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.

stablerange: use sort cache to build 'mergepoint' information Using the walk cache gives use a better complexity we need to scale. There are further improvement we could make, but this is a good first step.

stablesort: make the iteration from head available to all This will be useful for the stablerange code to work properly.

depth: fix compare mode for `debugdepth` The compare mode was broken for silly reasons.

memfilectx: changectx argument is not mandatory As changectx argument is now mandatory for memfilectx, add a compatibility layer to pass it when necessary. The commit that made the parament mandatory in core is 8a0cac20a1ad

branching: merge stable into default

amend: fix a typo in amend help text related to the extract option s/extra/extract/

topic: fix compatibility with 4.3 A compatibility fixes ended up being overlooked, we are bringing it back into the main branch.