abi3-py36 now passes tests

[kngwyu]

Now cargo test --features=abi3-py36 fails since ffi::PyEval_InitThreads() is called after Py_InitializeEx.
So now py36 build is not actually forward-compatible.
We have a small fix for this problem (this PR), but this also suggests that py3* build can be broken in the future version.
Though I'm not sure the breakage is likely to happen in the user code, maybe we want to add a note about it.

[kngwyu]

Oops, it looks like that datetime is not declared with Py_LIMITED_API....
I'm glad to find this major bug before releasing 0.13!

[davidhewitt]

👍 thanks, that's a nice catch!

I think a couple of these changes are done with the goal of minimising LOC & optimizations, but I don't agree with them. I'd prefer we kept what we had before for those cases. See my other comments.

[davidhewitt]

I merged #1329 which should fix the pypy issues - if you rebase on master CI should hopefully be green 🤞

[davidhewitt]

Ok I merged #1331 and now hopefully this will work. I'm going to rebase this on master and then merge if it's ok.

[davidhewitt]

Ugh, still failing pypy tests!

I think the issue is that on pypy we can build the tests, but can't ever run them.

I'm going to work on yet another PR to improve the pypy CI...

[kngwyu]

Thanks.
Could I help to debug?
What is the precise commit where this starts failing?
#1325?

[davidhewitt]

Ah, yes, that's it - for now I have disabled the pypy abi3-py36 tests being built; that should fix this PR and then I'll open a new PR later which re-enables building the tests.

[davidhewitt]

🎉