We currently don't support symlinks on Windows (in fact, the project doesn't even build on Windows because of that). The advice I got from augie@google.com and former hg contributor "bmp" was (please correct me if I'm wrong):

• Prior to Windows 10: No symlink support
• Windows 10 without dev mode: No symlink support
• Windows 10 dev mode: use FFI to call CreateSymbolicLink
• Don't use the symlink creates, because it creates "junctions", which is not what we want.

Rust's standard library has std::os::windows::fs::symlink_file and std::os::windows::fs::symlink_dir, which both seem to call CreateSymbolicLinkW, only with different flags. Perhaps we can always use the symlink_file version? It's still unclear to me what the effect would be if a "file symbolic link" points to a target that's actually a directory.