from mercurial import revset

from mercurial import error

def ngtip(repo, branch, all=False):

    """tip new generation"""

    ## search for untopiced heads of branch

    # could be heads((::branch(x) - topic()))

    # but that is expensive

    #

    # we should write plain code instead

    subquery = '''heads(

                    parents(

                       ancestor(

                         (head() and branch(%s)

                         or (topic() and branch(%s)))))

                   ::(head() and branch(%s))

                   - topic())'''

    if not all:

        subquery = 'max(%s)' % subquery

    return repo.revs(subquery, branch, branch, branch)