`ensurepip` fails with `importlib.metadata` backend

Description

In Debian, we use the pip from our pip package with ensurepip. We’ve noticed with 3.11, and pip 22.1.1, ensurepip isn’t doing anything any more.

The relevant change is that the importlib.metadata is the default backend with Python 3.11. If we force it back to the pkg_resources backend, it works.

Expected behavior

ensurepip is expected to install pip. It doesn’t do anything, any more.

pip version

22.1.2+ dc7abcada7e263e80af6c8d4ea2147c067c78d01

Python version

3.11+ f9d0240db809fbb4443dc8f96a18e4c49af3fb7f

OS

Linux

How to Reproduce

1. Install Python 3.11.
2. Build / download a current (>= 22.1) pip wheel. Install it into ensurepip/_bundled/ in your Python installation.
3. Update _PIP_VERSION in ensurepip/__init__.py to refer to the new version.
4. python3.11 -m venv testve
5. ls testve/lib/python3.11/site-packages/

This should not be empty, but will be.

For extra debugging:

1. testve/bin/python -Im ensurepip --upgrade --default-pip -v

Output

Using pip 22.2.dev0 from /tmp/tmp3dhtsvpz/pip-22.2.dev0-py3-none-any.whl/pip (python 3.11)
Looking in links: /tmp/tmp3dhtsvpz
Requirement already satisfied: setuptools in ./tmp3dhtsvpz/setuptools-58.1.0-py3-none-any.whl (58.1.0)
Requirement already satisfied: pip in ./tmp3dhtsvpz/pip-22.2.dev0-py3-none-any.whl (22.2.dev0)

Code of Conduct

• I agree to follow the PSF Code of Conduct.

[pradyunsg]

Indeed, let’s do both then. 😃

[uranusjr]

Huh, pkg_resources explicitly ignores .dist-info in a wheel, but importlib.metadata does not:

https://github.com/pypa/pip/blob/dc7abcada7e263e80af6c8d4ea2147c067c78d01/src/pip/_vendor/pkg_resources/__init__.py#L1978-L1981

As you can tell from comment, the logic is pretty outdated and is arguably a bug, but this is relied by pip and “works”. I’ll work on a fix to do this properly.