config: teach the fetch.recurseSubmodules option the 'on-demand' value

To enable the user to change the default behavior of "git fetch" and "git
pull" regarding submodule recursion add the new "on-demand" value which
has just been added to the "--recurse-submodules" command line option.

Signed-off-by: Jens Lehmann <Jens.Lehmann@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/config.txt

@@ -900,9 +900,13 @@ diff.wordRegex::
 	characters are *ignorable* whitespace.
 
 fetch.recurseSubmodules::
-	A boolean value which changes the behavior for fetch and pull, the
-	default is to not recursively fetch populated submodules unless
-	configured otherwise.
+	This option can be either set to a boolean value or to 'on-demand'.
+	Setting it to a boolean changes the behavior of fetch and pull to
+	unconditionally recurse into submodules when set to true or to not
+	recurse at all when set to false. When set to 'on-demand' (the default
+	value), fetch and pull will only recurse into a populated submodule
+	when its superproject retrieves a commit that updates the submodule's
+	reference.
 
 fetch.unpackLimit::
 	If the number of objects fetched over the git native

submodule.c

@@ -71,7 +71,7 @@ int submodule_config(const char *var, const char *value, void *cb)
 	if (!prefixcmp(var, "submodule."))
 		return parse_submodule_config_option(var, value);
 	else if (!strcmp(var, "fetch.recursesubmodules")) {
-		config_fetch_recurse_submodules = git_config_bool(var, value);
+		config_fetch_recurse_submodules = parse_fetch_recurse_submodules_arg(var, value);
 		return 0;
 	}
 	return 0;

t/t5526-fetch-submodules.sh

@@ -372,4 +372,32 @@ test_expect_success "'--recurse-submodules=on-demand' stops when no new submodul
 	test_cmp expect.err.file actual.err
 '
 
+test_expect_success "'fetch.recurseSubmodules=on-demand' overrides global config" '
+	(
+		cd downstream &&
+		git fetch --recurse-submodules
+	) &&
+	add_upstream_commit &&
+	git config --global fetch.recurseSubmodules false &&
+	head1=$(git rev-parse --short HEAD) &&
+	git add submodule &&
+	git commit -m "new submodule" &&
+	head2=$(git rev-parse --short HEAD) &&
+	echo "From $pwd/." > expect.err.2 &&
+	echo "   $head1..$head2  master     -> origin/master" >> expect.err.2
+	head -2 expect.err >> expect.err.2 &&
+	(
+		cd downstream &&
+		git config fetch.recurseSubmodules on-demand &&
+		git fetch >../actual.out 2>../actual.err
+	) &&
+	git config --global --unset fetch.recurseSubmodules &&
+	(
+		cd downstream &&
+		git config --unset fetch.recurseSubmodules
+	) &&
+	test_cmp expect.out.sub actual.out &&
+	test_cmp expect.err.2 actual.err
+'
+
 test_done