Making patches for overlays?

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1

I’m checking out the overlay page on the nixos wiki, and it refers to making overlays that apply a patch. It gives the example of modifying the package ‘sl’, by adding a ‘patches’ attribute:

final: prev:
{
  sl = prev.sl.overrideAttrs (old: {
    patches = (old.patches or []) ++ [
      (prev.fetchpatch {
        url = "https://github.com/charlieLehman/sl/commit/e20abbd7e1ee26af53f34451a8f7ad79b27a4c0a.patch";
        hash = "07sx98d422589gxr8wflfpkdd0k44kbagxl3b51i56ky2wfix7rc";
      })
      # alternatively if you have a local patch,
      /path/to/file.patch
      # or a relative path (relative to the current nix file)
      ./relative.patch
    ];
  });
}

How does one created a patch of the correct format for that? I’ve tried this before and had it not work. I normally never use patches so that’s unsurprising. How exactly does one make a patch for a package in nixpkgs? I’d probably opt for the relative patch.

My specific need right now is to apply an overlay so that the current yt-dlp package looks like the one from master.

2

You edit the sources, and then use git diff to get a unified diff, which you can then use as a patch for patches.

3

Ok, checked out branc nixpkgs-25.11, copied in the file from master and did

git diff -U > ytpatch

Which yields this file:

diff --git a/pkgs/by-name/yt/yt-dlp/package.nix b/pkgs/by-name/yt/yt-dlp/package.nix
index 5de9b20cc..9178e8c41 100644
--- a/pkgs/by-name/yt/yt-dlp/package.nix
+++ b/pkgs/by-name/yt/yt-dlp/package.nix
@@ -21,14 +21,14 @@ python3Packages.buildPythonApplication rec {
   # The websites yt-dlp deals with are a very moving target. That means that
   # downloads break constantly. Because of that, updates should always be backported
   # to the latest stable release.
-  version = "2026.01.29";
+  version = "2026.01.31";
   pyproject = true;

   src = fetchFromGitHub {
     owner = "yt-dlp";
     repo = "yt-dlp";
     tag = version;
-    hash = "sha256-nw/L71aoAJSCbW1y8ir8obrFPSbVlBA0UtlrxL6YtCQ=";
+    hash = "sha256-3sXXyWuQI6KTOQIkkOfJhCTBBh3Zkv59ENhkrz9Sgxc=";
   };

   postPatch = ''
@@ -51,7 +51,7 @@ python3Packages.buildPythonApplication rec {
   ];

   # expose optional-dependencies, but provide all features
-  dependencies = lib.flatten (lib.attrValues optional-dependencies);
+  dependencies = lib.concatAttrValues optional-dependencies;

   optional-dependencies = {
     default = with python3Packages; [
@@ -100,7 +100,10 @@ python3Packages.buildPythonApplication rec {
         ++ lib.optional rtmpSupport rtmpdump;
     in
     lib.optionals (packagesToBinPath != [ ]) [
-      ''--prefix PATH : "${lib.makeBinPath packagesToBinPath}"''
+      "--prefix"
+      "PATH"
+      ":"
+      ''"${lib.makeBinPath packagesToBinPath}"''
     ];

   checkPhase = ''

Copied that file over to the same dir has my configuration.nix, and added this yt-dlp dealio to this nixpkgs.overlays section:

  nixpkgs.overlays = [ (final: prev: {
    timeclonk = inputs.timeclonk.packages.${pkgs.system}.timeclonk;
    zknotes = inputs.zknotes.packages.${pkgs.system}.zknotes;
    yt-dlp = prev.yt-dlp.overrideAttrs (old: {
      patches = (old.patches or []) ++ [
        ./ytpatch
        ];
      });
  }) ];

now nixos-rebuild yields:

bburdette@HOSS:~/code/bburdette-nix-configs/hoss]$ sudo nixos-rebuild switch --impure
[sudo] password for bburdette:
warning: Git tree '/home/bburdette/code/bburdette-nix-configs' is dirty
building the system configuration...
warning: Git tree '/home/bburdette/code/bburdette-nix-configs' is dirty
evaluation warning: 'system' has been renamed to/replaced by 'stdenv.hostPlatform.system'
error: Cannot build '/nix/store/xa82741jr09blavx17p29vw1dp0pybyw-yt-dlp-2025.12.08.drv'.
       Reason: builder failed with exit code 1.
       Output paths:
         /nix/store/bx0s1fnwhs0zrsg3bgsy0xa4wwic28p4-yt-dlp-2025.12.08-dist
         /nix/store/fx1hkjna8q57b2g5rvwpbbdams72s4p6-yt-dlp-2025.12.08
       Last 25 log lines:
       > Sourcing pypa-install-hook
       > Using pypaInstallPhase
       > Sourcing python-imports-check-hook.sh
       > Using pythonImportsCheckPhase
       > Sourcing python-namespaces-hook
       > Sourcing python-catch-conflicts-hook.sh
       > Running phase: unpackPhase
       > unpacking source archive /nix/store/3424yzpcnz2y3ifypgakm26ghgpyk56s-source
       > source root is source
       > setting SOURCE_DATE_EPOCH to timestamp 315619200 of file "source/yt_dlp/webvtt.py"
       > Running phase: patchPhase
       > applying patch /nix/store/3bwyvwkg5vf0spmjcq2j1xms6b9vx3k1-ytpatch
       > can't find file to patch at input line 5
       > Perhaps you used the wrong -p or --strip option?
       > The text leading up to this was:
       > --------------------------
       > |diff --git a/pkgs/by-name/yt/yt-dlp/package.nix b/pkgs/by-name/yt/yt-dlp/package.nix
       > |index 5de9b20cc..9178e8c41 100644
       > |--- a/pkgs/by-name/yt/yt-dlp/package.nix
       > |+++ b/pkgs/by-name/yt/yt-dlp/package.nix
       > --------------------------
       > File to patch:
       > Skip this patch? [y]
       > Skipping patch.
       > 3 out of 3 hunks ignored
       For full logs, run:
         nix log /nix/store/xa82741jr09blavx17p29vw1dp0pybyw-yt-dlp-2025.12.08.drv
error: Cannot build '/nix/store/q8jpfhccg81ka79ajw664k6qaqnvhn8f-unit-zknotes-onsave.service.drv'.
       Reason: 1 dependency failed.
       Output paths:
         /nix/store/bps632lr1k4a83cdzmmwrgy35mdqfgca-unit-zknotes-onsave.service
error: Cannot build '/nix/store/p1xb8dypsgb8fnrnxy3b6d5dsmqvv721-system-units.drv'.
       Reason: 1 dependency failed.
       Output paths:
         /nix/store/zaw59z7z8w4vq9ip7qzaswaffi6f892w-system-units
error: Cannot build '/nix/store/j3vkc5n5glkbx7jhv5j3fwlcsx6rvq5m-etc.drv'.
       Reason: 1 dependency failed.
       Output paths:
         /nix/store/2z33b2mnd9d87is9fk2i207h7p1x3vxq-etc
error: Cannot build '/nix/store/7scrar2ah3lp4z3dn71l6i7n485z1864-nixos-system-HOSS-25.11.20260128.fa83fd8.drv'.
       Reason: 1 dependency failed.
       Output paths:
         /nix/store/sg1kkdxvz2d4dmmgj3kyzkspvn3s6b2n-nixos-system-HOSS-25.11.20260128.fa83fd8
Command 'nix --extra-experimental-features 'nix-command flakes' build --print-out-paths '/home/bburdette/code/bburdette-nix-configs/hoss#nixosConfigurations."HOSS".config.system.build.toplevel' --no-link --impure' returned non-zero exit status 1.
4

patches is to patch the programs sourcecode. If you want to override the derivations src, then you override the derivations src, not patches. Though as far as I remember, overriding a python packages sources requires some other techniques that I have absolutely no insights into.

1 Like
5

If you’re trying to patch nixpkgs, the way to apply the patch would be using something like pkgs.applyPatches, or using your own custom fork/branch.

In this case I would just use .overridePythonAttrs (equivalent of .overrideAttrs but for python packages) and, yknow, override the attrs that you want to override, don’t use a patch.

1 Like
6

Ok well that explains a lot. I thought the patch the documentation was discussing was for the nix code in nixpkgs, but actually its trying to apply it to the yt-dlp code being fetched from github.

Good to know about .overridePythonAttrs. I got started on modifying the attrs with this but its rather a hassle compared to just diffing a file, IMO. Maybe next time, since I noticed that the yt-dlp version in 25.11 is newer than the version in unstable! I guess unstable isn’t always the latest.

Any any rate, yt-dlp is working again, crisis averted.

7

When a PR is applied to unstable and immediately backported to stable, as happens often with rapidly-moving targets like yt-dlp, it’s fairly common that the change hits stable before unstable, just because unstable often takes longer to make it through CI. It’s a bit counterintuitive, but that’s just how things come out.

1 Like