importing torch in setup.py will cause arcane exceptions when xformers is added without versions

[doctorpangloss]

https://github.com/facebookresearch/xformers/blame/0ec6aa244f3fbf1a077782bbf3ac8e6f2e4d1d16/setup.py#L23C5-L23C5

setup logs:

INFO: pip is looking at multiple versions of xformers to determine which version is compatible with other requirements. This could take a while.
Collecting xformers (from sd-scripts@ file://C:/Users/bberman/Documents/sd-scripts->artworkspace==0.1)
  Downloading xformers-0.0.22.post4-cp311-cp311-win_amd64.whl (97.9 MB)
     ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 97.9/97.9 MB 11.9 MB/s eta 0:00:00
  Using cached xformers-0.0.22-cp311-cp311-win_amd64.whl (97.6 MB)
  Downloading xformers-0.0.21-cp311-cp311-win_amd64.whl (97.5 MB)
     ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 97.5/97.5 MB 18.7 MB/s eta 0:00:00
  Using cached xformers-0.0.20-cp311-cp311-win_amd64.whl (97.6 MB)
Collecting pyre-extensions==0.0.29 (from xformers->sd-scripts@ file://C:/Users/bberman/Documents/sd-scripts->artworkspace==0.1)
  Using cached pyre_extensions-0.0.29-py3-none-any.whl (12 kB)
Collecting xformers (from sd-scripts@ file://C:/Users/bberman/Documents/sd-scripts->artworkspace==0.1)
  Downloading xformers-0.0.16.tar.gz (7.3 MB)
     ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 7.3/7.3 MB 17.2 MB/s eta 0:00:00
  Installing build dependencies ... done
  Getting requirements to build wheel ... error
  error: subprocess-exited-with-error

  × Getting requirements to build wheel did not run successfully.
  │ exit code: 1
  ╰─> [20 lines of output]
      Traceback (most recent call last):
        File "C:\Users\bberman\Documents\Art-Workspace\venv\Lib\site-packages\pip\_vendor\pyproject_hooks\_in_process\_in_process.py", line 353, in <module>
          main()
        File "C:\Users\bberman\Documents\Art-Workspace\venv\Lib\site-packages\pip\_vendor\pyproject_hooks\_in_process\_in_process.py", line 335, in main
          json_out['return_val'] = hook(**hook_input['kwargs'])
                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
        File "C:\Users\bberman\Documents\Art-Workspace\venv\Lib\site-packages\pip\_vendor\pyproject_hooks\_in_process\_in_process.py", line 118, in get_requires_for_build_wheel
          return hook(config_settings)
                 ^^^^^^^^^^^^^^^^^^^^^
        File "C:\Users\bberman\AppData\Local\Temp\1\pip-build-env-b9gnoz9z\overlay\Lib\site-packages\setuptools\build_meta.py", line 325, in get_requires_for_build_wheel
          return self._get_build_requires(config_settings, requirements=['wheel'])
                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
        File "C:\Users\bberman\AppData\Local\Temp\1\pip-build-env-b9gnoz9z\overlay\Lib\site-packages\setuptools\build_meta.py", line 295, in _get_build_requires
          self.run_setup()
        File "C:\Users\bberman\AppData\Local\Temp\1\pip-build-env-b9gnoz9z\overlay\Lib\site-packages\setuptools\build_meta.py", line 480, in run_setup
          super(_BuildMetaLegacyBackend, self).run_setup(setup_script=setup_script)
        File "C:\Users\bberman\AppData\Local\Temp\1\pip-build-env-b9gnoz9z\overlay\Lib\site-packages\setuptools\build_meta.py", line 311, in run_setup
          exec(code, locals())
        File "<string>", line 23, in <module>
      ModuleNotFoundError: No module named 'torch'
      [end of output]

Observe setup.py imports torch, but my pyproject.toml has:

[build-system]
requires = ["setuptools", "wheel", "pip"]
build-backend = "setuptools.build_meta"

aka requires does not contain torch, so your setup.py cannot import it. You will have to do something else. I understand the import torch line has been around since this package was authored, but it looks like pip has changed in the meantime to start this isolation process. There will be a lot of inertia on your team around this code. Nonetheless, fixing it will probably resolve a lot of issues people are reporting.