remove cases where cabal2nix produces a stringy license by jopejoe1 · Pull Request #677 · NixOS/cabal2nix

jopejoe1 · 2025-10-18T22:41:44Z

I'm working on removing all stringy licenses in nixpkgs, and currently the only ones left are the ones in haskellPackages ~~and node2nix packages~~. This change fixes the ones for Haskell packages.

sternenseemann

Please also add a changelog entry, ideally noting when nixpkgs added support for lib.licensesSpdx.

sternenseemann · 2025-10-18T22:54:02Z


 fromCabalLicense :: Distribution.License.License -> Distribution.Nixpkgs.License.License
-fromCabalLicense (GPL Nothing)                             = Unknown (Just "GPL")
+fromCabalLicense (GPL Nothing)                             = Known "lib.licenses.gpl2Plus"


These cases are intentional as there is not enough information to conclude what variant of the license in question is used.

I do realize they were intentional, but they can't stay in their current form. I'm currently working towards disallowing stringy licenses in nixpkgs, and those are pretty much the only ones left. Other options would be to make it even less informational with lib.licenses.free or to add a new custom license (not really a fan of this).

I looked at a few packages in more detail and I think we can reasonably do two things:

interpret GPL as gpl2Plus as done here. That's because they could have used GPL-2 or GPL-3 if they wanted to be more specific.

just use free as fallback for this.

For me, both are fine.

free as a fallback seems reasonable for GPL without further specification, that is a good idea. (But not in general as a fallback for unknown, see #677 (comment)).

wolfgangwalther · 2025-10-23T09:49:54Z

  homepage = "https://github.com/blamario/incremental-parser";
  description = "Generic parser library capable of providing partial results from partial input";
-  license = "GPL";
+  license = lib.licenses.gpl2Plus;


Upstream has changed to GPL-3 by now.

It is probably fine to update these test expressions to newer versions of the cabal file, but some of them may test something specific that has since been removed.

wolfgangwalther · 2025-10-23T09:51:56Z

  homepage = "http://github.com/jgm/highlighting-kate";
  description = "Syntax highlighting";
-  license = "GPL";
+  license = lib.licenses.gpl2Plus;


Upstream still uses GPL, and has gpl2Only, I think: https://github.com/jgm/highlighting-kate/blob/master/LICENSE

wolfgangwalther · 2025-10-23T09:57:02Z

  homepage = "https://github.com/skogsbaer/HTF/";
  description = "The Haskell Test Framework";
-  license = "LGPL";
+  license = lib.licenses.lgpl2Plus;


Upstream has now LGPL-2.1, which renders as LGPL-2.1-only on hackage.

wolfgangwalther · 2025-10-23T10:00:34Z

  homepage = "https://wiki.haskell.org/Lambdabot";
  description = "Social plugins for Lambdabot";
-  license = "GPL";
+  license = lib.licenses.gpl2Plus;


lambdabot-social-plugins has GPL, but.. the license looks like BSD/MIT: https://github.com/lambdabot/lambdabot/blob/master/lambdabot-social-plugins/LICENSE

wolfgangwalther · 2025-10-23T10:02:42Z

  homepage = "http://github.com/jgm/texmath";
  description = "Conversion between formats used to represent mathematics";
-  license = "GPL";
+  license = lib.licenses.gpl2Plus;


texmath has updated to GPL-2, which renders as GPL-2.0-only on hackage.

wolfgangwalther · 2025-10-23T10:05:07Z


 fromCabalLicense :: Distribution.License.License -> Distribution.Nixpkgs.License.License
-fromCabalLicense (GPL Nothing)                             = Unknown (Just "GPL")
+fromCabalLicense (GPL Nothing)                             = Known "lib.licenses.gpl2Plus"


I looked at a few packages in more detail and I think we can reasonably do two things:

interpret GPL as gpl2Plus as done here. That's because they could have used GPL-2 or GPL-3 if they wanted to be more specific.

just use free as fallback for this.

For me, both are fine.

sternenseemann · 2025-10-24T19:30:51Z

For context, see also #520.

One thing to keep in mind is that while cabal2nix mostly deals with Hackage, it may also process arbitrary cabal files. We can make some assumptions in Nixpkgs since additions of unfree packages would always have to be manual, but it does not seem wise to have such assumptions leak into cabal2nix which may be used in arbitrary ways on arbitrary inputs.

In particular,

I don't like mapping ambiguous licenses to something we reckon is probably right. If we don't have enough information to accurately determine the license from metadata, we should not guess. Instead, such information needs to be set manually via overrides in Nixpkgs. This gets the desired effect (no stringy licenses) without requiring questionable behavior. Also, it creates an incentive to get upstream maintainers to update their meta data. (Edit: Mapping GPL to free as suggested in remove cases where cabal2nix produces a stringy license #677 (comment) is correct, so we could do that.)
We also should not map anything to lib.licenses.free because it only holds for Hackage packages. cabal2nix can't tell a package descriptions origin in all cases, so this is an exercise in futility. If license information is missing, I would propose we just do not set license and change haskellPackages.mkDerivation to allow for this.

Apologies for the inconsistent messages. Some of my earlier comments were informed by an incorrect assumption how we decide on free/nonfree.

(Note that prior to #520, cabal2nix would prevent “unfree” packages from being built on Hydra, but Nixpkgs seems to consider stringy licenses as free by default (?). So from cabal2nix's perspective, we are currently always reporting the license accurately without any illegitimate transformations and letting Nixpkgs decide whether it is free or unfree. This should be preserved, in my opinion.)

sternenseemann · 2025-10-24T21:03:37Z

Cherry picked 7a5af01 onto master.

sternenseemann · 2025-10-26T11:21:44Z

We currently have about 250 packages with a string license we actually are building and distributing. In total, haskellPackages contains about 1000 packages with a stringy license, about 75% of those are currently marked as broken or depend on a broken dependency.

`stdenv.mkDerivation` does not require meta.license to be passed, so there is no reason `haskellPackages.mkDerivation` needs to enforce this. This would free up cabal2nix to not report a license if it is not sure. As I have argued in NixOS/cabal2nix#677 (comment), it is better not to report a license than reporting an inaccurate one. This would also allow to stop generating arbitrary strings as licenses in cabal2nix to remove string values to facilitate more cleanliness in the spirit of #445672, though the question is whether it is wise to remove the meta data altogether.

jopejoe1 · 2025-12-06T10:44:07Z

Sorry for not being really active in here was working on an improvement for licenses in nixpkgs for making this nicer to implement here. see NixOS/nixpkgs#468378

jopejoe1 · 2026-04-20T11:05:18Z

Did a larger refactor based on the changes done in NixOS/nixpkgs#468378 and the feedback that was given here.

jopejoe1 · 2026-07-06T06:29:13Z

Now that compound licenses are supported in all supported nixpkgs versions, could this be moved forward?

sternenseemann · 2026-07-06T08:28:17Z

Yes, I'd be interested in that!

Though, I'm still of the position that we should not fall back to something nondescript like licenses.free if we don't recognize the license. That can be solved manually in Nixpkgs or upstream (ideally). Probably a lot of packages affected by this would also wind up excluded eventually.

make use of the new compaund licenses in nixpkgs to get more correct licensing information

we do our own logic in nixpkgs based on is writen in meta.licenses with more complex logic than this

if we don't know the specific version of a license fallback to a generic free license

jopejoe1 · 2026-07-11T12:50:29Z

Should work like this now.

sternenseemann requested changes Oct 18, 2025

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jopejoe1 force-pushed the licenses branch from c3b971c to 1a2e97e Compare October 19, 2025 00:09

wolfgangwalther reviewed Oct 23, 2025

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sternenseemann reviewed Oct 24, 2025

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Comment thread cabal2nix/src/Distribution/Nixpkgs/Haskell/FromCabal/License.hs Outdated

Comment thread cabal2nix/src/Distribution/Nixpkgs/Haskell/FromCabal/License.hs Outdated

Comment thread cabal2nix/src/Distribution/Nixpkgs/Haskell/FromCabal/License.hs Outdated

sternenseemann mentioned this pull request Oct 26, 2025

haskellPackages.mkDerivation: make license optional NixOS/nixpkgs#455796

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jopejoe1 mentioned this pull request Dec 16, 2025

Packages with meta.license as string are always considered as free NixOS/nixpkgs#269788

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jopejoe1 marked this pull request as draft January 14, 2026 10:18

jopejoe1 force-pushed the licenses branch 3 times, most recently from 002da57 to 02b5459 Compare April 20, 2026 11:01

jopejoe1 changed the title ~~make parsed license to be less like tobe a stringy license~~ reduce the cases where cabal2nix produces a stringy license Apr 20, 2026

jopejoe1 marked this pull request as ready for review April 20, 2026 11:03

jopejoe1 mentioned this pull request Apr 20, 2026

lib.licenses: add universalFOSSException-10 NixOS/nixpkgs#511720

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jopejoe1 requested a review from sternenseemann April 20, 2026 12:57

jopejoe1 force-pushed the licenses branch from 02b5459 to 31ebb7d Compare April 23, 2026 06:56

jopejoe1 changed the title ~~reduce the cases where cabal2nix produces a stringy license~~ remove cases where cabal2nix produces a stringy license Apr 23, 2026

jopejoe1 added 6 commits July 11, 2026 14:25

fromSPDXLicense: handle compound licenses

0127bd8

make use of the new compaund licenses in nixpkgs to get more correct licensing information

fromCabal: don't set hydra platfrom depending on license

149ba90

we do our own logic in nixpkgs based on is writen in meta.licenses with more complex logic than this

fromCabalLicense: return non specific varints as generic free

54c0c43

if we don't know the specific version of a license fallback to a generic free license

fromCabalLicense: don't set any license as fallback

ee6ee85

fromCabalLicense: use compound license

e8e823e

cabal2nix: add info about license changes to changelog

b648657

jopejoe1 force-pushed the licenses branch from 31ebb7d to b648657 Compare July 11, 2026 12:49

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