packageExtra creating requirement conflict with itself

[TyberiusPrime]

{
  inputs = {
    nixpkgs.url = "github:NixOS/nixpkgs/nixos-21.05";
    mach-nix = {
      url = "github:DavHau/mach-nix?rev=51caf584f26acdfaa51bbf7ee1ffa365aea7bc64";
      inputs.nixpkgs.follows = "nixpkgs";
    };
  };

  outputs = flakes @ {
    self,
    nixpkgs,
    mach-nix,
  }: let
    pkgs = import nixpkgs {
      system = "x86_64-linux";
    };
    mach-nix_ = mach-nix.lib."x86_64-linux";

  in {
    defaultPackage.x86_64-linux = mach-nix_.mkPython {
      requirements = ''pandas'';
      packagesExtra = [
        (mach-nix_.buildPythonPackage {
          src = pkgs.fetchgit {
            "rev" = "6c82cdc20d6f81c96772da73fc07a672a0a0a6ef";
            "sha256" = "sha256-ORA+GtORqBDhQiwtXUzooqQXostPrQhwHnlD5sW0kTE=";
            "url" = "https://github.com/has2k1/plotnine";
          };        })      ];    };  };}

leads to

> Mach-nix version: master
       > Python: 3.8.11
       > Cause: Requirements conflict: plotnine
       > The requirements which caused the error:
       >   plotnine

This is, of course, the stripped down example.

Could've sworn this was working a while ago, but the older relases die in a different way (something about an empty file_path).

Am I holding it wrong?

[TyberiusPrime]

ok, the file path issue is #403

[TyberiusPrime]

fun fact, adding a version="123" to buildPytohnPackage makes it build.
It possibly has something to do with the wonky 'derive version from VCS' that plotnine uses.

bonus fun fact:
version="6c82cdc20d6f81c96772da73fc07a672a0a0a6ef" does not work.
version=".6c82cdc" does not work.
version=".6c82c" does not work.
version=".6c82" does work (so it's not 'there is a char present").
version="6c82c" does work.
version="6c82cd" does not work.
version="0123456" does work (so it's not the length)
version="a012345" fails
version="012345a" works.

something is not treating the version string as something opaque.

ok, so it evaluates to "6c82cdc" if you don't set a version.

So why does this then explode downstream?

[TyberiusPrime]

More debugging shows that in resolver/resolvelib_resolver.py ... resolve() around line 66, self.nixpkgs is slightly different
with working and non working versions.
working:
< 'plotnine': {<Version('123')>: ['plotnine']}
non working:

'plotnine': {<LegacyVersion('6c82cdc')>: ['plotnine']}

so that's the next rabbit hole.

[TyberiusPrime]

Got it down to
requirements.py:202

if not req.specs:
        # We filter version with an empty specifier set, since that will filter
        # out prerelease, if there are any other releases.
        return SpecifierSet().filter(versions)

which filters out the one and only available version here.

(which it shouldn't according to the packaging doc's)

[TyberiusPrime]

oh great, LegacyVersion is also going to disappear: pypa/packaging#321

[TyberiusPrime]

once the PR is accepted, this can go away.