RemoteLOCAL.unprotect modifies cache permissions for symlinked files

[danfischetti]

Please provide information about your setup
dvc --version 0.91.1

The RemoteLOCAL.unprotect function for an output tries to replace the symlink with a copy of the data. First the cache file is copied to a tmp dir, then the link is removed, then the tmp file is renamed. The problem is with the remove function defined here:

def remove(path):
    logger.debug("Removing '%s'", path)    path = fspath_py35(path)
    try:
        if os.path.isdir(path):
            shutil.rmtree(path, onerror=_chmod)
        else:
            _chmod(os.unlink, path, None)
    except OSError as exc:
        if exc.errno != errno.ENOENT:
            raise

It calls _chmod on the link path, defined here

def _chmod(func, p, excinfo):
    perm = os.lstat(p).st_mode
    perm |= stat.S_IWRITE    try:
        os.chmod(p, perm)
    except OSError as exc:
        # broken symlink or file is not owned by us
        if exc.errno not in [errno.ENOENT, errno.EPERM]:
            raise    func(p)

but this call os.chmod(p, perm) changes the permissions of the cached file, not the link.