submodules: fix of regression on fetching of non-init subsub-repo

A regression has been introduced by a62387b (submodule.c: fetch in
submodules git directory instead of in worktree, 2018-11-28).

The scenario in which it triggers is when one has a remote repository
with a subrepository inside a subrepository like this:
superproject/middle_repo/inner_repo

Person A and B have both a clone of it, while Person B is not working
with the inner_repo and thus does not have it initialized in his working
copy.

Now person A introduces a change to the inner_repo and propagates it
through the middle_repo and the superproject.

Once person A pushed the changes and person B wants to fetch them using
"git fetch" on superproject level, B's git call will return with error
saying:

Could not access submodule 'inner_repo'
Errors during submodule fetch:
         middle_repo

Expectation is that in this case the inner submodule will be recognized
as uninitialized subrepository and skipped by the git fetch command.

This used to work correctly before 'a62387b (submodule.c: fetch in
submodules git directory instead of in worktree, 2018-11-28)'.

Starting with a62387b the code wants to evaluate "is_empty_dir()" inside
.git/modules for a directory only existing in the worktree, delivering
then of course wrong return value.

This patch reverts the changes of a62387b and introduces a regression
test.

Signed-off-by: Peter Kaestle <peter.kaestle@nokia.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

submodule.c

@@ -499,12 +499,6 @@ void prepare_submodule_repo_env(struct strvec *out)
 		     DEFAULT_GIT_DIR_ENVIRONMENT);
 }
 
-static void prepare_submodule_repo_env_in_gitdir(struct strvec *out)
-{
-	prepare_submodule_repo_env_no_git_dir(out);
-	strvec_pushf(out, "%s=.", GIT_DIR_ENVIRONMENT);
-}
-
 /*
  * Initialize a repository struct for a submodule based on the provided 'path'.
  *
@@ -1455,8 +1449,8 @@ static int get_next_submodule(struct child_process *cp,
 		if (task->repo) {
 			struct strbuf submodule_prefix = STRBUF_INIT;
 			child_process_init(cp);
-			cp->dir = task->repo->gitdir;
-			prepare_submodule_repo_env_in_gitdir(&cp->env_array);
+			cp->dir = task->repo->worktree;
+			prepare_submodule_repo_env(&cp->env_array);
 			cp->git_cmd = 1;
 			if (!spf->quiet)
 				strbuf_addf(err, _("Fetching submodule %s%s\n"),
@@ -1505,9 +1499,9 @@ static int get_next_submodule(struct child_process *cp,
 			    spf->prefix, task->sub->path);
 
 		child_process_init(cp);
-		prepare_submodule_repo_env_in_gitdir(&cp->env_array);
+		prepare_submodule_repo_env(&cp->env_array);
 		cp->git_cmd = 1;
-		cp->dir = task->repo->gitdir;
+		cp->dir = task->repo->worktree;
 
 		strvec_init(&cp->args);
 		strvec_pushv(&cp->args, spf->args.v);

t/t5526-fetch-submodules.sh

@@ -719,4 +719,67 @@ test_expect_success 'fetch new submodule commit intermittently referenced by sup
 	)
 '
 
+add_commit_push () {
+	dir="$1"
+	msg="$2"
+	shift 2
+	git -C "$dir" add "$@" &&
+	git -C "$dir" commit -a -m "$msg" &&
+	git -C "$dir" push
+}
+
+compare_refs_in_dir () {
+	fail= &&
+	if test "x$1" = 'x!'
+	then
+		fail='!' &&
+		shift
+	fi &&
+	git -C "$1" rev-parse --verify "$2" >expect &&
+	git -C "$3" rev-parse --verify "$4" >actual &&
+	eval $fail test_cmp expect actual
+}
+
+
+test_expect_success 'setup nested submodule fetch test' '
+	# does not depend on any previous test setups
+
+	for repo in outer middle inner
+	do
+		(
+			git init --bare $repo &&
+			git clone $repo ${repo}_content &&
+			echo "$repo" >"${repo}_content/file" &&
+			add_commit_push ${repo}_content "initial" file
+		) || return 1
+	done &&
+
+	git clone outer A &&
+	git -C A submodule add "$pwd/middle" &&
+	git -C A/middle/ submodule add "$pwd/inner" &&
+	add_commit_push A/middle/ "adding inner sub" .gitmodules inner &&
+	add_commit_push A/ "adding middle sub" .gitmodules middle &&
+
+	git clone outer B &&
+	git -C B/ submodule update --init middle &&
+
+	compare_refs_in_dir A HEAD B HEAD &&
+	compare_refs_in_dir A/middle HEAD B/middle HEAD &&
+	test -f B/file &&
+	test -f B/middle/file &&
+	! test -f B/middle/inner/file &&
+
+	echo "change on inner repo of A" >"A/middle/inner/file" &&
+	add_commit_push A/middle/inner "change on inner" file &&
+	add_commit_push A/middle "change on inner" inner &&
+	add_commit_push A "change on inner" middle
+'
+
+test_expect_success 'fetching a superproject containing an uninitialized sub/sub project' '
+	# depends on previous test for setup
+
+	git -C B/ fetch &&
+	compare_refs_in_dir A origin/master B origin/master
+'
+
 test_done