testing vcs_version target

[AliGouta]

I am new to pants, and this is something we want to adopt within our organization. I was testing different features and was not able to run :
pants export-codegen src/foo:version as mentionned in the doc:

https://www.pantsbuild.org/docs/generating-version-tags

I tried it on a simple project with pants 2.15.0 and also tried to run :

./pants export-codegen src:vcs_version

on this example: https://github.com/benjyw/black/tree/pantsify3

Each time I get the same error. Example of the error :

12:54:43.82 [INFO] Completed: Building setuptools_scm.pex from setuptools-scm_default.lock
12:54:44.21 [INFO] Completed: Run setuptools_scm for helloworld/greet:vcs_version
12:54:44.22 [ERROR] 1 Exception encountered:

Engine traceback:
  in `export-codegen` goal
  in Hydrate the `sources` field - helloworld/greet:vcs_version

ProcessExecutionFailure: Process 'Run setuptools_scm for helloworld/greet:vcs_version' failed with exit code 1.
stdout:

stderr:
Traceback (most recent call last):
  File "/private/var/folders/q8/ww__896s4rqfpt6mhtnblkvh0000gn/T/pants-sandbox-DgFRwT/.cache/pex_root/venvs/cf4a883a550c4c8a817e41f476854a593bfff6da/185060ca67f07b2fc4906338d0f05e510b3e8247/pex", line 243, in <module>
    runpy.run_module(module_name, run_name="__main__", alter_sys=True)
  File "/Users/aligouta/.pyenv/versions/3.8.5/lib/python3.8/runpy.py", line 207, in run_module
    return _run_module_code(code, init_globals, run_name, mod_spec)
  File "/Users/aligouta/.pyenv/versions/3.8.5/lib/python3.8/runpy.py", line 97, in _run_module_code
    _run_code(code, mod_globals, init_globals,
  File "/Users/aligouta/.pyenv/versions/3.8.5/lib/python3.8/runpy.py", line 87, in _run_code
    exec(code, run_globals)
  File "/Users/aligouta/.cache/pants/named_caches/pex_root/venvs/s/7c73d32a/venv/lib/python3.8/site-packages/setuptools_scm/__main__.py", line 83, in <module>
    main()
  File "/Users/aligouta/.cache/pants/named_caches/pex_root/venvs/s/7c73d32a/venv/lib/python3.8/site-packages/setuptools_scm/__main__.py", line 30, in main
    assert version is not None
AssertionError

Use --keep-sandboxes=on_failure to preserve the process chroot for inspection.

The foolowing commande works fine:

/Users/aligouta/.pyenv/versions/3.8.5/bin/python3.8 -m setuptools_scm

Am i missing something ? Thanks !