[PATCH v5 00/12] rebase -i: offer to recreate merge commits

Once upon a time, I dreamt of an interactive rebase that would not flatten branch structure, 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 --recreate-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 --recreate-merges.

Changes since v3:

- (sorry for the broken iteration v4)

- fixed a grammar error in "introduce the `merge` command"'s commit message.

- fixed a couple of resource leaks in safe_append() and do_reset(), pointed
  out by Eric Sunshine.

Johannes Schindelin (11):
  sequencer: avoid using errno clobbered by rollback_lock_file()
  sequencer: make rearrange_squash() a bit more obvious
  sequencer: introduce new commands to reset the revision
  sequencer: introduce the `merge` command
  sequencer: fast-forward merge commits, if possible
  rebase-helper --make-script: introduce a flag to recreate merges
  rebase: introduce the --recreate-merges option
  sequencer: make refs generated by the `label` command worktree-local
  sequencer: handle post-rewrite for merge commands
  pull: accept --rebase=recreate to recreate the branch topology
  rebase -i: introduce --recreate-merges=[no-]rebase-cousins

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

 Documentation/config.txt               |   8 +
 Documentation/git-pull.txt             |   5 +-
 Documentation/git-rebase.txt           |  14 +-
 builtin/pull.c                         |  14 +-
 builtin/rebase--helper.c               |  13 +-
 builtin/remote.c                       |   2 +
 contrib/completion/git-completion.bash |   4 +-
 git-rebase--interactive.sh             |  22 +-
 git-rebase.sh                          |  16 +
 refs.c                                 |   3 +-
 sequencer.c                            | 742 ++++++++++++++++++++++++++++++++-
 sequencer.h                            |   7 +
 t/t3430-rebase-recreate-merges.sh      | 208 +++++++++
 13 files changed, 1027 insertions(+), 31 deletions(-)
 create mode 100755 t/t3430-rebase-recreate-merges.sh

base-commit: e3a80781f5932f5fea12a49eb06f3ade4ed8945c
Published-As: https://github.com/dscho/git/releases/tag/recreate-merges-v5
Fetch-It-Via: git fetch https://github.com/dscho/git recreate-merges-v5

Interdiff vs v4:
 diff --git a/sequencer.c b/sequencer.c
 index 63ae71a7512..b2bf63029d4 100644
 --- a/sequencer.c
 +++ b/sequencer.c
 @@ -2514,14 +2514,17 @@ static int safe_append(const char *filename, const char *fmt, ...)
  
  	if (write_in_full(fd, buf.buf, buf.len) < 0) {
  		error_errno(_("could not write to '%s'"), filename);
 +		strbuf_release(&buf);
  		rollback_lock_file(&lock);
  		return -1;
  	}
  	if (commit_lock_file(&lock) < 0) {
 +		strbuf_release(&buf);
  		rollback_lock_file(&lock);
  		return error(_("failed to finalize '%s'"), filename);
  	}
  
 +	strbuf_release(&buf);
  	return 0;
  }
  
 @@ -2601,8 +2604,11 @@ static int do_reset(const char *name, int len, struct replay_opts *opts)
  	unpack_tree_opts.update = 1;
  	unpack_tree_opts.reset = 1;
  
 -	if (read_cache_unmerged())
 +	if (read_cache_unmerged()) {
 +		rollback_lock_file(&lock);
 +		strbuf_release(&ref_name);
  		return error_resolve_conflict(_(action_name(opts)));
 +	}
  
  	if (!fill_tree_descriptor(&desc, &oid)) {
  		error(_("failed to find tree of %s"), oid_to_hex(&oid));