20.2.1 Regression - Pip fails installing depdencies from site-packages in virtualenv. Install fails completely with no repo

[dfresh613]

Hi, I think this has been discussed in a few other issues, and the #8702 seems to fix it for us. But I wanted to provide this example which illustrates how impactful this bug actually is, and perhaps request you to yank the 20.2.1 version from the pypi repo.

Environment

• pip version: 20.2.1
• Python version:3.7
• OS: any

Dockerfile that illustrates this issue:

FROM python:3.7
RUN pip install virtualenv requests
RUN /usr/local/bin/virtualenv --system-site-packages tst
RUN /tst/bin/pip3.7 install --upgrade pip==20.2.1 && /tst/bin/pip3.7 install --proxy 127.0.0.1 --retries 0 --timeout 1 requests

Description
In the above example, the requests library is installed, and made available system site wide. A virtualenv is then created (including system site packages).

When we attempt to install requests (or any package that requires requests) the install will always fail if there is no connection to a remote repo that contains that package. (I add a fake proxy --proxy127.0.0.1 to simulate no access to repo)

Expected behavior
Pip installs requests correctly in the virtualenv above example. You'll find that if you change the pip version any version <20.2.1, it succeeds.

Only this version 20.2.1 released 3 days ago began to cause problems.

Output

ERROR: Could not find a version that satisfies the requirement requests (from versions: none)
ERROR: No matching distribution found for requests

Any thoughts on when you will merge #8702 and potentially release a 20.2.2? Or perhaps yank the current 20.2.1 version?

[uranusjr]

Yanking is likely not a good idea since that would make people needing the fixes it includes very unhappy. A bugfix release will be made as soon as possible to include the aforementioned PR.