Junio, I think this is now ready for `next`. Thank you for your patience
and help with this.

Once upon a time, I dreamed of an interactive rebase that would not
linearize all patches and drop all merge commits, but instead recreate
the commit topology faithfully.

My original attempt was --preserve-merges, but that design was so
limited that I did not even enable it in interactive mode.

Subsequently, it *was* enabled in interactive mode, with the predictable
consequences: as the --preserve-merges design does not allow for
specifying the parents of merge commits explicitly, all the new commits'
parents are defined *implicitly* by the previous commit history, and
hence it is *not possible to even reorder commits*.

This design flaw cannot be fixed. Not without a complete re-design, at
least. This patch series offers such a re-design.

Think of --rebase-merges as "--preserve-merges done right". It
introduces new verbs for the todo list, `label`, `reset` and `merge`.
For a commit topology like this:

            A - B - C
              \   /
                D

the generated todo list would look like this:

            # branch D
            pick 0123 A
            label branch-point
            pick 1234 D
            label D

            reset branch-point
            pick 2345 B
            merge -C 3456 D # C

There are more patches in the pipeline, based on this patch series, but
left for later in the interest of reviewable patch series: one mini
series to use the sequencer even for `git rebase -i --root`, and another
one to add support for octopus merges to --rebase-merges. And then one
to allow for rebasing merge commits in a smarter way (this one will need
a bit more work, though, as it can result in very complicated, nested
merge conflicts *very* easily).

Changes since v7:

- Touched up all the documentation (it was a mistake to copy-edit the
  --preserve-merges description, for example).

- Disentangled the rescheduling of label/reset/merge from the one of the
  pick/fixup/squash code path (thanks Phillip!).

- When the merge failed, we now write out .git/rebase-merge/patch.

- An `exec git cherry-pick` or `exec git revert` will no longer mess
  with refs/rewritten/ in sequencer_remove_state() (d'oh....).

Johannes Schindelin (14):
  sequencer: avoid using errno clobbered by rollback_lock_file()
  sequencer: make rearrange_squash() a bit more obvious
  sequencer: refactor how original todo list lines are accessed
  sequencer: offer helpful advice when a command was rescheduled
  sequencer: introduce the `merge` command
  sequencer: fast-forward `merge` commands, if possible
  rebase-helper --make-script: introduce a flag to rebase merges
  rebase: introduce the --rebase-merges option
  sequencer: make refs generated by the `label` command worktree-local
  sequencer: handle post-rewrite for merge commands
  rebase --rebase-merges: avoid "empty merges"
  pull: accept --rebase=merges to recreate the branch topology
  rebase -i: introduce --rebase-merges=[no-]rebase-cousins
  rebase -i --rebase-merges: add a section to the man page

Phillip Wood (1):
  rebase --rebase-merges: add test for --keep-empty

Stefan Beller (1):
  git-rebase--interactive: clarify arguments

 Documentation/config.txt               |   8 +
 Documentation/git-pull.txt             |   6 +-
 Documentation/git-rebase.txt           | 160 ++++-
 builtin/pull.c                         |  14 +-
 builtin/rebase--helper.c               |  13 +-
 builtin/remote.c                       |  18 +-
 contrib/completion/git-completion.bash |   4 +-
 git-rebase--interactive.sh             |  22 +-
 git-rebase.sh                          |  16 +
 refs.c                                 |   3 +-
 sequencer.c                            | 891 +++++++++++++++++++++++--
 sequencer.h                            |   7 +
 t/t3421-rebase-topology-linear.sh      |   1 +
 t/t3430-rebase-merges.sh               | 244 +++++++
 14 files changed, 1347 insertions(+), 60 deletions(-)
 create mode 100755 t/t3430-rebase-merges.sh

base-commit: fe0a9eaf31dd0c349ae4308498c33a5c3794b293

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