build: respect the "pure" argument at metadata generation time #1417
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When a pure build is requested, no compiled extensions are produced. The setuptools_rust dependency ends up imported-but-not-used. Teach setuptools to avoid build-requiring it in this case. Closes: jelmer#1405
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| else: | ||
| setup_requires = ["setuptools_rust"] | ||
| # We check for egg_info since that indicates we are running prepare_metadata_for_build_* | ||
| if "egg_info" in sys.argv: |
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It is heavily baked into the setuptools design so if it ever did change I would expect it to be extremely long-term... and there are a bunch of packages that work like this already.
@jaraco / @abravalheri could confirm if there's any plans to change it -- but I think it would break far too many projects to be worth changing, especially if no replacement is available for the existing comment:
# Ideally, setuptools would just provide a way to do this
Either setuptools needs to provide a full-fledged API for defining build options, or it needs to allow people to execute build options in setup.py as pure python code hooking into phases such as egg_info and conditionally defining build metadata.
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Setuptools is driving users toward standards-based tooling. Setuptools' PEP 517 implementation passes setup_requires through as get_requires_for_build_*. However, I'd only expect this setting to have effect when building the sdist or the wheel. I'd not expect it to occur when running egg-info.
Regardless, Setuptools has deprecated use of setup.py invocations, so if this behavior is needed, I'd work to investigate alternative reasons to support setup.py egg_info.
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We aren't invoking setup.py here, the expected use of dulwich is to run python -m build and as of today, this PR works fine.
When python -m build runs the official get_requires_for_build_* hook provided by setuptools.build_meta, setuptools internally runs egg_info, that is why we check sys.argv -- because we only want to import the setuptools_rust package that is used for defining Rust extensions, when running build_wheel, not when running get_requires_for_* (setup.py will error out if the dependencies aren't installed).
It is necessary because setup.py is being used to execute code as part of setuptools.build_meta -- no one is running python setup.py .... at any point.
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I'd be interested to hear if there's a better way to tell, when using setup.py as a configuration file for:
- configuring extension modules
- defining additional metadata for
get_requires_for_build_*
which PEP 517 hook is currently running.
My understanding is that currently this means checking sys.argv. If it contains "egg_info" then the PEP 517 hook for get_requires_for_build_* is running, but if it contains "build" or "build_py" or "build_ext" then one of those 3 setuptools.setup(cmdclass={...} are running (possibly overridden but in this case we don't override them).
When a pure build is requested, no compiled extensions are produced. The setuptools_rust dependency ends up imported-but-not-used. Teach setuptools to avoid build-requiring it in this case.
Closes: #1405