How to set up build system override in `mkPoetryEnv`?

[l0b0]

Describe the issue

As a relative Nix newbie it's not obvious how to create a new override to emulate addBuildSystem (I'm trying to avoid changing build-systems.json itself, if that makes sense). For example, jsonschema 4.6.0 seems to require hatchling, but the override

jsonschema = super.jsonschema.overridePythonAttrs (
  old: {
    nativeBuildInputs = (old.nativeBuildInputs or [ ]) ++ [
      self.hatchling
      self.hatch-vcs
    ];
  }
);

just results in a different error:

ERROR: Could not find a version that satisfies the requirement pluggy>=1.0.0; python_version > "3" (from hatchling) (from versions: none)

Does this error require a different override, or did I do something wrong with my hatchling override?

[sigprof]

The above override actually works for me if I use a recent nixpkgs snapshot that has usable hatchling and hatch-vcs Python packages.

Another option is to add the required modules to pyproject.toml (e.g., to the [tool.poetry.dev-dependencies] section), then poetry2nix would use the module versions specified there instead of taking whatever is in nixpkgs (and would also pick up any dependencies like that pluggy module). However, you may run into version conflicts with other modules; e.g., this is what I ended up with at the moment:

# These dependencies are required by the jsonschema >= 4.6.0 build system, but
# are not detected automatically; they are also not present in the used Nixpkgs
# snapshot, so need to be obtained through Poetry.
hatchling = "*"
hatch-vcs = "*"

# The `pytest` module in the used Nixpkgs snapshot has an upper bound on the
# `pluggy` dependency, which conflicts with the dependency of the `hatchling`
# module; upgrading the `pytest` module fixes the conflict.
pytest = "*"

# Building the `tomli` module, which is in the dependency tree of `hatchling`,
# requires a newer `flit-core` module than found in the used Nixpkgs snapshot.
flit-core = "*"

I suppose that the PR to add the override for jsonschema would need to use if (lib.versionAtLeast super.jsonschema.version "4.6.0") to keep older module versions working as before.

[l0b0]

@sigprof I get the same error message when using both the 22.05 stable nixpkgs and today's version:

{ pkgs ? import
    (
      fetchTarball
        {
          name = "nixpkgs-22.05-2022-06-13";
          url = "https://github.com/NixOS/nixpkgs/archive/37b6b161e536fddca54424cf80662bce735bdd1e.tar.gz";
          sha256 = "1zwv5qcz5pnyj1ya7ia6rd5d9i0l40pc8av6blf0065hwd1nh7p1";
        })
    { }
}:
[…]
      jsonschema = super.jsonschema.overridePythonAttrs (
        old: {
          nativeBuildInputs = (old.nativeBuildInputs or [ ]) ++ [
            self.hatchling
            self.hatch-vcs
          ];
        }
      );
[…]

Could you please post your full shell.nix if you got this to work?

In any case, the underlying question is different: How do I set up a build system override in mkPoetryEnv?

[sigprof]

@l0b0 The exact version of the code which works for me is https://github.com/sigprof/nix-devenv-qmk/tree/e9ae48fb368951d3eaa13f2d0d837fc803934557 (beware that it is pinned on a rather old version of nixpkgs and stays on it for now to avoid causing a rebuild of pkgsCross.avr.buildPackages.gcc8 for its users; you can set avr to false to avoid the need to compile that part). Although I also tried to switch nixpkgs to a recent snapshot — in that case the override worked too even without the pyproject.toml change and the corresponding poetry.lock update.

Note that self.hatchling inside the override is actually affected by the content of poetry.lock, so your problem may be actually caused by some conflicts in the package set that you are trying to build, and you may actually need to make some adjustments to your pyproject.toml because of that.

As for the general question of setting up a build system override, from looking at how addBuildSystem is defined and how it is then used when processing build-systems.json it looks like the only thing that your replacement definition is missing is the check for old ? format && old.format == "wheel", which does not seem to be important in this particular case (apparently Poetry wants to rebuild the package instead of using a wheel).