from __future__ import absolute_import

from mercurial import (
    error,
    node,
)

from mercurial.i18n import _

def enforcesinglehead(repo, tr):
    for name, heads in repo.filtered('visible').branchmap().iteritems():
        if len(heads) > 1:
            hexs = [node.short(n) for n in heads]
            raise error.Abort(_('%d heads on "%s"') % (len(heads), name),
                              hint=(', '.join(hexs)))