git-commit --allow-empty

It does not usually make sense to record a commit that has the exact
same tree as its sole parent commit and that is why git-commit prevents
you from making such a mistake, but when data from foreign scm is
involved, it is a different story.  We are equipped to represent such an
(perhaps insane, perhaps by mistake, or perhaps done on purpose) empty
change, and it is better to represent it bypassing the safety valve for
native use.

This is primarily for use by foreign scm interface scripts.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-commit.sh

@@ -74,6 +74,7 @@ trap '
 
 all=
 also=
+allow_empty=f
 interactive=
 only=
 logfile=
@@ -114,6 +115,10 @@ do
 	-a|--a|--al|--all)
 		all=t
 		;;
+	--allo|--allow|--allow-|--allow-e|--allow-em|--allow-emp|\
+	--allow-empt|--allow-empty)
+		allow_empty=t
+		;;
 	--au=*|--aut=*|--auth=*|--autho=*|--author=*)
 		force_author="${1#*=}"
 		;;
@@ -515,9 +520,11 @@ else
 	# we need to check if there is anything to commit
 	run_status >/dev/null
 fi
-case "$?,$PARENTS" in
-0,* | *,-p' '?*-p' '?*)
-	# a merge commit can record the same tree as its parent.
+case "$allow_empty,$?,$PARENTS" in
+t,* | ?,0,* | ?,*,-p' '?*-p' '?*)
+	# an explicit --allow-empty, or a merge commit can record the
+	# same tree as its parent.  Otherwise having commitable paths
+	# is required.
 	;;
 *)
 	rm -f "$GIT_DIR/COMMIT_EDITMSG" "$GIT_DIR/SQUASH_MSG"