check usage f urllib3

[memsharded]

Changelog: Bugfix: Recent liburl3 1.26 library updates is breaking the constraints in Conan requirements.txt as requests 2.24 has a limitation for liburl3. This PR constrains liburl3 version to be less than 1.26, so it does not break with requests 2.24.
Docs: Omit

Close #8041

Note: we might need to backport this to older Conan releases that might also break in prod.

#tags: slow, svn
#revisions: 1

[jgsogo]

1.25.4 and 1.25.5 contained a bug that was affecting us. New requests 2.25.0 (to be released today) will be compatible with new urllib3 1.26.

OTH, the new pip resolution algorithm 2020-resolver (should be the default very soon, it says October 2020) won't resolve to the conflicting dependencies, it looks like there is some metadata in the packages. This works for me:

pip install --use-feature=2020-resolver -U -r conans/requirements.txt

[lasote]

It is a bit weird because it should be able to resolve the conflict. The restriction we provide block only two versions (buggy versions).
Actually using the new pip resolver works.

• If I don't use the new resolver:

ERROR: After October 2020 you may experience errors when installing or updating packages. This is because pip will change the way that it resolves dependency conflicts.
We recommend you use --use-feature=2020-resolver to test your packages with the new resolver before it becomes the default.                                                                                                                                                    
requests 2.24.0 requires urllib3!=1.25.0,!=1.25.1,<1.26,>=1.21.1, but you'll have urllib3 1.26.0 which is incompatible.                                                     

• Using the new resolver (pip install conan --upgrade --use-feature=2020-resolver)

Collecting urllib3!=1.25.4,!=1.25.5
  Using cached urllib3-1.25.11-py2.py3-none-any.whl (127 kB)
Requirement already satisfied: pyparsing>=2.0.2 in /home/luism/.virtualenvs/kk/lib/python3.7/site-packages (from packaging->deprecation<2.1,>=2.0->conan) (2.4.7)
Requirement already satisfied: six<=1.15.0,>=1.10.0 in /home/luism/.virtualenvs/kk/lib/python3.7/site-packages (from conan) (1.15.0)
Installing collected packages: urllib3
  Attempting uninstall: urllib3
    Found existing installation: urllib3 1.26.0
    Uninstalling urllib3-1.26.0:
      Successfully uninstalled urllib3-1.26.0
Successfully installed urllib3-1.25.11

[jgsogo]

It is the new algorithm, no metadata, requests already says urllib3<1.26:

https://github.com/psf/requests/blob/0797c61fd541f92f66e409dbf9515ca287af28d2/setup.py#L47

[jgsogo]

pip changelog says new algorithm will be the default in version 20.3 (expected)

https://pip.pypa.io/en/stable/news/

[lasote]

So, @jgsogo do we agree we shouldn't remove these constraints but introduce <1.26?

[charliekang]

pip added --use-feature=2020-resolver which worked