pip: pip install -U breaks dependencies

Environment

• pip version: 20.0.2
• Python version: 3.8.2
• OS: MacOS
• python installed by brew to avoid conflict with OS’s python.

$ uname -a

Darwin illbebachs-iMac 19.4.0 Darwin Kernel Version 19.4.0: Wed Mar  4 22:28:40 PST 2020; root:xnu-6153.101.6~15/RELEASE_X86_64 x86_64

Related Issue

#7744 Handle conflicts from installed packages when updating other packages

Description

pip install -U breaks dependencies on installed packages, even when --upgrade-strategy=only-if-needed is specified on the command line. In the script below, I create a clean environment using venv and install pylint. pip install -U breaks dependencies of installed packages.

pip recognizes and reports the error regarding the dependency, but performs the upgrade anyway.

Expected behavior

pip should report the error and not perform the upgrade.

How to Reproduce

I ran the following script to demonstrate the error

#!/bin/bash

which python3.8
python3.8 --version

# setup a clean environment for testing
rm -rf clean_slate
python3.8 -m venv clean_slate
. clean_slate/bin/activate
which pip
which python

# upgrade basic packages to latest version
pip install --upgrade pip setuptools
pip --version
pip list

pip install pylint

pip list
pip check
pip list --outdated

# now perform the upgrade, where pip should fail
pip install --upgrade --upgrade-strategy=only-if-needed wrapt
pip check

Output

$ which python3.8
/usr/local/bin/python3.8

$ python3.8 --version
Python 3.8.2

$ rm -rf clean_slate

$ python3.8 -m venv clean_slate

$ . clean_slate/bin/activate

$ which pip
/Users/illbebach/clean_slate/bin/pip

$ which python
/Users/illbebach/clean_slate/bin/python

$ pip install --upgrade pip setuptools
... verbose output omitted ...
Successfully installed pip-20.0.2 setuptools-46.1.3

$ pip --version
pip 20.0.2 from /Users/illbebach/clean_slate/lib/python3.8/site-packages/pip (python 3.8)

$ pip list
Package    Version
---------- -------
pip        20.0.2 
setuptools 46.1.3 

$ pip install pylint
... verbose output omitted ...
Successfully installed astroid-2.3.3 isort-4.3.21 lazy-object-proxy-1.4.3 mccabe-0.6.1 pylint-2.4.4 six-1.14.0 wrapt-1.11.2

$ pip list
Package           Version
----------------- -------
astroid           2.3.3  
isort             4.3.21 
lazy-object-proxy 1.4.3  
mccabe            0.6.1  
pip               20.0.2 
pylint            2.4.4  
setuptools        46.1.3 
six               1.14.0 
wrapt             1.11.2 

$ pip check
No broken requirements found.

$ pip list --outdated
Package Version Latest Type 
------- ------- ------ -----
wrapt   1.11.2  1.12.1 sdist

$ pip install --upgrade --upgrade-strategy=only-if-needed wrapt
Collecting wrapt
  Using cached wrapt-1.12.1.tar.gz (27 kB)
ERROR: astroid 2.3.3 has requirement wrapt==1.11.*, but you'll have wrapt 1.12.1 which is incompatible.
Installing collected packages: wrapt
  Attempting uninstall: wrapt
    Found existing installation: wrapt 1.11.2
    Uninstalling wrapt-1.11.2:
      Successfully uninstalled wrapt-1.11.2
    Running setup.py install for wrapt: started
    Running setup.py install for wrapt: finished with status 'done'
Successfully installed wrapt-1.12.1

$ pip check
astroid 2.3.3 has requirement wrapt==1.11.*, but you have wrapt 1.12.1.