Pip does not detect library name clashes

[solney-syn]

Description

It's possible to install two packages that both install to the same location, e.g both semver and node-semver install to semver (noted here)
Although pip cannot prevent this it would be helpful if could alert the user.

This would be beneficial as otherwise the problem can lurk undetected for some time and be more difficult to fix later, especially if clash is caused by transitive dependencies.

Expected behavior

If this occurs then pip should fail, informing the user of possible approaches to fix the problem e.g using separate venvs.

$ pip install semver node-semver
Error: Namespace clash. Both packages use the `semver` namespace

pip version

22.1.2

Python version

3.8.10

OS

Linux

How to Reproduce

1. Create venv python3 -m venv env
2. Get latest pip env/bin/pip install -U pip
3. Install the two packages env/bin/pip install semver node-semver
4. Try to import from semver env/bin/python -c 'from semver import VersionInfo'

Output

+ python3 -m venv env
+ env/bin/pip install -U pip
Collecting pip
  Using cached pip-22.1.2-py3-none-any.whl (2.1 MB)
Installing collected packages: pip
  Attempting uninstall: pip
    Found existing installation: pip 20.0.2
    Uninstalling pip-20.0.2:
      Successfully uninstalled pip-20.0.2
Successfully installed pip-22.1.2
+ env/bin/pip install semver node-semver
Collecting semver
  Using cached semver-2.13.0-py2.py3-none-any.whl (12 kB)
Collecting node-semver
  Using cached node_semver-0.8.1-py3-none-any.whl (24 kB)
Installing collected packages: node-semver, semver
Successfully installed node-semver-0.8.1 semver-2.13.0
+ env/bin/python -c 'from semver import VersionInfo'
Traceback (most recent call last):
  File "<string>", line 1, in <module>
ImportError: cannot import name 'VersionInfo' from 'semver' (/home/solney/tmp/env/lib/python3.8/site-packages/semver/__init__.py)

Code of Conduct

• I agree to follow the PSF Code of Conduct.

[pradyunsg]

Duplicate of #4625