stdlib/2/builtins.pyi is also a symlink; does that not cause problems? I don't have Windows available to test.

That mystified me too, but apparently mypy carefully never follows the symlink -- it always loads __builtins__.pyi. There are also a few other symlinks -- I am guessing those don't get tested at all.

Unless I totally misunderstood the error from AppVeyor:

typeshed\stdlib\3\ntpath.pyi:1: error: Name 'posixpath' is not defined
typeshed\stdlib\3\macpath.pyi:1: error: Name 'posixpath' is not defined

FWIW I stack-overflowed this and the situation is dear: http://stackoverflow.com/questions/5917249/git-symlinks-in-windows

I don't really want to write a post-checkout script so I guess we should get rid of the symlinks.

That's unfortunate, I'm worried that we'll end up with changes being applied to only one of the files. Maybe we can add a test that ensures that the contents of __builtin__.pyi and builtins.pyi (and the other groups of symlinked files) are exactly the same.

You're also welcome to write that post-checkout script. :-)

FWIW we also have this problem in our Windows wheels -- I just checked out https://pypi.python.org/pypi/mypy/0.501 and sadly it looks like the file .../stdlib/2/builtins.pyi there is a plain text file containing the text __builtin__.pyi (i.e. the text contents of the symlink). I guess we're lucky it hasn't bitten anyone yet so far.