uuid package cannot be overrided with Git source

[malteneuss]

I would like to use a fork of the uuid package as suggested in https://community.flake.parts/haskell-flake/dependency#path

inputs = {
   # uuid v7 support
    uuid-repo.url = "github:LaurentRDC/uuid/594487ca4d606f767833f390714195eedcd2886e";
    uuid-repo.flake = false; 
...

   packages.uuid.source =  "${inputs.uuid-repo}/uuid";

But that fork uses the same version number as in the base packages and there uses the hash of that base pacakage, which doesn't fit:

error: hash mismatch in fixed-output derivation '/nix/store/b4b4bfd3b8jbychnw0p68qyc3inyz1pn-uuid-1.3.16-r1.cabal.drv':
         specified: sha256-JicgiD0dTsUZap8e/jq1N064cVkrSt1QsquIEmL5H3E=
            got:    sha256-DjFOT5Z8TV66pOw/mTaCjgf5Qg5HAgOEQaJx/0Iieek=
error: 1 dependencies of derivation '/nix/store/qm1v419qbicxfdnj8mwxqhlpvz2vn5sn-uuid-1.3.16.drv' failed to build

How can i override the hash? I can't find any attribute in e.g. https://github.com/srid/haskell-flake/blob/master/nix/modules/project/settings/all.nix. Maybe this custom can be used somehow?

fyi:
i tried applying a patch that changes the version number in the projects uuid.cabal file but that didn't work:

    ...settings.uuid.patches = [ ./uuid-version-bump.patch ];

The patch seems to be applied too late for the version number extraction.

Creating a fork with the version number changed to 1.3.17 goes a bit further, but fails later with

error: builder for '/nix/store/nm120iy3nnlnjdlifx16nsj49ifv2ikx-uuid-1.3.17-r1.cabal.drv' failed with exit code 1;
       last 19 log lines:
       >
       > trying https://hackage.haskell.org/package/uuid-1.3.17/revision/1.cabal
       >   % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
       >                                  Dload  Upload   Total   Spent    Left  Speed
       >   0     0    0     0    0     0      0      0 --:--:-- --:--:-- --:--:--     0
       > curl: (22) The requested URL returned error: 404

It still apparently tries to get revision information from Hackage.

[srid]

hash of a Haskell package

You lost me there. What is this hash you are referring to? (I don't think you are referring to the flake input's hash)

Make sure that you override all 3 packages: uuid, uuid-types and uuid-bench.

uses the same version number as in the base packages

This is strange too.

i tried applying a patch that changes the version number

This is like applying a bandaid that doesn't address the root issue, no?

Is it just the uuid package that behaves strangely? If so, is nixpkgs doing something unique here? I would investigate this a bit, @malteneuss

[malteneuss]

Thanks for the quick response.

I tried adding all the other subpackages uuid-types and uuid-bench, but that doesn't make a difference. The mentioned hash is likely the hash of the cabal file that nixpkgs(?) is apparently trying to download under the hood to get the latest revision(?) of a package.

Could it be that with Haskell-flake just overriding package.<name>.source with a raw Git project is missing to override in nixpkgs that Hackage should not be checked? A Git project may not exist on Hackage after all. Although i couldn't find any flag or similar. Do you know of such a setting? You certainly have a better overview of the nixpkgs Haskell code.

edit: I figured out that the default base package uuid has indeed a "revision" attribute (and a edited cabal file hash) that other base packages don't have:

"uuid" = callPackage
    ({ mkDerivation, base, binary, bytestring, cryptohash-md5
     , cryptohash-sha1, entropy, network-info, QuickCheck, random, tasty
     , tasty-hunit, tasty-quickcheck, text, time, uuid-types
     }:
     mkDerivation {
       pname = "uuid";
       version = "1.3.15";
       sha256 = "0r05h16gd7fgfpq9iz43jcn9jzrgfa0gk4cv1xy0p4rli66rb1gq";
       revision = "3";
       editedCabalFile = "089q2i4rmw8iqzjn2fif4yarnbb7gsnsa4c4zhl24l2hlyakymbx";
       libraryHaskellDepends = [
         base binary bytestring cryptohash-md5 cryptohash-sha1 entropy
         network-info random text time uuid-types
       ];
       testHaskellDepends = [
         base bytestring QuickCheck random tasty tasty-hunit
         tasty-quickcheck
       ];
       description = "For creating, comparing, parsing and printing Universally Unique Identifiers";
       license = lib.licenses.bsd3;
     }) {};

  "uuid_1_3_16" = callPackage
    ({ mkDerivation, base, binary, bytestring, cryptohash-md5
     , cryptohash-sha1, entropy, network-info, QuickCheck, random, tasty
     , tasty-hunit, tasty-quickcheck, text, time, uuid-types
     }:
     mkDerivation {
       pname = "uuid";
       version = "1.3.16";
       sha256 = "1xhdf8zw2n2h4c0f8xf76c2gsjvldz34zgc4sn6wqpzcnk7pjihs";
       revision = "1";
       editedCabalFile = "1sbr491gywd2862060j71r1gj1wfh8v9jgzcljx5wkbwjr7lwc8f";
       libraryHaskellDepends = [
         base binary bytestring cryptohash-md5 cryptohash-sha1 entropy
         network-info random text time uuid-types
       ];
       testHaskellDepends = [
         base bytestring QuickCheck random tasty tasty-hunit
         tasty-quickcheck
       ];
       description = "For creating, comparing, parsing and printing Universally Unique Identifiers";
       license = lib.licenses.bsd3;
       hydraPlatforms = lib.platforms.none;
     }) {};

https://raw.githubusercontent.com/NixOS/nixpkgs/refs/heads/nixpkgs-unstable/pkgs/development/haskell-modules/hackage-packages.nix

[srid]

haskell-flake simply provides simpler UX on top of nixpkgs. Understanding how it translates to "low level" nixpkgs code may help in investigating this further. packages.*.source basically gets converted into Haskell overlay. Along with settings.* (another overlay) they get composed on top of basePackages to produce the final package set. First, we merge all overlays:

haskell-flake/nix/modules/project/outputs.nix

Lines 86 to 89 in 94edd6d

	finalOverlay = lib.composeManyExtensions ([
	config.packagesOverlay
	config.settingsOverlay
	] ++ config.otherOverlays);

We then use this final overlay by calling extend on basePackages.

haskell-flake/nix/modules/project/outputs.nix

Line 91 in 94edd6d

finalPackages = config.basePackages.extend finalOverlay;

Perhaps nixpkgs does something special with uuid such that it cannot be extended in this way?

[malteneuss]

I saw in some examples in nixpkgs that you can remove those "revision" and "editedCabalFile" with e.g.

  mbox = appendPatch ./patches/mbox-time-1.10.patch
    (overrideCabal { editedCabalFile = null; revision = null; } super.mbox);

Can we do that through the haskell-flake settings interface somehow? I think then this could be solved. (I could write and create a documentation PR)

[malteneuss]

I think i figured it out:

inputs = {
   # uuid v7 support
    uuid-repo.url = "github:LaurentRDC/uuid/594487ca4d606f767833f390714195eedcd2886e";
    uuid-repo.flake = false; 
...
  {
   packages.uuid.source =  "${inputs.uuid-repo}/uuid";
  # uuid already has a config in nixpkgs with a revision number and a overriden/edited cabal file, which we have to reset:
  settings.uuid.custom =  pkg: pkgs.haskell.lib.compose.overrideCabal (old: { editedCabalFile = null; revision = null; }) pkg;
}