submodule--helper: set alternateLocation for cloned submodules

In 31224cb (clone: recursive and reference option triggers
submodule alternates, 2016-08-17) a mechanism was added to
have submodules referenced.  It did not address _nested_
submodules, however.

This patch makes all not just the root repository, but also
all submodules (recursively) have submodule.alternateLocation
and submodule.alternateErrorStrategy configured, making Git
search for possible alternates for nested submodules as well.

As submodule's alternate target does not end in .git/objects
(rather .git/modules/qqqqqq/objects), this alternate target
path restriction for in add_possible_reference_from_superproject
relates from "*.git/objects" to just */objects".

New tests have been added to t7408-submodule-reference.

Signed-off-by: Vitaly _Vi Shukela <vi0oss@gmail.com>
Reviewed-by: Stefan Beller <sbeller@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: vi

builtin/submodule--helper.c

@@ -498,9 +498,9 @@ static int add_possible_reference_from_superproject(
 
 	/*
 	 * If the alternate object store is another repository, try the
-	 * standard layout with .git/modules/<name>/objects
+	 * standard layout with .git/(modules/<name>)+/objects
 	 */
-	if (ends_with(alt->path, ".git/objects")) {
+	if (ends_with(alt->path, "/objects")) {
 		char *sm_alternate;
 		struct strbuf sb = STRBUF_INIT;
 		struct strbuf err = STRBUF_INIT;
@@ -583,6 +583,7 @@ static int module_clone(int argc, const char **argv, const char *prefix)
 	struct strbuf rel_path = STRBUF_INIT;
 	struct strbuf sb = STRBUF_INIT;
 	struct string_list reference = STRING_LIST_INIT_NODUP;
+	char *sm_alternate = NULL, *error_strategy = NULL;
 
 	struct option module_clone_options[] = {
 		OPT_STRING(0, "prefix", &prefix,
@@ -672,6 +673,20 @@ static int module_clone(int argc, const char **argv, const char *prefix)
 		die(_("could not get submodule directory for '%s'"), path);
 	git_config_set_in_file(p, "core.worktree",
 			       relative_path(path, sm_gitdir, &rel_path));
+
+	/* setup alternateLocation and alternateErrorStrategy in the cloned submodule if needed */
+	git_config_get_string("submodule.alternateLocation", &sm_alternate);
+	if (sm_alternate)
+		git_config_set_in_file(p, "submodule.alternateLocation",
+					   sm_alternate);
+	git_config_get_string("submodule.alternateErrorStrategy", &error_strategy);
+	if (error_strategy)
+		git_config_set_in_file(p, "submodule.alternateErrorStrategy",
+					   error_strategy);
+
+	free(sm_alternate);
+	free(error_strategy);
+
 	strbuf_release(&sb);
 	strbuf_release(&rel_path);
 	free(sm_gitdir);

t/t7408-submodule-reference.sh

@@ -125,4 +125,70 @@ test_expect_success 'ignoring missing submodule alternates passes clone and subm
 	)
 '
 
+test_expect_success 'preparing second superproject with a nested submodule plus partial clone' '
+	test_create_repo supersuper &&
+	(
+		cd supersuper &&
+		echo "I am super super." >file &&
+		git add file &&
+		git commit -m B-super-super-initial
+		git submodule add "file://$base_dir/super" subwithsub &&
+		git commit -m B-super-super-added &&
+		git submodule update --init --recursive &&
+		git repack -ad
+	) &&
+	git clone supersuper supersuper2 &&
+	(
+		cd supersuper2 &&
+		git submodule update --init
+	)
+'
+
+# At this point there are three root-level positories: A, B, super and super2
+
+test_expect_success 'nested submodule alternate in works and is actually used' '
+	test_when_finished "rm -rf supersuper-clone" &&
+	git clone --recursive --reference supersuper supersuper supersuper-clone &&
+	(
+		cd supersuper-clone &&
+		# test superproject has alternates setup correctly
+		test_alternate_is_used .git/objects/info/alternates . &&
+		# immediate submodule has alternate:
+		test_alternate_is_used .git/modules/subwithsub/objects/info/alternates subwithsub &&
+		# nested submodule also has alternate:
+		test_alternate_is_used .git/modules/subwithsub/modules/sub/objects/info/alternates subwithsub/sub
+	)
+'
+
+check_that_two_of_three_alternates_are_used() {
+	test_alternate_is_used .git/objects/info/alternates . &&
+	# immediate submodule has alternate:
+	test_alternate_is_used .git/modules/subwithsub/objects/info/alternates subwithsub &&
+	# but nested submodule has no alternate:
+	test_must_fail test_alternate_is_used .git/modules/subwithsub/modules/sub/objects/info/alternates subwithsub/sub
+}
+
+
+test_expect_success 'missing nested submodule alternate fails clone and submodule update' '
+	test_when_finished "rm -rf supersuper-clone" &&
+	test_must_fail git clone --recursive --reference supersuper2 supersuper2 supersuper-clone &&
+	(
+		cd supersuper-clone &&
+		check_that_two_of_three_alternates_are_used &&
+		# update of the submodule fails
+		test_must_fail git submodule update --init --recursive
+	)
+'
+
+test_expect_success 'missing nested submodule alternate in --reference-if-able mode' '
+	test_when_finished "rm -rf supersuper-clone" &&
+	git clone --recursive --reference-if-able supersuper2 supersuper2 supersuper-clone &&
+	(
+		cd supersuper-clone &&
+		check_that_two_of_three_alternates_are_used &&
+		# update of the submodule succeeds
+		git submodule update --init --recursive
+	)
+'
+
 test_done