submodule: teach set-url subcommand

Currently, in the event that a submodule's upstream URL changes, users
have to manually alter the URL in the .gitmodules file then run
`git submodule sync`. Let's make that process easier.

Teach submodule the set-url subcommand which will automatically change
the `submodule.$name.url` property in the .gitmodules file and then run
`git submodule sync` to complete the process.

Signed-off-by: Denton Liu <liu.denton@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/git-submodule.sh b/git-submodule.sh
index c7f58c5..f7374dd 100755
--- a/git-submodule.sh
+++ b/git-submodule.sh
@@ -12,6 +12,7 @@
    or: $dashless [--quiet] deinit [-f|--force] (--all| [--] <path>...)
    or: $dashless [--quiet] update [--init] [--remote] [-N|--no-fetch] [-f|--force] [--checkout|--merge|--rebase] [--[no-]recommend-shallow] [--reference <repository>] [--recursive] [--] [<path>...]
    or: $dashless [--quiet] set-branch (--default|--branch <branch>) [--] <path>
+   or: $dashless [--quiet] set-url [--] <path> <newurl>
    or: $dashless [--quiet] summary [--cached|--files] [--summary-limit <n>] [commit] [--] [<path>...]
    or: $dashless [--quiet] foreach [--recursive] <command>
    or: $dashless [--quiet] sync [--recursive] [--] [<path>...]
@@ -761,6 +762,55 @@
 }
 
 #
+# Configures a submodule's remote url
+#
+# $@ = requested path, requested url
+#
+cmd_set_url() {
+	while test $# -ne 0
+	do
+		case "$1" in
+		-q|--quiet)
+			GIT_QUIET=1
+			;;
+		--)
+			shift
+			break
+			;;
+		-*)
+			usage
+			;;
+		*)
+			break
+			;;
+		esac
+		shift
+	done
+
+	if test $# -ne 2
+	then
+		usage
+	fi
+
+	# we can't use `git submodule--helper name` here because internally, it
+	# hashes the path so a trailing slash could lead to an unintentional no match
+	name="$(git submodule--helper list "$1" | cut -f2)"
+	if test -z "$name"
+	then
+		exit 1
+	fi
+
+	url="$2"
+	if test -z "$url"
+	then
+		exit 1
+	fi
+
+	git submodule--helper config submodule."$name".url "$url"
+	git submodule--helper sync ${GIT_QUIET:+--quiet} "$name"
+}
+
+#
 # Show commit summary for submodules in index or working tree
 #
 # If '--cached' is given, show summary between index and given commit,
@@ -1059,7 +1109,7 @@
 while test $# != 0 && test -z "$command"
 do
 	case "$1" in
-	add | foreach | init | deinit | update | set-branch | status | summary | sync | absorbgitdirs)
+	add | foreach | init | deinit | update | set-branch | set-url | status | summary | sync | absorbgitdirs)
 		command=$1
 		;;
 	-q|--quiet)