Invalid version found by pip for flit install -s packages

[ivirshup]

flit symlinked installed packages with build numbers are being overwritten with versions from pypi if any package that depends on it are installed. Here's an example:

conda create -yn flit-deps python=3.8 flit
conda activate flit-deps
gh repo clone theislab/scanpy
cd scanpy
gh pr checkout 1527  # The PR that uses flit
flit install -s --deps=develop

cd ~  # Move out of the directory

python -c "import scanpy; print(scanpy.__version__)"
# 1.8.0.dev50+g8e703b89.d20210301 

pip install scvelo  # Package that depends on scanpy. Truncated output:
# ...
# Collecting scanpy>=1.5
#  Using cached scanpy-1.7.1-py3-none-any.whl (10.3 MB)
# ...
#  Attempting uninstall: scanpy
#    Found existing installation: scanpy 1.8.0.dev50-g8e703b89.d20210301
#    Uninstalling scanpy-1.8.0.dev50-g8e703b89.d20210301:
#      Successfully uninstalled scanpy-1.8.0.dev50-g8e703b89.d20210301

python3 -c "import scanpy; print(scanpy.__version__)"
# 1.7.1

It looks to me like pip is getting incorrect version information about the package, similar to the problem raised in #383 and addressed in #388. However, in this case the package is not a wheel.

[flying-sheep]

Might also be a pip problem: pypa/pip#9670

[flying-sheep]

Fixed! See the check here: scverse/scanpy#1702 (comment)