[PATCH] rebase -i: avoid --cherry-pick when rebasing to a direct ancestor

[Thomas Rast <trast@student.ethz.ch>]

Ordinary 'rebase -i' reads the commits to rebase with (roughly)

  git rev-list --left-right --cherry-pick $upstream...

which gives it the feature of skipping commits that are already
present in $upstream.  However, in the common use-case of rewriting a
few commits up to an ancestor, as in 'git rebase -i HEAD~3', the
--cherry-pick is useless since there are no commits to compare to.

Add a check if $upstream is a direct ancestor of HEAD, and leave away
the --cherry-pick if so.  Since the --cherry-pick is already in
$MERGES_OPTION, we need to decide this before setting the latter.

For simplicity we skip --root mode.  In theory we could do the same
optimization, but using --root --onto <ancestor> is probably even more
rare than having performance issues with --cherry-pick.

Signed-off-by: Thomas Rast <trast@student.ethz.ch>
---

The --cherry-pick mechanism itself could get a similar optimization,
but I don't know that code.


 git-rebase--interactive.sh |    7 ++++++-
 1 files changed, 6 insertions(+), 1 deletions(-)

diff --git a/git-rebase--interactive.sh b/git-rebase--interactive.sh
index 1fda620..10b0ed8 100755
--- a/git-rebase--interactive.sh
+++ b/git-rebase--interactive.sh
@@ -870,7 +870,12 @@ first and then run 'git rebase --continue' again."
 			MERGES_OPTION=
 			first_after_upstream="$(git rev-list --reverse --first-parent $UPSTREAM..$HEAD | head -n 1)"
 		else
-			MERGES_OPTION="--no-merges --cherry-pick"
+			if test -z "$REBASE_ROOT" &&
+				test $(git merge-base $UPSTREAM $HEAD) = $UPSTREAM; then
+				MERGES_OPTION="--no-merges"
+			else
+				MERGES_OPTION="--no-merges --cherry-pick"
+			fi
 		fi
 
 		SHORTHEAD=$(git rev-parse --short $HEAD)
-- 
1.7.0.139.gd1a75