Mitigate a regression in the external context

[ilevkivskyi]

Mitigates #5738 by reverting heuristics for type variable return vs instance type outer context changed in #5699. Both versions are kind of unprincipled, but the old one seems to work better in real codebases.

This doesn't touch the core fixes in #5699

cc @euresti could you please double check this also fixes your attr.Factory use cases?

[ilevkivskyi]

The AppVeyor failure is a flake mypy.ipc.IPCException: The NamedPipe at \\.\pipe\dmypy-test-ipc.sock-b'7Avf//Ea'.pipe was not found, cc @ethanhs

Also this passes cleanly on our codebases.

[ethanhs]

@ilevkivskyi Ah, I think that is likely related to whatever failures already observed in #5983. Sorry!

[JukkaL]

This looks like a reasonable thing to do. The previous behavior was arguably more ad hoc than this one.

[ilevkivskyi]

@JukkaL Probably it makes sense to cherry-pick this one.

[gvanrossum]

Not sure we should cp this—we won’t have time to move our internal pins and test it properly.

On Wed, Dec 5, 2018 at 7:20 AM Ivan Levkivskyi ***@***.***> wrote: @JukkaL <https://github.com/JukkaL> Probably it makes sense to cherry-pick this one. — You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub <#6006 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/ACwrMg2_oQ-l-egNegpN9HoNUY4-B_t0ks5u1-Q5gaJpZM4ZBPbV> .

-- --Guido (mobile)

[JukkaL]

This is a fundamental enough change that we should test this internally before a release.

[gvanrossum]

Then let's leave it for the 0.660 release. The previous pin move took me all afternoon.