revset: add 'only' revset Adds a only() revset that has two forms: only(<set>) is equivalent to "::<set> - ::(heads() - heads(<set>::))" only(<include>,<exclude>) is equivalent to "::<include> - ::<exclude>" On a large repo, this implementation can process/traverse 50,000 revs in 0.7 seconds, versus 4.2 seconds using "::<include> - ::<exclude>". This is useful for performing histedits on your branch: hg histedit -r 'first(only(.))' Or lifting branch foo off of branch bar: hg rebase -d @ -s 'only(foo, bar)' Or a variety of other uses.