideScope' (
  });
    # elements of pkgs.xfce must be taken from selfx and superx
    selfx: superx: {
      xfce4-terminal = superx.xfce4-terminal.overrideAttrs (
        old: {
          patches = (old.patches or []) ++ [
            (
              # https://bugzilla.xfce.org/show_bug.cgi?id=16682
              super.fetchpatch {
                url = "https://bugzilla.xfce.org/attachment.cgi?id=9709";
                sha256 = "1shxzzvwsybri772lbm17rpd1l0g9y2vc7f7xgqlgkgz72wzr5zp";
              }
            )
          ];
        }
      );
    }
  );
}
}
</syntaxhighlight>
=== Overrding a package inside a plain attribute set ===
Here's an example of overriding the source of <code>obs-studio-plugins.obs-backgroundremoval</code>.
<syntaxhighlight lang="nix">
    final: prev: {
      obs-studio-plugins = prev.obs-studio-plugins // {
        obs-backgroundremoval =
          prev.obs-studio-plugins.obs-backgroundremoval.overrideAttrs (old: {
            version = "0.5.17";
            src = prev.fetchFromGitHub {
              owner = "royshil";
              repo = "obs-backgroundremoval";
              rev = "v0.5.17";
              hash = "";
            };
          });
      };
    };
</syntaxhighlight>
</syntaxhighlight>


Line 232: Line 288:
=== Python Packages Overlay ===
=== Python Packages Overlay ===


Here is an example of Python packages overlay. The trick is to also override python itself with `packageOverrides`.
Here is an example of Python packages overlay. The trick is to also override python itself with <code>packageOverrides</code>.


Github issue with the snippet below: [[https://github.com/NixOS/nixpkgs/issues/26487#issuecomment-307363295]]
Github issue with the snippet below: [[https://github.com/NixOS/nixpkgs/issues/26487#issuecomment-307363295]]


<syntaxhighlight lang="nix">
<syntaxhighlight lang="nix">
self: super:
final: prev:
# Within the overlay we use a recursive set, though I think we can use `self` as well.
# Within the overlay we use a recursive set, though I think we can use `final` as well.
rec {
rec {
   # nix-shell -p python.pkgs.my_stuff
   # nix-shell -p python.pkgs.my_stuff
   python = super.python.override {
   python = prev.python.override {
     # Careful, we're using a different self and super here!
     # Careful, we're using a different final and prev here!
     packageOverrides = self: super: {
     packageOverrides = final: prev: {
       my_stuff = super.buildPythonPackage rec {
       my_stuff = prev.buildPythonPackage rec {
         pname = "pyaes";
         pname = "pyaes";
         version = "1.6.0";
         version = "1.6.0";
         src = super.fetchPypi {
         src = prev.fetchPypi {
           inherit pname version;
           inherit pname version;
           sha256 = "0bp9bjqy1n6ij1zb86wz9lqa1dhla8qr1d7w2kxyn7jbj56sbmcw";
           hash = "0bp9bjqy1n6ij1zb86wz9lqa1dhla8qr1d7w2kxyn7jbj56sbmcw";
         };
         };
       };
       };
Line 263: Line 319:
     src = pythonPackages.fetchPypi {
     src = pythonPackages.fetchPypi {
       inherit pname version;
       inherit pname version;
       sha256 = "0bp9bjqy1n6ij1zb86wz9lqa1dhla8qr1d7w2kxyn7jbj56sbmcw";
       hash = "0bp9bjqy1n6ij1zb86wz9lqa1dhla8qr1d7w2kxyn7jbj56sbmcw";
    };
  };
}
</syntaxhighlight>
 
 
=== R Packages Overlay ===
 
Here is an example of an R packages overlay, in which it can be seen how to provide different versions of packages then those available in the current R version. It should be noted that in the case of R and Python the argument to <code>override</code> is named differently. Names of these can be found using <code>nix repl</code> and evaluating e.g. <code>python.override.__functionArgs</code>.
 
<syntaxhighlight lang="nix">
final: prev:
 
{
  rPackages = prev.rPackages.override {
    overrides = {
 
      rprojroot = prev.rPackages.buildRPackage rec {
        name = "rprojroot-${version}";
        version = "2.0.2";
        src = prev.fetchurl {
          url =
            "https://github.com/r-lib/rprojroot/archive/refs/tags/v2.0.2.tar.gz";
          hash = "1i0s1f7hla91yw1fdx0rn7c18dp6jwmg2mlww8dix1kk7qbxfjww";
        };
        nativeBuildInputs = [ prev.R ];
      };
 
      here = prev.rPackages.buildRPackage rec {
        name = "here-${version}";
        version = "1.0.1";
        src = prev.fetchurl {
          url = "https://github.com/r-lib/here/archive/refs/tags/v1.0.1.tar.gz";
          hash = "0ky6sq6n8px3b70s10hy99sccf3vcjjpdhamql5dr7i9igsf8nqy";
        };
        nativeBuildInputs = [ prev.R final.rPackages.rprojroot ];
        propagatedBuildInputs = [ final.rPackages.rprojroot ];
      };
     };
     };
   };
   };
}
}
</syntaxhighlight>
</syntaxhighlight>
=== Rust packages ===
Due to https://github.com/NixOS/nixpkgs/issues/107070
it is not possible to just override <code>cargoHash</code>, instead cargoDeps has to be overriden
<syntaxhighlight lang="nix">
final: prev: {
  rnix-lsp = prev.rnix-lsp.overrideAttrs (oldAttrs: rec {
    version = "master";
 
    src = prev.fetchFromGitHub {
      owner = "nix-community";
      repo = "rnix-lsp";
      rev = "1fdd7cf9bf56b8ad2dddcfd27354dae8aef2b453";
      hash = "sha256-w0hpyFXxltmOpbBKNQ2tfKRWELQzStc/ho1EcNyYaWc=";
    };
 
    cargoDeps = oldAttrs.cargoDeps.overrideAttrs (lib.const {
      name = "rnix-lsp-vendor.tar.gz";
      inherit src;
      outputHash = "sha256-6ZaaWYajmgPXQ5sbeRQWzsbaf0Re3F7mTPOU3xqY02g=";
    });
  });
}
</syntaxhighlight>
== List of 3rd party overlays ==
This is an non-exhaustive list:
* [https://nixos.org/manual/nixpkgs/unstable/#using-community-maintained-rust-toolchains Details in the Nixpkgs manual for using Rust overlays]
* [https://github.com/peter-sa/nixos-rocm Overlay for Radeon Open-Compute packages]
* [https://github.com/garbas/nixpkgs-python Overlay by Rok Garbas for a set of python packages built by pypi2nix (archived)]
== See also ==
* [https://nixos.org/nixpkgs/manual/#chap-overlays Overlays  in nixpkgs manual]
* [https://blog.flyingcircus.io/2017/11/07/nixos-the-dos-and-donts-of-nixpkgs-overlays/ Blog post "The DOs and DON’Ts of nixpkgs overlays"]
* [https://www.youtube.com/watch?v=s2fkgkN55vk&list=PLgknCdxP89ReD6gxl755B6G_CI65z4J2e Nixpkgs Overlays – A place for all excluded packages] - Talk by Nicolas B. Pierron at NixCon 2017


==== References ====
==== References ====
[[Category:Cookbook]]
[[Category:Nixpkgs]]
Nanotwerp
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