git submodule summary: add --files option

index 7dd73ae..145802a 100644
@@ -15,7 +15,7 @@ SYNOPSIS
 'git submodule' [--quiet] init [--] [<path>...]
 'git submodule' [--quiet] update [--init] [-N|--no-fetch] [--rebase]
 	      [--reference <repository>] [--merge] [--] [<path>...]
-'git submodule' [--quiet] summary [--cached] [--summary-limit <n>] [commit] [--] [<path>...]
+'git submodule' [--quiet] summary [--cached|--files] [--summary-limit <n>] [commit] [--] [<path>...]
 'git submodule' [--quiet] foreach <command>
 'git submodule' [--quiet] sync [--] [<path>...]
 

@@ -127,7 +127,11 @@ summary::
 	Show commit summary between the given commit (defaults to HEAD) and
 	working tree/index. For a submodule in question, a series of commits
 	in the submodule between the given super project commit and the
-	index or working tree (switched by --cached) are shown.
+	index or working tree (switched by --cached) are shown. If the option
+	--files is given, show the series of commits in the submodule between
+	the index of super project the and the working tree of the submodule
+	(this option doesn't allow to use the --cached option or to provide an
+	explicit commit).
 
 foreach::
 	Evaluates an arbitrary shell command in each checked out submodule.

@@ -169,6 +173,11 @@ OPTIONS
 	commands typically use the commit found in the submodule HEAD, but
 	with this option, the commit stored in the index is used instead.
 
+--files::
+	This option is only valid for the summary command. This command
+	compares the commit in the index with that in the submodule HEAD
+	when this option is used.
+
 -n::
 --summary-limit::
 	This option is only valid for the summary command.

index ebed711..9bdd6ea 100755
@@ -4,7 +4,7 @@
 #
 # Copyright (c) 2007 Lars Hjemli
 
-USAGE="[--quiet] [--cached] \
+USAGE="[--quiet] [--cached|--files] \
 [add [-b branch] <repo> <path>]|[status|init|update [-i|--init] [-N|--no-fetch] [--rebase|--merge]|summary [-n|--summary-limit <n>] [<commit>]] \
 [--] [<path>...]|[foreach <command>]|[sync [--] [<path>...]]"
 OPTIONS_SPEC=

@@ -16,6 +16,7 @@ command=
 branch=
 reference=
 cached=
+files=
 nofetch=
 update=
 

@@ -460,6 +461,7 @@ set_name_rev () {
 cmd_summary() {
 	summary_limit=-1
 	for_status=
+	diff_cmd=diff-index
 
 	# parse $args after "submodule ... summary".
 	while test $# -ne 0

@@ -468,6 +470,9 @@ cmd_summary() {
 		--cached)
 			cached="$1"
 			;;
+		--files)
+			files="$1"
+			;;
 		--for-status)
 			for_status="$1"
 			;;

@@ -504,9 +509,17 @@ cmd_summary() {
 		head=HEAD
 	fi
 
+	if [ -n "$files" ]
+	then
+		test -n "$cached" &&
+		die "--cached cannot be used with --files"
+		diff_cmd=diff-files
+		head=
+	fi
+
 	cd_to_toplevel
 	# Get modified modules cared by user
-	modules=$(git diff-index $cached --raw $head -- "$@" |
+	modules=$(git $diff_cmd $cached --raw $head -- "$@" |
 		egrep '^:([0-7]* )?160000' |
 		while read mod_src mod_dst sha1_src sha1_dst status name
 		do

@@ -520,7 +533,7 @@ cmd_summary() {
 
 	test -z "$modules" && return
 
-	git diff-index $cached --raw $head -- $modules |
+	git $diff_cmd $cached --raw $head -- $modules |
 	egrep '^:([0-7]* )?160000' |
 	cut -c2- |
 	while read mod_src mod_dst sha1_src sha1_dst status name

index 6149829..6cc16c3 100755
@@ -56,6 +56,15 @@ test_expect_success 'modified submodule(forward)' "
 EOF
 "
 
+test_expect_success 'modified submodule(forward), --files' "
+	git submodule summary --files >actual &&
+	diff actual - <<-EOF
+* sm1 $head1...$head2 (1):
+  > Add foo3
+
+EOF
+"
+
 commit_file sm1 &&
 cd sm1 &&
 git reset --hard HEAD~2 >/dev/null &&

@@ -114,6 +123,15 @@ test_expect_success 'typechanged submodule(submodule->blob), --cached' "
 EOF
 "
 
+test_expect_success 'typechanged submodule(submodule->blob), --files' "
+    git submodule summary --files >actual &&
+    diff actual - <<-EOF
+* sm1 $head5(blob)->$head4(submodule) (3):
+  > Add foo5
+
+EOF
+"
+
 rm -rf sm1 &&
 git checkout-index sm1
 test_expect_success 'typechanged submodule(submodule->blob)' "

@@ -205,4 +223,8 @@ test_expect_success '--for-status' "
 EOF
 "
 
+test_expect_success 'fail when using --files together with --cached' "
+    test_must_fail git submodule summary --files --cached
+"
+
 test_done

@@ -129,7 +129,7 @@ summary::
        in the submodule between the given super project commit and the
        index or working tree (switched by --cached) are shown. If the option
        --files is given, show the series of commits in the submodule between
-       the index of super project the and the working tree of the submodule
+       the index of the super project and the working tree of the submodule
        (this option doesn't allow to use the --cached option or to provide an
        explicit commit).