Re: [PATCH 3/6] rebase -i --root: let the sequencer handle even the initial part

> In this developer's earlier attempt to accelerate interactive rebases by
> converting large parts from Unix shell script into portable, performant
> C, the --root handling was specifically excluded (to simplify the task a
> little bit; it still took over a year to get that reduced set of patches
> into Git proper).
>
> This patch ties up that loose end: now only --preserve-merges uses the
> slow Unix shell script implementation to perform the interactive rebase.
>
> As the rebase--helper reports progress to stderr (unlike the scripted
> interactive rebase, which reports it to stdout, of all places), we have
> to adjust a couple of tests that did not expect that for `git rebase -i
> --root`.
>
> This patch fixes -- at long last! -- the really old bug reported in
> 6a6bc5bdc4d (add tests for rebasing root, 2013-06-06) that rebasing with
> --root *always* rewrote the root commit, even if there were no changes.
>
> The bug still persists in --preserve-merges mode, of course, but that
> mode will be deprecated as soon as the new --rebase-merges mode
> stabilizes, anyway.
>
> Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
> ---
>  git-rebase--interactive.sh        |  4 +++-
>  t/t3404-rebase-interactive.sh     | 19 +++++++++++++------
>  t/t3421-rebase-topology-linear.sh |  6 +++---
>  3 files changed, 19 insertions(+), 10 deletions(-)
>
> diff --git a/git-rebase--interactive.sh b/git-rebase--interactive.sh
> index cbf44f86482..2f4941d0fc9 100644
> --- a/git-rebase--interactive.sh
> +++ b/git-rebase--interactive.sh
> @@ -894,6 +894,8 @@ init_revisions_and_shortrevisions () {
>         else
>                 revisions=$onto...$orig_head
>                 shortrevisions=$shorthead
> +               test -z "$squash_onto" ||
> +               echo "$squash_onto" >"$state_dir"/squash-onto
>         fi
>  }
>
> @@ -948,7 +950,7 @@ EOF
>         die "Could not skip unnecessary pick commands"
>
>         checkout_onto
> -       if test -z "$rebase_root" && test ! -d "$rewritten"
> +       if test ! -d "$rewritten"