view CONTRIBUTING @ 32903:27932a76a88d

dagop: split module hosting DAG-related algorithms from revset

This module hosts the following functions. They are somewhat similar (e.g.
scanning revisions using heap queue or stack) and seem non-trivial in
algorithmic point of view.

 - _revancestors()
 - _revdescendants()
 - reachableroots()
 - _toposort()

I was thinking of adding revset._fileancestors() generator for better follow()
implementation, but it would be called from context.py as well. So I decided
to create new module.

Naming is hard. I couldn't come up with any better module name, so it's called
"dag operation" now. I rejected the following candidates:

 - ancestor.py - existing, revlog-level DAG algorithm
 - ancestorset.py - doesn't always return a set
 - dagalgorithm.py - hard to type
 - dagutil.py - existing
 - revancestor.py - I want to add fileancestors()

  % wc -l mercurial/dagop.py mercurial/revset.py
    339 mercurial/dagop.py
   2020 mercurial/revset.py
   2359 total

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