[FR] Allow bootstraping setuptools by running dependencies from source

[FFY00]

What's the problem this feature will solve?

setuptools requires wheel to be installed to bootstrap itself, but wheel requires setuptools to build, preventing bootstrapping.

Even though setuptools now bootstraps itself via a PEP 517 builder, not everyone is able to do the same. Linux distributions, for example, need to bootstrap it from scratch.

Describe the solution you'd like

I would like an option, perhaps an environment variable, to skip the dependency checks, and to make the bdist_wheel command always available.
The easiest way to do this bootstrapping is to run everything from source, which trips up setuptools' dependency checks, and also as a consequence makes the bdist_wheel command unavailable.

Alternative Solutions

I have written https://github.com/FFY00/python-bootstrap to help with this task, but currently, I need to run setup.py egg_info on setuptools, copy that to the package directory, in order to trick setuptools to think it is installed, and then do the same for wheel, only after that I can actually build wheels for setuptools and wheel.
https://github.com/FFY00/python-bootstrap/blob/4004fda86bc82470b0ee1b564764f8ba9960b493/bootstrap/build.py#L43
https://github.com/FFY00/python-bootstrap/blob/bf68a5ff74706e348de1f3dddeaf51bc5f37a449/bootstrap/__init__.py#L109
See #2088 (comment) for more details.

Ideally, setuptools would actually be able to bootstrap itself without any dependencies.
See https://github.com/takluyver/flit/tree/master/flit_core for example.

Additional context

No response

Code of Conduct

• I agree to follow the PSF Code of Conduct

[layday]

Short of merging wheel into setuptools or building a setuptools wheel without the aid of the wheel package, what would be a solution to this issue?

[layday]

Can we duplicate all of the necessary entry points in https://github.com/pypa/setuptools/blob/main/bootstrap.egg-info/entry_points.txt, would that work to avoid this little dance?

[nanonyme]

Perhaps indeed wheel could be vendored through git submodules and then added to sdist but not installed or added to final wheel package. backend-path might allow setuptools to consume it while it is creating wheel of itself.

[nanonyme]

This is btw a huge problem until solved. It means setup.py install must be kept indefinitely for bootstrapping setuptools unless I'm missing something. The non-legacy build chain is.

1. flit_core
2. pypa-install
3. pyproject-hooks
4. packaging
5. pypa-build

and then you need hit a dependency cycle where setuptools needs wheel and wheel needs setuptools. You need to resolve that before building pip. Maybe this should be re-classified as a bug rather than enhancement?

[astrojuanlu]

@nanonyme see pypa/wheel#501

[nanonyme]

Fair, if it will get done that way.

[SpecLad]

FWIW, it is possible to bootstrap setuptools and wheel without using setup.py install, although it is a bit hacky:

1. Unpack the setuptools and wheel sdists.
2. In the setuptools source directory, run PYTHONPATH=../wheel-x.y.z/src python setup.py bdist_wheel. Install the resulting wheel.
3. In the wheel source directory, run PYTHONPATH=src python setup.py bdist_wheel. Install the resulting wheel.