nixos/nixpkgs.config: make use of the module defined in config.nix by jopejoe1 · Pull Request #489889 · NixOS/nixpkgs

jopejoe1 · 2026-02-12T19:12:59Z

This makes it so that the nixpkgs.config options can be merged with the module system

It also makes the defined options show up in search and the manual.

closes #368051
closes #468647
closes #356739
closes #330627

Things done

These are handled in the NixOS modules for `nixpkgs.config` as special merges; add them here.

Makes it possible to render it in the NixOS manual, as that one does not contain the Nixpkgs manual specific ones.

This makes it so that the `nixpkgs.config` options can be merged with the module system It also makes the defined options show up in search and the manual.

jopejoe1 · 2026-02-13T10:26:20Z

pkgs/top-level/config.nix

+}@args:

 let
+  docPrefix = args.docPrefix or "";


Not happy about all the docPrefix, but it works if someone has a better idea please let me know.

You can't do . or or ? on module arguments directly, because they're generated from the individual module's functionArgs. (otherwise a { ... }: function is by definition strict, ie not lazy like it needs to be)
This should work though:

Suggested change

docPrefix = args.docPrefix or "";

docPrefix = config._module.args.docPrefix or "";

wolfgangwalther · 2026-02-13T13:20:06Z

Love the direction of this PR; I just hit the inability to merge nixpkgs config entries earlier this weeks. Won't have time to review this, though.

dwt · 2026-02-14T08:41:25Z

This is super interesting. I briefly tried this and didn't get very far with my last pull request touching this area. My work did include some tests because I didn't particularly trust myself with the intricacies of this code. Did they happen to survive this change intact? (I'll look into this later, but quite busy, so no definite timescale given)

dwt · 2026-02-14T15:04:22Z

As far as I can tell my tests still work.

This brings me to the next question: Do you have any idea why this was not done in the first place? I always assumed that this might have something to do with importing multiple nixpkgs versions, but sharing the config object between them, and that for that reason it needed to be dumb and not part of the module system.

But I did not find any documentation or comments that clarified this.

jopejoe1 · 2026-02-16T15:01:18Z

As far as I can tell, the nixpkgs.config was added before config was made into a module, so I think no one came around to ever changing it to make use of this module. Maybe someone like @roberth who has more insight into the module system, would know.

SuperSandro2000 · 2026-02-19T22:17:08Z

noice! Looking forward to this being merged!

philiptaron

Diff looks good to me; every time we have tried to add an option in this way, we've had to do a tree wide to find every user of it and adapt them from the or null pattern. I do expect that because this allows setting the default, there's going to be a set of places that need updating in that way. The second thing that's been run into with similar PRs is that there are many doors into Nixpkgs, and not everyone has this logic.

dwt · 2026-02-22T09:59:39Z

Diff looks good to me; every time we have tried to add an option in this way, we've had to do a tree wide to find every user of it and adapt them from the or null pattern. I do expect that because this allows setting the default, there's going to be a set of places that need updating in that way. The second thing that's been run into with similar PRs is that there are many doors into Nixpkgs, and not everyone has this logic.

Do you have any links / examples for this, so we can understand how this breaks or would break existing configurations?

philiptaron · 2026-02-22T14:41:29Z

I'm on mobile so search is hard. I think this is my last comment on the matter.

#479234 (comment)

jopejoe1 · 2026-02-22T15:09:24Z

The 2 options added here match the previous default values of x: {} used in:

nixpkgs/pkgs/development/interpreters/perl/interpreter.nix

Line 24 in 0b721ad

    
           overrides ? config.perlPackageOverrides or (p: { }), # TODO: (self: super: {}) like in python

and

nixpkgs/pkgs/top-level/stage.nix

Line 221 in 0b721ad

    
           lib.optionalAttrs allowCustomOverrides ((config.packageOverrides or (super: { })) super);

If there are anyother usages of thees options they are missusing this config option.

dwt · 2026-02-23T12:42:51Z

@philiptaron @jopejoe1: do I get this right that options like nixpkgs.config.perlPackageOverrides or (p: {}) would be affected, and that this should be a non issue, because the default now becomes part of nixpkgs.config?

If that is all I'm inclined to vote merge. I'm not approving this pull request yet, as I really do not feel that I understand the internals of nixpkgs well enough to confidently make that vote. (sorry @jopejoe1)

philiptaron · 2026-02-23T13:47:13Z

I'm only not merging since I can't monitor for regressions. I think from a conceptual standpoint this is good to go. At worst we will roll it back having learned something and can refer back to it.

dwt

Approving to see what this will break, as I think this is the right direction to go for nixpkgs

nixos-discourse · 2026-02-23T13:55:17Z

This pull request has been mentioned on NixOS Discourse. There might be relevant details there:

https://discourse.nixos.org/t/prs-already-reviewed/2617/2824

roberth

This doubles the module evaluation, leading to double the type checking, even in packageOverrides etc calls, as well as those unfree / insecure predicate functions.

I would prefer to let Nixpkgs to the module evaluation, by forwarding the definitions and putting apply = _nativeMergeIgnored: pkgs.config; in the option.
That way we have better a better separation of concerns, and the types are only applied once, which might matter in some corner cases.

The Nixpkgs function doesn't support accepting raw options.config.definitionsWithLocations (or similar) definitions yet.
So that would have to be added. I'd have to look into the exact details; maybe the new mkDefinition is also helpful.

roberth · 2026-02-24T15:07:37Z

pkgs/top-level/config.nix

+}@args:

 let
+  docPrefix = args.docPrefix or "";


You can't do . or or ? on module arguments directly, because they're generated from the individual module's functionArgs. (otherwise a { ... }: function is by definition strict, ie not lazy like it needs to be)
This should work though:

Suggested change

docPrefix = args.docPrefix or "";

docPrefix = config._module.args.docPrefix or "";

dwt · 2026-02-26T08:45:05Z

@roberth Would you mind explaining a little bit more why this would lead to a double nixpkgs module evaluation? Do you mean of just this module, or of all modules? (Sorry for being the noob in the room)

config.nix: document packageOverrides and perlPackageOverrides

0082b35

These are handled in the NixOS modules for `nixpkgs.config` as special merges; add them here.

jopejoe1 force-pushed the nixpkgs-config branch from 8bf94f4 to 36c82f3 Compare February 12, 2026 19:21

jopejoe1 marked this pull request as draft February 12, 2026 19:22

jopejoe1 force-pushed the nixpkgs-config branch from 36c82f3 to f707c6d Compare February 12, 2026 20:02

jopejoe1 added 2 commits February 12, 2026 21:15

config.nix: add optional docPrefix

21d282b

Makes it possible to render it in the NixOS manual, as that one does not contain the Nixpkgs manual specific ones.

nixos/nixpkgs.config: make use of the module defined in config.nix

d8d2005

This makes it so that the `nixpkgs.config` options can be merged with the module system It also makes the defined options show up in search and the manual.

jopejoe1 force-pushed the nixpkgs-config branch from f707c6d to d8d2005 Compare February 12, 2026 20:15

jopejoe1 marked this pull request as ready for review February 12, 2026 20:31

nixpkgs-ci bot added the 9.needs: reviewer This PR currently has no reviewers requested and needs attention. label Feb 12, 2026

jopejoe1 requested review from infinisil and wolfgangwalther February 12, 2026 21:00

nixpkgs-ci bot removed the 9.needs: reviewer This PR currently has no reviewers requested and needs attention. label Feb 12, 2026

This was referenced Feb 13, 2026

nixos/nixpkgs: merge lists inside config #368051

Open

nixpkgs.config option having unintuitive merging semantic #468647

Open

nixos/misc/nixpkgs add setting nixpkgs.config.allowUnfreePackages = ["list" "of" "packages"] #396595

Merged

jopejoe1 commented Feb 13, 2026

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wolfgangwalther removed their request for review February 13, 2026 13:20

dwt self-requested a review February 14, 2026 08:38

dwt requested a review from roberth February 17, 2026 17:22

jopejoe1 requested a review from philiptaron February 19, 2026 13:47

philiptaron approved these changes Feb 21, 2026

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nixpkgs-ci bot added the 12.approvals: 1 This PR was reviewed and approved by one person. label Feb 21, 2026

dwt approved these changes Feb 23, 2026

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nixpkgs-ci bot added 12.approvals: 2 This PR was reviewed and approved by two persons. and removed 12.approvals: 1 This PR was reviewed and approved by one person. labels Feb 23, 2026

roberth requested changes Feb 24, 2026

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nixpkgs-ci bot added the 2.status: merge conflict This PR has merge conflicts with the target branch label Feb 24, 2026

	docPrefix = args.docPrefix or "";
	docPrefix = config._module.args.docPrefix or "";

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