pip download fails due to missing version in metadata

[staer]

Using pip (v21.3.1) and setuptools (v59.5.0) the following command to download pytest fails:

pip download --no-build-isolation --no-binary :all: pytest==6.2.5

Collecting pytest==6.2.5
  Downloading pytest-6.2.5.tar.gz (1.1 MB)
     |████████████████████████████████| 1.1 MB 1.9 MB/s            
  Preparing metadata (pyproject.toml) ... done
  WARNING: Requested pytest==6.2.5 from https://files.pythonhosted.org/packages/4b/24/7d1f2d2537de114bdf1e6875115113ca80091520948d370c964b88070af2/pytest-6.2.5.tar.gz#sha256=131b36680866a76e6781d13f101efb86cf674ebb9762eb70d3082b6f29889e89, but installing version 0.0.0
WARNING: Discarding https://files.pythonhosted.org/packages/4b/24/7d1f2d2537de114bdf1e6875115113ca80091520948d370c964b88070af2/pytest-6.2.5.tar.gz#sha256=131b36680866a76e6781d13f101efb86cf674ebb9762eb70d3082b6f29889e89 (from https://pypi.org/simple/pytest/) (requires-python:>=3.6). Requested pytest==6.2.5 from https://files.pythonhosted.org/packages/4b/24/7d1f2d2537de114bdf1e6875115113ca80091520948d370c964b88070af2/pytest-6.2.5.tar.gz#sha256=131b36680866a76e6781d13f101efb86cf674ebb9762eb70d3082b6f29889e89 has inconsistent version: filename has '6.2.5', but metadata has '0.0.0'
ERROR: Could not find a version that satisfies the requirement pytest==6.2.5 (from versions: 2.0.0, <SNIP ALL VERSIONS>, 6.2.5)
ERROR: No matching distribution found for pytest==6.2.5

I believe this is due to setup.cfg having no version specified in the [metadata] section. I believe something along the lines of:

version = attr: pytest.__version__

might get it working.

[nicoddemus]

I'm just guessing here, but perhaps --no-build-isolation bypasses setuptools-scm?

cc @RonnyPfannschmidt

[RonnyPfannschmidt]

@nicoddemus yes, we should probably ensure setup.py fails harshly if the required versions are missing

im also confused as to why pip skips build requires

[staer]

Some additional datapoints:

Using the legacy-resolver works fine:

pip download --no-binary :all: --use-deprecated=legacy-resolver --no-build-isolation pytest==6.2.5

And not using no-build-isolation also works fine:

pip download --no-binary :all: pytest==6.2.5

[RonnyPfannschmidt]

@staer i beleive that part is a pip bug, - pytest can add a error to make it more visible