setdiscovery: use a revset for finding DAG heads in a subset The march towards moving away from dagutil continues. Like other patches moving us away from dagutil, there is the potential for regressions to occur because revlogdag's headsetofconnecteds() uses revlog.index, which doesn't take filtering into account. The revset layer does. But no tests fail, so we appear to be in the clear. Differential Revision: https://phab.mercurial-scm.org/D4317

setdiscovery: reflect use of revs instead of nodes This code all operates on revision numbers. Update variable names and comments accordingly. Differential Revision: https://phab.mercurial-scm.org/D4316

dagutil: remove descendantset() and ancestorset() descendantset() is unused after the previous commit. And ancestorset() was only used by descendantset(), so it can be removed as well. .. api:: descendantset() and ancestorset() removed from dagutil Use a revset instead when operating on the changelog. Or use various functionality in the ancestor or dagop modules. Differential Revision: https://phab.mercurial-scm.org/D4315

setdiscovery: use a revset instead of dagutil.descendantset() This is the only use of descendantset() in the repo. Strictly speaking, the revset behaves slightly differently than dagutil. The reason is that dagutil is using revlog.index for DAG traversal and this data structure isn't aware of visibility / filtering. So it can operate on revisions it shouldn't operate on. But our test coverage of this code is pretty comprehensive and this change causes no tests to fail. So I think we are good. Also, the revset parser failed to parse `%ld:: - %ld::`, hence the use of descendants(). I'm not sure if that is a feature or a bug. Differential Revision: https://phab.mercurial-scm.org/D4314

setdiscovery: don't use dagutil to compute heads This is a relatively trivial operation to perform. We don't need to use dagutil. This brings us one step closer to eliminating dagutil. We still need to populate the heads on revlogdag because later functionality relies on it. Differential Revision: https://phab.mercurial-scm.org/D4310

dagutil: remove nodeset() AFAICT this was unused since the code was introduced by cb98fed52495 in 2011! Differential Revision: https://phab.mercurial-scm.org/D4309