Falling back to setuptools.build_meta:__legacy__ is the standard behavior,
not setuptools.build_meta. See PEP 517:
https://www.python.org/dev/peps/pep-0517/
> If the pyproject.toml file is absent, or the build-backend key is missing,
> the source tree is not using this specification, and tools should revert
> to the legacy behaviour of running setup.py (either directly, or by
> implicitly invoking the setuptools.build_meta:__legacy__ backend).
Falling back to setuptools.build_meta had very similar results so far.,
but the behavior might change in the feature.
While working on this, I have uncovered a problem in our code.
It was not able to handle backends with ":". Looking at PEP 517 again:
> build-backend is a string naming a Python object that will be used to
> perform the build. This is formatted following the same module:object syntax
> as a setuptools entry point. For instance, if the string is "flit.api:main",
> this object would be looked up by executing the equivalent of:
>
> import flit.api
> backend = flit.api.main
>
> It's also legal to leave out the :object part, e.g.
>
> build-backend = "flit.api"
>
> which acts like:
>
> import flit.api
> backend = flit.api
We now handle such cases properly. Witch the change of the default backend,
we also test a backend with colon in our tests.
Previously, it wasn't possible to see why tox failed:
...
Requirement satisfied: tox-current-env >= 0.0.2
(installed: tox-current-env 0.0.2)
Traceback (most recent call last):
File "/usr/lib/rpm/redhat/pyproject_buildrequires.py", line 269, in main
generate_requires(
File "/usr/lib/rpm/redhat/pyproject_buildrequires.py", line 221, in generate_requires
generate_tox_requirements(toxenv, requirements)
File "/usr/lib/rpm/redhat/pyproject_buildrequires.py", line 184, in generate_tox_requirements
r = subprocess.run(
File "/usr/lib64/python3.8/subprocess.py", line 512, in run
raise CalledProcessError(retcode, process.args,
subprocess.CalledProcessError: Command '['tox', '--print-deps-to-file', '/tmp/tmp96smu4rv', '-qre', 'py38']' returned non-zero exit status 1.
Now it is:
...
Requirement satisfied: tox-current-env >= 0.0.2
(installed: tox-current-env 0.0.2)
ERROR: tox config file (either pyproject.toml, tox.ini, setup.cfg) not found
Traceback (most recent call last):
File "/usr/lib/rpm/redhat/pyproject_buildrequires.py", line 270, in main
generate_requires(
File "/usr/lib/rpm/redhat/pyproject_buildrequires.py", line 222, in generate_requires
generate_tox_requirements(toxenv, requirements)
File "/usr/lib/rpm/redhat/pyproject_buildrequires.py", line 193, in generate_tox_requirements
r.check_returncode()
File "/usr/lib64/python3.8/subprocess.py", line 444, in check_returncode
raise CalledProcessError(self.returncode, self.args, self.stdout,
subprocess.CalledProcessError: Command '['tox', '--print-deps-to-file', '/tmp/tmpwp8sffv1', '-qre', 'py38']' returned non-zero exit status 1.
Inspired by https://src.fedoraproject.org/rpms/python-chaospy/pull-request/1#comment-32750
