(It's like buses. You wait for ages and then two come along at once.)

😄

It requires the Visual Studio 2019 image (also works for 3.6)

Hmm... The idea for using VS2017 was to test the build script against multiple versions of VS.
Maybe wait a bit longer to see if they are planning to add it to the other images appveyor/ci#3541 (comment)?

I currently only have VS2017 installed on my system and it is what I use to compile Pillow, but that doesn't give immediate test results when updating one of the dependencies (to see if the patches need to be updated), especially since I don't always rebuild dependencies when changing branches.

Sure, let's wait, we're in no rush to update this, we already have GHA testing 3.9.

If AppVeyor aren't going to put 3.9 on VS2017, maybe 3.9/VS2019 and 3.6/VS2017 is possible?

If AppVeyor aren't going to put 3.9 on VS2017, maybe 3.9/VS2019 and 3.6/VS2017 is possible?

Looks like it is not too difficult: https://www.appveyor.com/docs/build-environment/#using-multiple-images-for-the-same-build

Updated!

And it works!

Python 3.6 x64 on VS2017: https://ci.appveyor.com/project/Python-pillow/pillow/builds/35991212/job/nvmoe990w4voffvq?fullLog=true#L129
Python 3.9 32-bit on VS2019: https://ci.appveyor.com/project/Python-pillow/pillow/builds/35991212/job/oeslqec5uu3ekov7?fullLog=true#L129

(11 hours later and Travis CI still hasn't finished...)