"AttributeError: cython_sources" with Cython 3.0.0a10

When attempting to install PyYAML from sources with Cython 3.0.0a10, e.g. like so:

pip install --pre -v git+https://github.com/yaml/pyyaml.git

the install fails with:

Using pip 21.3.1 from /home/florian/tmp/toxtest/.venv/lib/python3.10/site-packages/pip (python 3.10)
Collecting git+https://github.com/yaml/pyyaml.git
  Cloning https://github.com/yaml/pyyaml.git to /tmp/pip-req-build-rdv2sw86
  Running command git version
  git version 2.34.1
  Running command git clone --filter=blob:none -q https://github.com/yaml/pyyaml.git /tmp/pip-req-build-rdv2sw86
  Running command git rev-parse HEAD
  8cdff2c80573b8be8e8ad28929264a913a63aa33
  Resolved https://github.com/yaml/pyyaml.git to commit 8cdff2c80573b8be8e8ad28929264a913a63aa33
  Running command /home/florian/tmp/toxtest/.venv/bin/python3 /tmp/pip-standalone-pip-7sp3xayz/__env_pip__.zip/pip install --ignore-installed --no-user --prefix /tmp/pip-build-env-az2k859x/overlay --no-warn-script-location --no-binary :none: --only-binary :none: -i https://pypi.org/simple --pre -- setuptools wheel Cython
  Collecting setuptools
    Using cached setuptools-60.5.0-py3-none-any.whl (958 kB)
  Collecting wheel
    Using cached wheel-0.37.1-py2.py3-none-any.whl (35 kB)
  Collecting Cython
    Using cached Cython-3.0.0a10-cp310-cp310-manylinux_2_17_x86_64.manylinux2014_x86_64.manylinux_2_24_x86_64.whl (2.2 MB)
  Installing collected packages: wheel, setuptools, Cython
  Successfully installed Cython-3.0.0a10 setuptools-60.5.0 wheel-0.37.1
  Installing build dependencies ... done
  Running command /home/florian/tmp/toxtest/.venv/bin/python3 /home/florian/tmp/toxtest/.venv/lib/python3.10/site-packages/pip/_vendor/pep517/in_process/_in_process.py get_requires_for_build_wheel /tmp/tmpqirb9t5l
  running egg_info
  creating lib/PyYAML.egg-info
  writing manifest file 'lib/PyYAML.egg-info/SOURCES.txt'
  Traceback (most recent call last):
    File "/home/florian/tmp/toxtest/.venv/lib/python3.10/site-packages/pip/_vendor/pep517/in_process/_in_process.py", line 363, in <module>
      main()
    File "/home/florian/tmp/toxtest/.venv/lib/python3.10/site-packages/pip/_vendor/pep517/in_process/_in_process.py", line 345, in main
      json_out['return_val'] = hook(**hook_input['kwargs'])
    File "/home/florian/tmp/toxtest/.venv/lib/python3.10/site-packages/pip/_vendor/pep517/in_process/_in_process.py", line 130, in get_requires_for_build_wheel
      return hook(config_settings)
    File "/tmp/pip-build-env-az2k859x/overlay/lib/python3.10/site-packages/setuptools/build_meta.py", line 162, in get_requires_for_build_wheel
      return self._get_build_requires(
    File "/tmp/pip-build-env-az2k859x/overlay/lib/python3.10/site-packages/setuptools/build_meta.py", line 143, in _get_build_requires
      self.run_setup()
    File "/tmp/pip-build-env-az2k859x/overlay/lib/python3.10/site-packages/setuptools/build_meta.py", line 158, in run_setup
      exec(compile(code, __file__, 'exec'), locals())
    File "setup.py", line 288, in <module>
      setup(
    File "/tmp/pip-build-env-az2k859x/overlay/lib/python3.10/site-packages/setuptools/__init__.py", line 155, in setup
      return distutils.core.setup(**attrs)
    File "/tmp/pip-build-env-az2k859x/overlay/lib/python3.10/site-packages/setuptools/_distutils/core.py", line 148, in setup
      return run_commands(dist)
    File "/tmp/pip-build-env-az2k859x/overlay/lib/python3.10/site-packages/setuptools/_distutils/core.py", line 163, in run_commands
      dist.run_commands()
    File "/tmp/pip-build-env-az2k859x/overlay/lib/python3.10/site-packages/setuptools/_distutils/dist.py", line 967, in run_commands
      self.run_command(cmd)
    File "/tmp/pip-build-env-az2k859x/overlay/lib/python3.10/site-packages/setuptools/_distutils/dist.py", line 986, in run_command
      cmd_obj.run()
    File "/tmp/pip-build-env-az2k859x/overlay/lib/python3.10/site-packages/setuptools/command/egg_info.py", line 299, in run
      self.find_sources()
    File "/tmp/pip-build-env-az2k859x/overlay/lib/python3.10/site-packages/setuptools/command/egg_info.py", line 306, in find_sources
      mm.run()
    File "/tmp/pip-build-env-az2k859x/overlay/lib/python3.10/site-packages/setuptools/command/egg_info.py", line 541, in run
      self.add_defaults()
    File "/tmp/pip-build-env-az2k859x/overlay/lib/python3.10/site-packages/setuptools/command/egg_info.py", line 578, in add_defaults
      sdist.add_defaults(self)
    File "/tmp/pip-build-env-az2k859x/overlay/lib/python3.10/site-packages/setuptools/_distutils/command/sdist.py", line 228, in add_defaults
      self._add_defaults_ext()
    File "/tmp/pip-build-env-az2k859x/overlay/lib/python3.10/site-packages/setuptools/_distutils/command/sdist.py", line 312, in _add_defaults_ext
      self.filelist.extend(build_ext.get_source_files())
    File "setup.py", line 204, in get_source_files
      self.cython_sources(ext.sources, ext)
    File "/tmp/pip-build-env-az2k859x/overlay/lib/python3.10/site-packages/setuptools/_distutils/cmd.py", line 103, in __getattr__
      raise AttributeError(attr)
  AttributeError: cython_sources
  Getting requirements to build wheel ... error
WARNING: Discarding git+https://github.com/yaml/pyyaml.git. Command errored out with exit status 1: /home/florian/tmp/toxtest/.venv/bin/python3 /home/florian/tmp/toxtest/.venv/lib/python3.10/site-packages/pip/_vendor/pep517/in_process/_in_process.py get_requires_for_build_wheel /tmp/tmpqirb9t5l Check the logs for full command output.
ERROR: Command errored out with exit status 1: /home/florian/tmp/toxtest/.venv/bin/python3 /home/florian/tmp/toxtest/.venv/lib/python3.10/site-packages/pip/_vendor/pep517/in_process/_in_process.py get_requires_for_build_wheel /tmp/tmpqirb9t5l Check the logs for full command output.

I’m not sure if this is an intended change in Cython 3, or a bug - but given that “pyyaml setup is still relying on a bunch of ancient custom distutils bits” (#584) I thought I’d report it here first. Please let me know if you think I should rather report it there.

[nitzmahone]

It’s definitely a regression between Cython 3.0.0a9 and a10; every previous 3.0.0 alpha has been able to build the pyyaml extension fine. This PR (included in a10) swapped out the base class on Cython’s custom build_ext distutils command (which pyyaml further subclasses to customize some stuff). I haven’t dug down all the way yet to see if it’s something we should try to address in pyyaml’s customization or if it’s just a bug in the new base class.

Thanks for the report- regardless, we’ll want to get this sorted one way or another, so I’ll figure out where the problem is and work with the Cython/setuptools folks if necessary to get it working.

[nitzmahone]

Yep, unfortunately --pre seems to affect all deps and build deps as well under pip.