setdiscovery: use revset for resolving DAG heads in a subset This was the final use of dagutil in setdiscovery! For reasons I didn't investigate, feeding a set with nullrev into the heads() revset resulted in a bunch of tests failing. Filtering out nullrev from the input set fixes things. Differential Revision: https://phab.mercurial-scm.org/D4324

dagutil: remove ability to invert instances The previous commit removed the last consumer of this feature. .. api:: remove inverse() methods from classes in dagutil Differential Revision: https://phab.mercurial-scm.org/D4323

setdiscovery: don't use dagutil for parent resolution _updatesample()'s one remaining use of revlogdag is for resolving the parents of a revision. In 2 cases, we actually resolve parents. In 1, we operate on the inverted DAG and resolve children. This commit teaches _updatesample() to receive an argument defining the function to resolve "parent" revisions. Call sites pass in changelog.parentrevs() or a wrapper around changelog.children() accordingly. The use of children() is semantically correct. But it is quadratic, since revlog.children() does a range scan over all revisions starting at its input and effectively calls parentrevs() to build up the list of children. So calling it repeatedly in a loop is a recipe for bad performance. I will be implementing something better in a subsequent commit. I wanted to get the porting off of dagutil done in a way that was simple and correct. Like other patches in this series, this change is potentially impacted but revlogdag's ignorance of filtered revisions. The new code is filtering aware, since changelog's revs() (used by children() will skip filtered revisions and therefore hidden children won't appear. This is potentially backwards incompatible. But no tests fail and I think this code should respect visibility. Differential Revision: https://phab.mercurial-scm.org/D4322

setdiscovery: use revsets for computing a subset's heads and roots revlogdag.headsetofconnecteds() obtains the set of DAG heads in a given set of revs. revlogdag.inverse() inverts the DAG order and makes headsetofconnecteds() obtain the DAG roots in a given subset. Both of these can be expressed with a revset. Like other patches in this series, revlogdag uses revlog.index and thus doesn't take filtering into account. Revsets do. So there is a chance for regressions with this change. But no tests fail. And I think this code should take filtering into account since hidden changesets shouldn't factor into discovery (unless operating on the hidden repository). Differential Revision: https://phab.mercurial-scm.org/D4321

dagutil: remove heads() and localsubset from revlogdag.__init__ The previous commit removed the last consumer of this API. I'm not going to mark as API incompatible because I doubt anybody used this functionality (outside of possibly passing an argument to revlogdag.__init__). I intend to remove revlogdag later in this series and its API annotation will cover this one. Differential Revision: https://phab.mercurial-scm.org/D4320

setdiscovery: pass head revisions into sample functions This eliminates the last remaining consumer of heads() and related functionality in dagutil. Differential Revision: https://phab.mercurial-scm.org/D4319

setdiscovery: pass heads into _updatesample() In preparation for eliminating the use of dagutil. Since _takefullsample() operates on the inverted DAG, it is easier to have the caller pass in the relevant set instead of teaching _updatesample() about when to invert the DAG. We keep the logic identical for now: future commits will remove dagutil. Differential Revision: https://phab.mercurial-scm.org/D4318