Query the list of packages in a not-yet-installed source tree

[zackw]

Given a source tree (probably, but not necessarily, a VCS checkout), that uses setuptools as its build backend, with all relevant configuration in pyproject.toml, is there an officially supported way to ask setuptools to run package discovery (if necessary), but not actually build anything, and then tell me the values it has determined for the packages and py_modules lists?

I can get what I want from distutils.core.run_setup("setup.py", stop_after="config") but that smells like a legacy API that might not be sticking around.

[webknjaz]

That's not exactly covered by PEP 517. There's some info you might be able to retrieve via https://build.pypa.io/en/stable/api.html#build.util.project_wheel_metadata. But in general, most tooling interfaces on the level of the core packaging metadata. And backend internals aren't exposed in such a setup. Though, maybe the produced metadata's file list would be what you're looking for. Try poking around PEP 517 and see.

[webknjaz]

Maybe inspecting the PEP 660's “fake wheels” would be better for you, though. And this wouldn't be really scoped to setuptools and work with any backend.