submodule: add --no-fetch parameter to update command

git submodule update --no-fetch makes it possible to use git submodule
update in complete offline mode by not fetching new revisions.

This does make sense in the following setup:

* There is an unstable and a stable branch in the super/master repository.
* The submodules might be at different revisions in the branches.
* You are at some place without internet connection ;)

With this patch it is now possible to change branches and update
the submodules to be at the recorded revision without online access.

Another advantage is that with -N the update operation is faster, because fetch is checking for new updates even if there was no fetch/pull on the super/master repository since the last update.

Signed-off-by: Fabian Franz <git@fabian-franz.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-submodule.txt

@@ -12,7 +12,7 @@ SYNOPSIS
 'git submodule' [--quiet] add [-b branch] [--] <repository> <path>
 'git submodule' [--quiet] status [--cached] [--] [<path>...]
 'git submodule' [--quiet] init [--] [<path>...]
-'git submodule' [--quiet] update [--init] [--] [<path>...]
+'git submodule' [--quiet] update [--init] [-N|--no-fetch] [--] [<path>...]
 'git submodule' [--quiet] summary [--summary-limit <n>] [commit] [--] [<path>...]
 'git submodule' [--quiet] foreach <command>
 'git submodule' [--quiet] sync [--] [<path>...]
@@ -172,6 +172,11 @@ OPTIONS
 	(the default). This limit only applies to modified submodules. The
 	size is always limited to 1 for added/deleted/typechanged submodules.
 
+-N::
+--no-fetch::
+	This option is only valid for the update command.
+	Don't fetch new objects from the remote site.
+
 <path>...::
 	Paths to submodule(s). When specified this will restrict the command
 	to only operate on the submodules found at the specified paths.

git-submodule.sh

@@ -5,7 +5,7 @@
 # Copyright (c) 2007 Lars Hjemli
 
 USAGE="[--quiet] [--cached] \
-[add <repo> [-b branch] <path>]|[status|init|update [-i|--init]|summary [-n|--summary-limit <n>] [<commit>]] \
+[add <repo> [-b branch] <path>]|[status|init|update [-i|--init] [-N|--no-fetch]|summary [-n|--summary-limit <n>] [<commit>]] \
 [--] [<path>...]|[foreach <command>]|[sync [--] [<path>...]]"
 OPTIONS_SPEC=
 . git-sh-setup
@@ -16,6 +16,7 @@ command=
 branch=
 quiet=
 cached=
+nofetch=
 
 #
 # print stuff on stdout unless -q was specified
@@ -300,6 +301,10 @@ cmd_update()
 			shift
 			cmd_init "$@" || return
 			;;
+		-N|--no-fetch)
+			shift
+			nofetch=1
+			;;
 		--)
 			shift
 			break
@@ -345,8 +350,16 @@ cmd_update()
 			then
 				force="-f"
 			fi
-			(unset GIT_DIR; cd "$path" && git-fetch &&
-				git-checkout $force -q "$sha1") ||
+
+			if test -z "$nofetch"
+			then
+				(unset GIT_DIR; cd "$path" &&
+					git-fetch) ||
+				die "Unable to fetch in submodule path '$path'"
+			fi
+
+			(unset GIT_DIR; cd "$path" &&
+				  git-checkout $force -q "$sha1") ||
 			die "Unable to checkout '$sha1' in submodule path '$path'"
 
 			say "Submodule path '$path': checked out '$sha1'"