Ah. Compilation failed on "Windows PR Tests win32" of Azure Pipelines PR:

2019-01-07T15:02:40.9331567Z d:\a\1\s\modules\posixmodule.c(11823): warning C4013: 'GetMaximumProcessorCount' undefined; assuming extern returning int [D:\a\1\s\PCbuild\pythoncore.vcxproj]

... but it pass on "Windows PR Tests win64".

Extract of pythoninfo on "Windows PR Tests win32" from a different PR:

• platform.architecture: 32bit WindowsPE
• platform.platform: Windows-10-10.0.14393-SP0
• sys.version: 3.8.0a0 (remotes/pull/11455/merge:a07376fda, Jan 7 2019, 09:34:24) [MSC v.1915 32 bit (Intel)]

That is a very strange error to get... I can't think of any reason other than a corrupt incremental build, but we don't do incremental builds here.

Perhaps the rebuild when you add a NEWS entry will work?

On IRC, @zware told me:

Looks like you need to set Py_WINVER to 0x0601 in PC/pyconfig.h

It tried to avoid puting this change in this PR to get a PR as small as possible, but it seems like it's not enough.

Note: I already failed to understand such failure in the past: https://bugs.python.org/issue32592#msg318103 Windows is still full of mystery for me :-)

@vstinner Zachary is correct. You'll need to get that first change in before any of the rest will succeed reliably.

I'm okay with reviewing all of the changes together if it's simpler for you to do one PR. But the WINVER update is the critical part.

I don't understand how to remove Vista support. I give up on this PR. If someone else is interested, please go ahead and write a new PR :-)