stablesort: record, cache and reuse jump Iterating below a merge means two things: 1) iterate over the part exclusive to the higher parents, 2) iterate from the lower parents. While iterating on the exclusive part, there will be case were we just go the next natural parent, and case were we'll have to "jump" to another revision. If we record all point this "jump" happens and their target, we can easily reproduce the iteration in the future. With that information we can iterate over the exclusive part of the merge without having to compute it entirely. In addition we store the reason of the jump. This will help the stable range processing later.

stablesort: fix head start computation The recursion was wrong and provided wrong result. As a side effect, this seems to hint that `stablesort_mergepoint_bounded` is not giving the right result for complex set.

stablesort: avoid attempting to sort a tuple This seems silly.

stablerange: use the filterparents utility

stablesort: use the filtered parents utility

depthcache: use parents filter in depth cache

parents: add a utility to filter parents There is various strange case of merge out there that needs to be handled. We add an utility function to handle them all.

stablerange: abstract the bit able to store cache into sql The part about actually storing the range is independent of the algorithm, so we should extract this before using it for the next iteration.

stablerange: split pure algorithm part from the on disk cache The stable cache file is getting long, we split the logic about keeping data on disk into a dedicated file.

stablerange: add an assert to detect buggy range Nothing can be negative in there, we add an assert to make sure it is so.

stablerange: warn cache for all relevant ancestors range Warming cache in the right order will prevent recursion to happens and unlock usage on large repository.

stablesort: move parent range computation into its own method Now that we have running code, we'll need to avoid too deep recursion. We extract the piece dealing with the parent range before we write more code to warm it.

stablerange: drop the basic inheritance from the 'mergepoint' version All necessary bits are implemented now (except for warmup which we explicitly bypass for now).

stablerange: cache known subrange at the stablerangecached level That way, the 'stablerange_mergepoint' class also benefit from it.