test-bus-vtable: also print introspection for the fallback vtable

This doesn't really test anything, it's just a trivial test that we
get the expected output for a fallback vtable.

src/libsystemd/sd-bus/test-bus-vtable.c

@@ -19,9 +19,24 @@
 
 #define DEFAULT_BUS_PATH "unix:path=/run/dbus/system_bus_socket"
 
+static struct context c = {};
+static int happy_finder_object = 0;
+
+static int happy_finder(sd_bus *bus, const char *path, const char *interface, void *userdata, void **found, sd_bus_error *error) {
+        assert(userdata);
+        assert(userdata == &c);
+
+#ifndef __cplusplus
+        log_info("%s called", __func__);
+#endif
+
+        happy_finder_object++;
+        *found = &happy_finder_object;
+        return 1; /* found */
+}
+
 static void test_vtable(void) {
         sd_bus *bus = NULL;
-        struct context c = {};
         int r;
 
         assert(sd_bus_new(&bus) >= 0);
@@ -32,16 +47,23 @@ static void test_vtable(void) {
         assert(sd_bus_add_object_vtable(bus, NULL, "/foo", "org.freedesktop.systemd.testVtable221",
                                         (const sd_bus_vtable *)vtable_format_221, &c) >= 0);
 
+        assert(sd_bus_add_fallback_vtable(bus, NULL, "/fallback", "org.freedesktop.systemd.testVtable2", test_vtable_2, happy_finder, &c) >= 0);
+
         assert(sd_bus_set_address(bus, DEFAULT_BUS_PATH) >= 0);
         r = sd_bus_start(bus);
         assert(r == 0 ||     /* success */
                r == -ENOENT  /* dbus is inactive */ );
 
 #ifndef __cplusplus
-        _cleanup_free_ char *s = NULL;
+        _cleanup_free_ char *s, *s2;
 
         assert_se(introspect_path(bus, "/foo", NULL, false, true, NULL, &s, NULL) == 1);
         fputs(s, stdout);
+
+        assert_se(introspect_path(bus, "/fallback", NULL, false, true, NULL, &s2, NULL) == 1);
+        fputs(s2, stdout);
+
+        assert_se(happy_finder_object == 1);
 #endif
 
         sd_bus_unref(bus);

src/libsystemd/sd-bus/test-vtable-data.h

@@ -42,7 +42,7 @@ static const sd_bus_vtable test_vtable_1[] = {
 
 static const sd_bus_vtable test_vtable_2[] = {
         SD_BUS_VTABLE_START(0),
-        SD_BUS_METHOD("AlterSomething", "s", "s", handler, 0),
+        SD_BUS_METHOD("AlterSomething", "s", "s", handler, SD_BUS_VTABLE_UNPRIVILEGED),
         SD_BUS_METHOD("Exit", "", "", handler, 0),
         SD_BUS_METHOD_WITH_OFFSET("AlterSomething2", "s", "s", handler, 200, 0),
         SD_BUS_METHOD_WITH_OFFSET("Exit2", "", "", handler, 200, 0),