#637 failed for PyPy on Ubuntu and macOS (but not Windows):

          self.link(
        File "/tmp/pip-build-env-0i2_clgx/overlay/lib/pypy3.10/site-packages/setuptools/_distutils/unixccompiler.py", line 268, in link
          linker = (
      TypeError: 'NoneType' object is not subscriptable (key slice(None, None, None))

https://github.com/ultrajson/ultrajson/actions/runs/10650149917/job/29521178562?pr=637

Our last passing build was on 1st August: #636 (these regular dependabot PRs are useful after all!)

It looks like a setuptools thing. I tried setuptools 72.1, the current on 1st August, which worked, and found the first failure happened with 72.2, released on 2nd August.

https://setuptools.pypa.io/en/stable/history.html#v72-2-0

setuptools 72.2 had changes related to distutils and compilers, which tracks with the traceback above:

Merged with pypa/distutils@b7ee725f3 including: Support for Pathlike objects in data files and extensions (pypa/distutils#272, pypa/distutils#237), native support for C++ compilers (pypa/distuils#228) and removed unused get_msvcr() (pypa/distutils#274). (#4538)

I'll report this to setuptools.

And let's pin an upper setuptools version for the build backend for now.