This new command can be used to set symbolic marks for an commit while
doing a rebase. This symbolic name can later be used for merges or
resets.

The decision to use references for the marks and not files like done with
the rewritten commits for preserve merges was made to ensure no commit
objects get lost if prune is started while (a long term) rebase is
running. This also unifies the checking of the validity of marks and
references by using rev-parse for it.

The usage of : as the sign for marks conforms with the tag sign of
fast-export and fast-import.

Signed-off-by: Jörg Sommer <joerg@alea.gnuu.de>
---
 git-rebase--interactive.sh    |   37 ++++++++++++++++++++++++++++++++++++-
 t/t3404-rebase-interactive.sh |   17 +++++++++++++++++
 2 files changed, 53 insertions(+), 1 deletions(-)

diff --git a/git-rebase--interactive.sh b/git-rebase--interactive.sh
index 531ee94..6ac316a 100755
--- a/git-rebase--interactive.sh
+++ b/git-rebase--interactive.sh
@@ -35,6 +35,8 @@ mark the corrected paths with 'git add <paths>', and
 run 'git rebase --continue'"
 export GIT_CHERRY_PICK_HELP
 
+mark_prefix=refs/rebase-marks/
+
 warn () {
 	echo "$*" >&2
 }
@@ -105,7 +107,13 @@ die_with_patch () {
 }
 
 cleanup_before_quit () {
-	rm -rf "$DOTEST"
+	rm -rf "$DOTEST" &&
+	for ref in "$GIT_DIR/$mark_prefix"*
+	do
+		test "$ref" = "$GIT_DIR/$mark_prefix*" && continue
+		git update-ref -d "${ref#$GIT_DIR/}" "${ref#$GIT_DIR/}" || \
+			return 1
+	done
 }
 
 die_abort () {
@@ -244,6 +252,19 @@ peek_next_command () {
 	sed -n "1s/ .*$//p" < "$TODO"
 }
 
+mark_to_ref () {
+	case "$1" in
+	:[!/]*)
+		# :/SOMETHING is a reference for the last commit whose
+                # message starts with SOMETHING
+		echo "$mark_prefix${1#:}"
+		;;
+	*)
+		echo "$1"
+		;;
+	esac
+}
+
 do_next () {
 	rm -f "$DOTEST"/message "$DOTEST"/author-script \
 		"$DOTEST"/amend || exit
@@ -321,6 +342,15 @@ do_next () {
 			die_with_patch $sha1 ""
 		fi
 		;;
+	mark)
+		mark_action_done
+
+		mark=$(mark_to_ref :${sha1#:})
+		git rev-parse --verify "$mark" > /dev/null 2>&1 && \
+			warn "mark $sha1 already exist; overwriting it"
+
+		git update-ref "$mark" HEAD || die "update-ref failed"
+		;;
 	*)
 		warn "Unknown command: $command $sha1 $rest"
 		die_with_patch $sha1 "Please fix this in the file $TODO."
@@ -533,10 +563,15 @@ do
 
 # Rebase $SHORTUPSTREAM..$SHORTHEAD onto $SHORTONTO
 #
+# In the todo insn whenever you need to refer to a commit, in addition
+# to the usual commit object name, you can use ':mark' syntax to refer
+# to a commit previously marked with the 'mark' insn.
+#
 # Commands:
 #  pick = use commit
 #  edit = use commit, but stop for amending
 #  squash = use commit, but meld into previous commit
+#  mark :mark = mark the current HEAD for later reference
 #
 # If you remove a line here THAT COMMIT WILL BE LOST.
 # However, if you remove everything, the rebase will be aborted.
diff --git a/t/t3404-rebase-interactive.sh b/t/t3404-rebase-interactive.sh
index 8d29878..fa3560e 100755
--- a/t/t3404-rebase-interactive.sh
+++ b/t/t3404-rebase-interactive.sh
@@ -82,6 +82,9 @@ for line in $FAKE_LINES; do
 	case $line in
 	squash|edit)
 		action="$line";;
+	mark*)
+		echo "mark ${line#mark}"
+		echo "mark ${line#mark}" >> "$1";;
 	*)
 		echo sed -n "${line}s/^pick/$action/p"
 		sed -n "${line}p" < "$1".tmp
@@ -189,6 +192,20 @@ test_expect_success '-p handles "no changes" gracefully' '
 	test $HEAD = $(git rev-parse HEAD)
 '
 
+test_expect_success 'setting marks works' '
+	git checkout master &&
+	FAKE_LINES="mark:0 2 1 mark:42 3 edit 4" git rebase -i HEAD~4 &&
+	marks_dir=.git/refs/rebase-marks &&
+	test -d $marks_dir &&
+	test $(ls $marks_dir | wc -l) -eq 2 &&
+	test "$(git rev-parse HEAD~4)" = \
+		"$(git rev-parse refs/rebase-marks/0)" &&
+	test "$(git rev-parse HEAD~2)" = \
+		"$(git rev-parse refs/rebase-marks/42)" &&
+	git rebase --abort &&
+	ls $marks_dir | wc -l | grep -Fx 0
+'
+
 test_expect_success 'preserve merges with -p' '
 	git checkout -b to-be-preserved master^ &&
 	: > unrelated-file &&
-- 
1.5.5

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