revset: disable subset optimization for parents() and children() (issue2437) For the boolean operators, the subset optimization works by calculating the cheaper argument first, and passing the subset to the second argument to restrict the revision domain. This works well for filtering predicates. But parents() don't work like a filter: it may return revisions outside the specified set. So, combining it with boolean operators may easily yield incorrect results. For instance, for the following revision graph: 0 -- 1 the expression '0 and parents(1)' should evaluate as follows: 0 and parents(1) -> 0 and 0 -> 0 But since [0] is passed to parents() as a subset, we get instead: 0 and parents(1 and 0) -> 0 and parents([]) -> 0 and [] -> [] This also affects children(), p1() and p2(), for the same reasons. Predicates that call these (like heads()) are also affected. We work around this issue by ignoring the subset when propagating the call inside those predicates.