1538
1539
:returns: One of: 'a_descends_from_b', 'b_descends_from_a', 'diverged'
1540
1541
heads = graph.heads([revision_a, revision_b])
1542
1543
return 'b_descends_from_a'
1544
1545
# These branches have diverged
1547
1548
return 'a_descends_from_b'
1549
1550
raise AssertionError("invalid heads: %r" % (heads,))