def requiredsourcerequirements(repo):
    """Obtain requirements required to be present to upgrade a repo.

    An upgrade will not be allowed if the repository doesn't have the
    requirements returned by this function.
    """
    return {
        # Introduced in Mercurial 0.9.2.
        b'revlogv1',
        # Introduced in Mercurial 0.9.2.
        b'store',
    }