Merge branch 'jt/submodule-pull-recurse-rebase'

"git pull -recurse-submodules --rebase", when the submodule
repository's history did not have anything common between ours and
the upstream's, failed to execute.  We need to fetch from them to
continue even in such a case.

* jt/submodule-pull-recurse-rebase:
  submodule: do not pass null OID to setup_revisions

submodule.c

@@ -1169,8 +1169,10 @@ int submodule_touches_in_range(struct object_id *excl_oid,
 
 	argv_array_push(&args, "--"); /* args[0] program name */
 	argv_array_push(&args, oid_to_hex(incl_oid));
-	argv_array_push(&args, "--not");
-	argv_array_push(&args, oid_to_hex(excl_oid));
+	if (!is_null_oid(excl_oid)) {
+		argv_array_push(&args, "--not");
+		argv_array_push(&args, oid_to_hex(excl_oid));
+	}
 
 	collect_changed_submodules(&subs, &args);
 	ret = subs.nr;

submodule.h

@@ -92,7 +92,10 @@ extern int bad_to_remove_submodule(const char *path, unsigned flags);
 
 int add_submodule_odb(const char *path);
 
-/* Checks if there are submodule changes in a..b. */
+/*
+ * Checks if there are submodule changes in a..b. If a is the null OID,
+ * checks b and all its ancestors instead.
+ */
 extern int submodule_touches_in_range(struct object_id *a,
 				      struct object_id *b);
 extern int find_unpushed_submodules(struct oid_array *commits,

t/t5572-pull-submodule.sh

@@ -132,4 +132,25 @@ test_expect_success 'pull rebase recursing fails with conflicts' '
 	test_i18ngrep "locally recorded submodule modifications" err
 '
 
+test_expect_success 'branch has no merge base with remote-tracking counterpart' '
+	rm -rf parent child &&
+
+	test_create_repo a-submodule &&
+	test_commit -C a-submodule foo &&
+
+	test_create_repo parent &&
+	git -C parent submodule add "$(pwd)/a-submodule" &&
+	git -C parent commit -m foo &&
+
+	git clone parent child &&
+
+	# Reset master so that it has no merge base with
+	# refs/remotes/origin/master.
+	OTHER=$(git -C child commit-tree -m bar \
+		$(git -C child rev-parse HEAD^{tree})) &&
+	git -C child reset --hard "$OTHER" &&
+
+	git -C child pull --recurse-submodules --rebase
+'
+
 test_done