The newest setuptools v49.2.0 warns:

/home/travis/virtualenv/python3.9-dev/lib/python3.9/site-packages/setuptools/distutils_patch.py:25: UserWarning: Distutils was imported before Setuptools. This usage is discouraged and may exhibit undesirable behaviors or errors. Please use Setuptools' objects directly or at least import Setuptools first.

(From pypa/setuptools#2256 / pypa/setuptools#2230)

And results in a build error:

/home/travis/virtualenv/python3.9-dev/lib/python3.9/site-packages/Pillow-7.3.0.dev0-py3.9-linux-x86_64.egg/PIL/Image.py:115: RuntimeWarning: The _imaging extension was built for another version of Pillow or PIL:
Core version: None
Pillow version: 7.3.0.dev0

https://travis-ci.org/github/hugovk/Pillow/jobs/707725016

Importing setuptools before distuils in setup.py gets rid of the warning but not the build error:

master...hugovk:3.9-upgrade-setuptools2

https://travis-ci.org/github/hugovk/Pillow/builds/707729489

And upgrading setuptools for all Python versions on Travis also has the same build error (not tested on Mac/Windows/other CIs):

master...hugovk:3.9-upgrade-setuptools3

https://travis-ci.org/github/hugovk/Pillow/builds/707730154

Will report to setuptools, and they're already reconsidering the strategy: pypa/setuptools#2259.

Reported: pypa/setuptools#2261.

Also macOS (and Linux) on GHA:

• https://github.com/hugovk/Pillow/actions/runs/167763122
• master...hugovk:3.9-upgrade-setuptools4

(Not Windows, but I've not checked it actually upgraded.)

(Not Windows, but I've not checked it actually upgraded.)

You only updated the MSYS script, and that build (surprisingly) passes with 49.1.3.

I added the upgrade to the main Windows build and it also fails:

• https://github.com/nulano/Pillow/runs/866809418?check_suite_focus=true#step:21:803
• master...nulano:upgrade-setuptools

I've concluded that this error was also introduced in setuptools 47.3.2. I've created pypa/setuptools#2297 to resolve.

Hopefully this will pass now pypa/setuptools#2297 is merged and setuptools 49.3.2 is released 🤞

Just copying my comment from #4858: GHA 3.9-dev has been updated and now also has a broken setuptools version.

Thanks, updated to upgrade on GHA for 3.9-dev as well.