delta-find: explicitly deal with usage of the cached revision We can remove this from the general logic path and directly deal with this corner case early. This result in a small change in test-generaldelta.t as it turns out that: - at commit time we (sometimes) precompute a delta against p1 and pass it as the cached delta. - since cached delta where going through the same filtering as everything, we could "optimize" the base if it applied to an empty delta, resulting in not using the pre-computed delta. The simpler logic fix the second item, making the cached delta base always actually tested when requested. Note that the computation of a fast delta against p1 only is questionable, but looking into that is out of scope for this series.

delta-find: remove the "candidate groups" layer We have enough pieces to remove this generator and directly bear it load using the underlying object.

delta-find: stop using heuristic to determine if we are creating a snapshot This avoid assuming a changeset is a snapshot when it is actually something simpler.

delta-find: explicitly track stage of the search Being more explicit about what we are doing is going to be useful. We actually start making use of it in later changesets.

delta-find: drop some dead debug code Seems like it was never put to use, so lets simply remove it for now.

delta-find: introduce and use specialized _DeltaSearch class For now, we introduce some very simple variant, but they are still useful to display how having the class can helps keeping the simple case simple and their special case out of more advanced logic.

delta-find: introduce a base class for _DeltaSearch This prepare the introduction of specialized the class in the next changesets.

delta-find: simplify the delta checking function for snapshot Since the function is all about snapshot, we can safely use an early return and make the result simpler.

delta-find: move good delta code earlier in the class Nothing change except the code location. This greatly helps readability of the next future diff,

delta-find: split is_good_delta_info into more thematic function Same logic as for candidate filtering, we group code into related sub method. This will help clarifying later patches as some logic is pre-splitted