rebase: add and use git_rebase__interactive__preserve_merges

At the moment it's an exact copy of git_rebase__interactive except
the name has changed.

Signed-off-by: Wink Saville <wink@saville.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-rebase--interactive.sh

@@ -1058,3 +1058,111 @@ git_rebase__interactive () {
 
 	complete_action
 }
+
+git_rebase__interactive__preserve_merges () {
+	initiate_action "$action"
+	ret=$?
+	if test $ret = 0; then
+		return 0
+	fi
+
+	setup_reflog_action
+	init_basic_state
+
+	if test t = "$preserve_merges"
+	then
+		if test -z "$rebase_root"
+		then
+			mkdir "$rewritten" &&
+			for c in $(git merge-base --all $orig_head $upstream)
+			do
+				echo $onto > "$rewritten"/$c ||
+					die "$(gettext "Could not init rewritten commits")"
+			done
+		else
+			mkdir "$rewritten" &&
+			echo $onto > "$rewritten"/root ||
+				die "$(gettext "Could not init rewritten commits")"
+		fi
+		# No cherry-pick because our first pass is to determine
+		# parents to rewrite and skipping dropped commits would
+		# prematurely end our probe
+		merges_option=
+	else
+		merges_option="--no-merges --cherry-pick"
+	fi
+
+	init_revisions_and_shortrevisions
+
+	if test t != "$preserve_merges"
+	then
+		git rebase--helper --make-script ${keep_empty:+--keep-empty} \
+			$revisions ${restrict_revision+^$restrict_revision} >"$todo" ||
+		die "$(gettext "Could not generate todo list")"
+	else
+		format=$(git config --get rebase.instructionFormat)
+		# the 'rev-list .. | sed' requires %m to parse; the instruction requires %H to parse
+		git rev-list $merges_option --format="%m%H ${format:-%s}" \
+			--reverse --left-right --topo-order \
+			$revisions ${restrict_revision+^$restrict_revision} | \
+			sed -n "s/^>//p" |
+		while read -r sha1 rest
+		do
+
+			if test -z "$keep_empty" && is_empty_commit $sha1 && ! is_merge_commit $sha1
+			then
+				comment_out="$comment_char "
+			else
+				comment_out=
+			fi
+
+			if test -z "$rebase_root"
+			then
+				preserve=t
+				for p in $(git rev-list --parents -1 $sha1 | cut -d' ' -s -f2-)
+				do
+					if test -f "$rewritten"/$p
+					then
+						preserve=f
+					fi
+				done
+			else
+				preserve=f
+			fi
+			if test f = "$preserve"
+			then
+				touch "$rewritten"/$sha1
+				printf '%s\n' "${comment_out}pick $sha1 $rest" >>"$todo"
+			fi
+		done
+	fi
+
+	# Watch for commits that been dropped by --cherry-pick
+	if test t = "$preserve_merges"
+	then
+		mkdir "$dropped"
+		# Save all non-cherry-picked changes
+		git rev-list $revisions --left-right --cherry-pick | \
+			sed -n "s/^>//p" > "$state_dir"/not-cherry-picks
+		# Now all commits and note which ones are missing in
+		# not-cherry-picks and hence being dropped
+		git rev-list $revisions |
+		while read rev
+		do
+			if test -f "$rewritten"/$rev &&
+			   ! sane_grep "$rev" "$state_dir"/not-cherry-picks >/dev/null
+			then
+				# Use -f2 because if rev-list is telling us this commit is
+				# not worthwhile, we don't want to track its multiple heads,
+				# just the history of its first-parent for others that will
+				# be rebasing on top of it
+				git rev-list --parents -1 $rev | cut -d' ' -s -f2 > "$dropped"/$rev
+				sha1=$(git rev-list -1 $rev)
+				sane_grep -v "^[a-z][a-z]* $sha1" <"$todo" > "${todo}2" ; mv "${todo}2" "$todo"
+				rm "$rewritten"/$rev
+			fi
+		done
+	fi
+
+	complete_action
+}

git-rebase.sh

@@ -197,7 +197,7 @@ run_specific_rebase () {
 		autosquash=
 	fi
 	. git-rebase--$type
-	git_rebase__$type
+	git_rebase__$type${preserve_merges:+__preserve_merges}
 	ret=$?
 	if test $ret -eq 0
 	then