Older pip being used for sdist crawl?

[JustinTArthur]

I notice a lot of missing setup.py errors from the sdist crawl and I'm wondering if maybe an older version of pip is being used? pip 19.3.1 and greater should be able to construct wheels without setup.py if there's a pyproject.toml in the sdist with build instructions.

[DavHau]

Currently setuptools is used directly and that obviously reduces support to packages being built via setuptools.
I'm not sure how exactly building wheels without setup.py works for most projects.
I know that there are other build backends besides setuptools which can be defined via PEP-518.
What build backend do those projects use if they are not using setuptools? Maybe you could provide an example.

[JustinTArthur]

Most of the ones I sampled are using setuptools, but newer versions of setuptools that use setup.cfg instead of setup.py, often with PEP-518 pyproject.toml included in the sdist with setuptools instructions.