> Unless your point is that we should _always_ traverse junctions? In 
> which case we have a traverse 'upgrade' scenario (calls to lstat() 
> become calls to stat() when we find out it's a junction).

If we've opened the reparse point to test IO_REPARSE_TAG_SYMLINK, and that's not the case, then we need to reopen with reparsing enabled. This is exactly what Windows API functions do in order to implement particular behavior for just symlinks or just mountpoints. 

For example, if we've opened an HSM reparse point, we must reopen to let the file-system filter driver implement its semantics to replace the reparse point with the real file from auxiliary storage and complete the request. That is the stat() result I want when I say stat(filename, follow_symlinks=False) or lstat(filename), because this file is not a symlink. It's implicitly just the file to end users -- despite whatever backend tricks are being played in the kernel to implement other behavior such as HSM. Conflating this with a symlink is not right. Lies catch up with us. We can't copy it as link via os.symlink and os.readlink, and it doesn't get treated like a symlink in API functions.  

If you want to add an "open reparse point" parameter, that would make sense. It's of some use to get the tag and implement particular behavior for types of reparse points, and particularly for name surrogates, which includes mount points (junctions).

As to mount points, yes, I do think we should always traverse them. Please see my extended comment and the follow-up example on GitHub.

> Again, not sure why we'd want to hide the ability to manipulate the 
> junction itself from Python users, except to emulate POSIX. And I'd 
> imagine anyone using lstat() is doing it deliberately to manipulate 
> the link and would prefer we didn't force them to add Windows-
> specific code that's even more complex.

A mount point is not a link. ismount() and islink() can never both be true. Also, a POSIX symlink can never be a directory, which is why we make stat() pretend directory symlinks aren't directories. If the user wants a link, they can use a symlink that's created by os.symlink, mklink, new-item -type SymbolicLink, etc.