System setuptools leaks into isolated build environment

Description

My project uses a custom in-tree build backend that wraps setuptools.build_meta and its build-system hooks implementation. I’m trying to add support for editable installs. I’m running on a Fedora 36 box, and the system has setuptools 59 installed via the system package manager. Therefore, I request a higher setuptools version in pyproject.toml. Looks like pip actually installs the higher setuptools, but eventually the older one from the system is picked.

Expected behavior

pip should use the requested version of setuptools.

pip version

22.2.2

Python version

3.10

OS

Fedora Linux 36

How to Reproduce

• pyproject.toml

[project]
name = "foo"
version = "0.0.1"

[build-system]
requires = ["setuptools >= 64"]
build-backend = "builder"
backend-path = ["."]

• builder.py

def get_requires_for_build_editable(config_settings=None):
    import setuptools
    assert 0, f"{setuptools.__version__} {setuptools}"
    from setuptools import build_meta as backend
    return backend.get_requires_for_build_editable(
        config_settings,
    )

def prepare_metadata_for_build_editable(
    metadata_directory,
    config_settings=None,
):
    from setuptools import build_meta as backend
    return backend.prepare_metadata_for_build_editable(
        metadata_directory,
        config_settings,
    )

def build_editable(
    wheel_directory,
    config_settings=None,
    metadata_directory=None,
):
    from setuptools import build_meta as backend
    return backend.build_editable(
        wheel_directory,
        config_settings,
        metadata_directory,
    )

Note the line assert 0, f"{setuptools.__version__} {setuptools}" in get_requires_for_build_editable()! I need that line to easily show the root of the issue.

Output

Use `pip` to install in editable mode:


$ pip install -e .
Defaulting to user installation because normal site-packages is not writeable
Obtaining file:///home/dalcinl/tmp/pip-bug
  Installing build dependencies ... done
  Checking if build backend supports build_editable ... done
  Getting requirements to build editable ... error
  error: subprocess-exited-with-error
  
  × Getting requirements to build editable did not run successfully.
  │ exit code: 1
  ╰─> [10 lines of output]
      Traceback (most recent call last):
        File "/home/dalcinl/.local/lib/python3.10/site-packages/pip/_vendor/pep517/in_process/_in_process.py", line 363, in <module>
          main()
        File "/home/dalcinl/.local/lib/python3.10/site-packages/pip/_vendor/pep517/in_process/_in_process.py", line 345, in main
          json_out['return_val'] = hook(**hook_input['kwargs'])
        File "/home/dalcinl/.local/lib/python3.10/site-packages/pip/_vendor/pep517/in_process/_in_process.py", line 144, in get_requires_for_build_editable
          return hook(config_settings)
        File "/home/dalcinl/tmp/pip-bug/builder.py", line 3, in get_requires_for_build_editable
          assert 0, f"{setuptools.__version__} {setuptools}"
      AssertionError: 59.6.0 <module 'setuptools' from '/usr/lib/python3.10/site-packages/setuptools/__init__.py'>
      [end of output]
  
  note: This error originates from a subprocess, and is likely not a problem with pip.
error: subprocess-exited-with-error

× Getting requirements to build editable did not run successfully.
│ exit code: 1
╰─> See above for output.

note: This error originates from a subprocess, and is likely not a problem with pip.

Note the AssertionError line:

AssertionError: 59.6.0 <module 'setuptools' from '/usr/lib/python3.10/site-packages/setuptools/__init__.py'>

I requested "setuptools >= 64" in my requirement, but the older system-wide setuptools is being used.

### Code of Conduct

- [X] I agree to follow the [PSF Code of Conduct](https://www.python.org/psf/conduct/).

[pradyunsg]

I explicitly state that I DO NOT AGREE with being forced to agree with the PSF Code of Conduct to submit this issue. I ticked the box just because I cannot continue otherwise. I hope this requirement for issue submission is an oversight. If not, please close this issue and ignore my report.

It’s not an oversight. Making users explicitly opt in is an intentional choice.

Regardless of what you say, you’re expected to follow the PSF CoC while interacting in this project’s online spaces (and setuptools’). If you violate the CoC in your interactions here at any point, we’ll take action according to the CoC as well. If you have concerns around that, you’re free to not interact with the project. 😃

[pradyunsg]

Consolidating this into https://github.com/pypa/pip/issues/6264.