[BUG] Running with --prefix leads to expected str, bytes or os.PathLike object, not NoneType

[gshtras]

setuptools version

80.0.0

Python version

3.12

OS

Ubuntu 22.04

Additional environment information

No response

Description

Using python setup.py develop with --prefix results in an error:
TypeError: expected str, bytes or os.PathLike object, not NoneType
Due to https://github.com/pypa/setuptools/blob/main/setuptools/command/develop.py#L37
+ ['--index-url', self.index_url] * bool(self.prefix) resolves to ['--index-url', None]

Expected behavior

python setup.py develop --prefix ~/.local should not crash

How to Reproduce

Run python setup.py develop --prefix ~/.local with setuptools==80 on a repo that is using setuptools, such as https://github.com/ROCm/vllm

Output

Traceback (most recent call last):
  File "/root/vllm/setup.py", line 678, in <module>
    setup(
  File "/usr/local/lib/python3.12/dist-packages/setuptools/__init__.py", line 117, in setup
    return distutils.core.setup(**attrs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/dist-packages/setuptools/_distutils/core.py", line 186, in setup
    return run_commands(dist)
           ^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/dist-packages/setuptools/_distutils/core.py", line 202, in run_commands
    dist.run_commands()
  File "/usr/local/lib/python3.12/dist-packages/setuptools/_distutils/dist.py", line 1002, in run_commands
    self.run_command(cmd)
  File "/usr/local/lib/python3.12/dist-packages/setuptools/dist.py", line 1104, in run_command
    super().run_command(command)
  File "/usr/local/lib/python3.12/dist-packages/setuptools/_distutils/dist.py", line 1021, in run_command
    cmd_obj.run()
  File "/usr/local/lib/python3.12/dist-packages/setuptools/command/develop.py", line 39, in run
    subprocess.check_call(cmd)
  File "/usr/lib/python3.12/subprocess.py", line 408, in check_call
    retcode = call(*popenargs, **kwargs)
              ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.12/subprocess.py", line 389, in call
    with Popen(*popenargs, **kwargs) as p:
         ^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.12/subprocess.py", line 1026, in __init__
    self._execute_child(args, executable, preexec_fn, close_fds,
  File "/usr/lib/python3.12/subprocess.py", line 1885, in _execute_child
    self.pid = _fork_exec(
               ^^^^^^^^^^^
TypeError: expected str, bytes or os.PathLike object, not NoneType

[jaraco]

Oops. Yeah, I see the error. The logic there should be to use self.index_url in both parts of the computation.

[jaraco]

Thanks for the report. Fix going out as v80.0.1.