[PATCH 0/6] Let the sequencer handle `git rebase -i --root`

When I reimplemented the most performance-critical bits of the interactive rebase in the sequencer, to speed up `git rebase -i` particularly on Windows (even if the benefits are still quite notable on Linux or macOS), I punted on the --root part.

I had always hoped that some other contributor (or I myself) would come back later to address the --root part in the sequencer, too, with the idea that this would move the last remaining complicated code from git-rebase--interactive.sh into sequencer.c, to facilitate converting the rest of git-rebase--interactive.sh.

When I say "the last remaining complicated code", of course I neglect the --preserve-merges code, but as I worked hard on the --rebase-merges patch series with the intention to eventually deprecate and maybe even remove the --preserve-merges mode, I always implicitly assume that the --preserve-merges code will be moved into its own shell script (git-rebase--preserve-merges.sh, maybe?) and never be converted.

So here goes: the patches to move the handling of --root into the sequencer. After two preparatory patches, the real conversion takes place in the third patch. After that, we take care of the --root related concerns that arise in conjunction with the --rebase-merges mode.

As the --rebase-merges/--root patches overlap quite a bit (not so much in the code itself as in philosophical considerations such as "what should happen if you try to merge a branch into a new root", or the fact that the label/reset/merge commands make it desirable to be able to create a new root commit in the middle of a todo list), I had to consider in which order to contribute them. In the end, I decided to go with --rebase-merges first, so the --root patches are based on the --rebase-merges patch series.

I consider this patch series a critical prerequisite for Alban's Google Summer of Code project to convert rebase -i into a builtin.

Johannes Schindelin (6):
  sequencer: extract helper to update active_cache_tree
  sequencer: learn about the special "fake root commit" handling
  rebase -i --root: let the sequencer handle even the initial part
  sequencer: allow introducing new root commits
  rebase --rebase-merges: a "merge" into a new root is a fast-forward
  rebase --rebase-merges: root commits can be cousins, too

 git-rebase--interactive.sh        |   4 +-
 sequencer.c                       | 186 ++++++++++++++++++++++++++----
 sequencer.h                       |   4 +
 t/t3404-rebase-interactive.sh     |  19 ++-
 t/t3421-rebase-topology-linear.sh |   6 +-
 t/t3430-rebase-merges.sh          |  72 ++++++++++++
 6 files changed, 256 insertions(+), 35 deletions(-)

base-commit: 673fb9cb8b5c7d57cb560b6ade45e419c8dd09fc
Based-On: recreate-merges at https://github.com/dscho/git
Fetch-Base-Via: git fetch https://github.com/dscho/git recreate-merges
Published-As: https://github.com/dscho/git/releases/tag/sequencer-and-root-commits-v1
Fetch-It-Via: git fetch https://github.com/dscho/git sequencer-and-root-commits-v1