pip 21.3+ in-tree builds with setuptools, do not clean local build directories

Description

Given a requirements.txt including a local package path, installing them will litter the local path with in-tree build folders.

This is slightly bloating docker builds and causing some issues due to build artifacts permissions that force us to clean every local build folder with

WORKDIR /path/to/package-1
RUN python setup.py clean --all
WORKDIR /path/to/package-2
RUN python setup.py clean --all
# etc

but note this won't slim image sizes either.

Expected behavior

Previous pip versions built local packages in folders like /tmp/pip-req-build-XXXXXXX/ . Regardless of being in-tree or out-of-tree, the point is those folders vanished at the end of a pip install instruction unless the --no-clean flag was used.

pip version

21.3

Python version

3.9.7

OS

GNU/Linux + Docker 20.10.8

How to Reproduce

1. git clone https://github.com/pypa/sampleproject.git /tmp/sampleproject
2. pip install --use-feature=in-tree-build /tmp/sampleproject
3. find /tmp/sampleproject/build

Output

/tmp/sampleproject/build
/tmp/sampleproject/build/bdist.linux-x86_64
/tmp/sampleproject/build/lib
/tmp/sampleproject/build/lib/sample
/tmp/sampleproject/build/lib/sample/__init__.py
/tmp/sampleproject/build/lib/sample/simple.py
/tmp/sampleproject/build/lib/sample/package_data.dat

Code of Conduct

• I agree to follow the PSF Code of Conduct.

Reproduce the behavior with sampleproject using pip install --use-feature=in-tree-build /tmp/sampleproject, then inspect the build cleanup path involved in the setuptools invocation. Compare the generated build directory with the expected temporary-build behavior and verify that a completed install does not leave local build artifacts behind.