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>

Documentation/git-commit.txt

@@ -10,7 +10,7 @@ SYNOPSIS
 [verse]
 'git-commit' [-a | --interactive] [-s] [-v] [-u]
 	   [(-c | -C) <commit> | -F <file> | -m <msg> | --amend]
-	   [--no-verify] [-e] [--author <author>]
+	   [--allow-empty] [--no-verify] [-e] [--author <author>]
 	   [--] [[-i | -o ]<file>...]
 
 DESCRIPTION
@@ -89,6 +89,12 @@ OPTIONS
 	This option bypasses the pre-commit hook.
 	See also link:hooks.html[hooks].
 
+--allow-empty::
+	Usually recording a commit that has the exact same tree as its
+	sole parent commit and the command prevents you from making such
+	a mistake.  This option bypasses the safety, and is primarily
+	for use by foreign scm interface scripts.
+
 -e|--edit::
 	The message taken from file with `-F`, command line with
 	`-m`, and from file with `-C` are usually used as the

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"

t/t7501-commit.sh

@@ -256,6 +256,13 @@ test_expect_success 'same tree (single parent)' '
 
 '
 
+test_expect_success 'same tree (single parent) --allow-empty' '
+
+	git commit --allow-empty -m "forced empty" &&
+	git cat-file commit HEAD | grep forced
+
+'
+
 test_expect_success 'same tree (merge and amend merge)' '
 
 	git checkout -b side HEAD^ &&