ResolutionImpossible: kappa==0.6.0 on pkgs.python36

let
  mach-nix-src-boot = builtins.fetchGit {
    url = "https://github.com/DavHau/mach-nix/";
    ref = "refs/tags/2.3.0";
  };
  mach-nix-boot = import mach-nix-src-boot;
  pkgs-boot = mach-nix-boot.nixpkgs;
  mach-nix-src = let
    src = mach-nix-src-boot;
    patches = [
      (builtins.toFile "mach-nix-dump.patch" ''
--- a/mach_nix/generate.py
+++ b/mach_nix/generate.py
@@ -1,6 +1,7 @@
 import json
 import os
 import sys
+import traceback
 from os.path import dirname
 from pprint import pformat
 from typing import List
@@ -88,6 +89,7 @@ def handle_resolution_impossible(exc: ResolutionImpossible, reqs_str, providers_
         f"The requirements which caused the error:"
         f"{causes_str}\n",
         file=sys.stderr)
+    traceback.print_exc(file=sys.stderr)
 
 
 if __name__ == "__main__":
      '')
    ];
  in if patches == [ ] then src else pkgs-boot.applyPatches {
    name = "match-nix-src-patched";
    inherit src patches;
  };
  mach-nix = import mach-nix-src;
  pkgs = mach-nix.nixpkgs;
  machNixFile-src = "${mach-nix-src}/mach_nix/nix/mach.nix";
  machNixFile = import machNixFile-src;
in machNixFile {
  python = pkgs.python36; # failure
  # python = pkgs.python37; # success
  requirements = ''
    kappa==0.6.0
  '';
}

bb010g ~/.../python/example-nixpkgs-dev-env % nix-build --show-trace -k mach-nix-mwe.nix
these derivations will be built:
  /nix/store/s2dcbcbfgbqyfps1lh920br4ih5qnzy0-mach_nix_file.drv
building '/nix/store/s2dcbcbfgbqyfps1lh920br4ih5qnzy0-mach_nix_file.drv'...

Some requirements could not be resolved.
Top level requirements:
  kappa==0.6.0
Providers:
  {'_default': 'wheel,sdist,nixpkgs',
   'gdal': 'nixpkgs',
   'pip': 'nixpkgs',
   'setupmeta': 'wheel',
   'setuptools': 'nixpkgs',
   'wheel': 'nixpkgs,sdist'}
Mach-nix version: 2.3.0
Python: 3.6.11
Cause: Requirements conflict: Requirement.parse('kappa==0.6.0')
The requirements which caused the error:
  kappa==0.6.0

Traceback (most recent call last):
  File "/nix/store/h7sh37qqjhyw7bp55csg88yic3ymvk82-python3-3.7.8-env/lib/python3.7/site-packages/resolvelib/resolvers.py", line 185, in
 _merge_into_criterion
    crit = self.state.criteria[name]
KeyError: 'kappa'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/nix/store/h7sh37qqjhyw7bp55csg88yic3ymvk82-python3-3.7.8-env/lib/python3.7/site-packages/resolvelib/resolvers.py", line 280, in
 resolve
    name, crit = self._merge_into_criterion(r, parent=None)
  File "/nix/store/h7sh37qqjhyw7bp55csg88yic3ymvk82-python3-3.7.8-env/lib/python3.7/site-packages/resolvelib/resolvers.py", line 187, in
 _merge_into_criterion
    crit = Criterion.from_requirement(self._p, requirement, parent)
  File "/nix/store/h7sh37qqjhyw7bp55csg88yic3ymvk82-python3-3.7.8-env/lib/python3.7/site-packages/resolvelib/resolvers.py", line 87, in
from_requirement
    raise RequirementsConflicted(criterion)
resolvelib.resolvers.RequirementsConflicted: Requirements conflict: Requirement.parse('kappa==0.6.0')

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/nix/store/5daxyvrpm6b3l3s8ag1cf9wysifzaciw-yky9dfn076mgcc359aaj46b7vz0i3xv7-match-nix-src-patched/mach_nix/generate.py", line 6
4, in main
    expr = generator.generate(reqs)
  File "/nix/store/5daxyvrpm6b3l3s8ag1cf9wysifzaciw-yky9dfn076mgcc359aaj46b7vz0i3xv7-match-nix-src-patched/mach_nix/generators/overides_
generator.py", line 34, in generate
    pkgs = self.resolver.resolve(reqs)
  File "/nix/store/5daxyvrpm6b3l3s8ag1cf9wysifzaciw-yky9dfn076mgcc359aaj46b7vz0i3xv7-match-nix-src-patched/mach_nix/resolver/resolvelib_
resolver.py", line 63, in resolve
    result = resolvelib.Resolver(Provider(self.nixpkgs, self.deps_provider), reporter).resolve(reqs, max_rounds=1000)
  File "/nix/store/h7sh37qqjhyw7bp55csg88yic3ymvk82-python3-3.7.8-env/lib/python3.7/site-packages/resolvelib/resolvers.py", line 413, in
 resolve
    state = resolution.resolve(requirements, max_rounds=max_rounds)
  File "/nix/store/h7sh37qqjhyw7bp55csg88yic3ymvk82-python3-3.7.8-env/lib/python3.7/site-packages/resolvelib/resolvers.py", line 282, in
 resolve
    raise ResolutionImpossible(e.criterion.information)
resolvelib.resolvers.ResolutionImpossible: [RequirementInformation(requirement=Requirement.parse('kappa==0.6.0'), parent=None)]
builder for '/nix/store/s2dcbcbfgbqyfps1lh920br4ih5qnzy0-mach_nix_file.drv' failed with exit code 1
error: build of '/nix/store/s2dcbcbfgbqyfps1lh920br4ih5qnzy0-mach_nix_file.drv' failed
(100) bb010g ~/.../python/example-nixpkgs-dev-env %

Chasing stacktraces around hasn’t really gone anywhere. If you let the requirement float (kappa), kappa==0.3.1 is picked. A requirement of kappa>0.3.1 fails.

[DavHau]

With this fix and a few other improvements I just added, you can build kappa now like this:

let
  mach-nix = import (builtins.fetchGit {
    url = "https://github.com/DavHau/mach-nix/";
    rev = "469891f8d0959aa97b3a0e3566a70488caeac499";
  });
  kappa = mach-nix.buildPythonPackage (mach-nix.fetchPypiSdist "kappa" "0.6.0");
in
kappa

[DavHau]

I added the missing variable to the crawler and deleted ~ 188K DB entries which had the same error. It might take a few days for the crawler to re-crawl those releases.