7 files changed, 41 insertions, 4 deletions
diff --git a/modules/multiplayer/SCsub b/modules/multiplayer/SCsub
index ff33655537..e89038c3e0 100644
--- a/modules/multiplayer/SCsub
+++ b/modules/multiplayer/SCsub
@@ -8,7 +8,7 @@ env_mp = env_modules.Clone()
 module_obj = []
 env_mp.add_source_files(module_obj, "*.cpp")
 
-if env["tools"]:
+if env.editor_build:
     env_mp.add_source_files(module_obj, "editor/*.cpp")
 
 env.modules_sources += module_obj
diff --git a/modules/multiplayer/doc_classes/MultiplayerSynchronizer.xml b/modules/multiplayer/doc_classes/MultiplayerSynchronizer.xml
index 9a4d755d64..42c190f504 100644
--- a/modules/multiplayer/doc_classes/MultiplayerSynchronizer.xml
+++ b/modules/multiplayer/doc_classes/MultiplayerSynchronizer.xml
@@ -5,7 +5,7 @@
 	</brief_description>
 	<description>
 		By default, [MultiplayerSynchronizer] synchronizes configured properties to all peers.
-		Visiblity can be handled directly with [method set_visibility_for] or as-needed with [method add_visibility_filter] and [method update_visibility].
+		Visibility can be handled directly with [method set_visibility_for] or as-needed with [method add_visibility_filter] and [method update_visibility].
 
 		[MultiplayerSpawner]s will handle nodes according to visibility of synchronizers as long as the node at [member root_path] was spawned by one.
 
@@ -34,7 +34,7 @@
 			<return type="void" />
 			<param index="0" name="filter" type="Callable" />
 			<description>
-				Removes a peer visiblity filter from this synchronizer.
+				Removes a peer visibility filter from this synchronizer.
 			</description>
 		</method>
 		<method name="set_visibility_for">
diff --git a/modules/multiplayer/multiplayer_spawner.cpp b/modules/multiplayer/multiplayer_spawner.cpp
index d46972ffb6..620e4f2f6c 100644
--- a/modules/multiplayer/multiplayer_spawner.cpp
+++ b/modules/multiplayer/multiplayer_spawner.cpp
@@ -86,6 +86,23 @@ void MultiplayerSpawner::_get_property_list(List<PropertyInfo> *p_list) const {
 	}
 }
 #endif
+
+PackedStringArray MultiplayerSpawner::get_configuration_warnings() const {
+	PackedStringArray warnings = Node::get_configuration_warnings();
+
+	if (spawn_path.is_empty() || !has_node(spawn_path)) {
+		warnings.push_back(RTR("A valid NodePath must be set in the \"Spawn Path\" property in order for MultiplayerSpawner to be able to spawn Nodes."));
+	}
+	bool has_scenes = get_spawnable_scene_count() > 0;
+	// Can't check if method is overridden in placeholder scripts.
+	bool has_placeholder_script = get_script_instance() && get_script_instance()->is_placeholder();
+	if (!has_scenes && !GDVIRTUAL_IS_OVERRIDDEN(_spawn_custom) && !has_placeholder_script) {
+		warnings.push_back(RTR("A list of PackedScenes must be set in the \"Auto Spawn List\" property in order for MultiplayerSpawner to automatically spawn them remotely when added as child of \"spawn_path\"."));
+		warnings.push_back(RTR("Alternatively, a Script implementing the function \"_spawn_custom\" must be set for this MultiplayerSpawner, and \"spawn\" must be called explicitly in code."));
+	}
+	return warnings;
+}
+
 void MultiplayerSpawner::add_spawnable_scene(const String &p_path) {
 	SpawnableScene sc;
 	sc.path = p_path;
@@ -94,13 +111,16 @@ void MultiplayerSpawner::add_spawnable_scene(const String &p_path) {
 	}
 	spawnable_scenes.push_back(sc);
 }
+
 int MultiplayerSpawner::get_spawnable_scene_count() const {
 	return spawnable_scenes.size();
 }
+
 String MultiplayerSpawner::get_spawnable_scene(int p_idx) const {
 	ERR_FAIL_INDEX_V(p_idx, (int)spawnable_scenes.size(), "");
 	return spawnable_scenes[p_idx].path;
 }
+
 void MultiplayerSpawner::clear_spawnable_scenes() {
 	spawnable_scenes.clear();
 }
diff --git a/modules/multiplayer/multiplayer_spawner.h b/modules/multiplayer/multiplayer_spawner.h
index fc3befc2d4..587c99efd1 100644
--- a/modules/multiplayer/multiplayer_spawner.h
+++ b/modules/multiplayer/multiplayer_spawner.h
@@ -91,6 +91,8 @@ protected:
 	void _get_property_list(List<PropertyInfo> *p_list) const;
 #endif
 public:
+	PackedStringArray get_configuration_warnings() const override;
+
 	Node *get_spawn_node() const {
 		return spawn_node.is_valid() ? Object::cast_to<Node>(ObjectDB::get_instance(spawn_node)) : nullptr;
 	}
diff --git a/modules/multiplayer/multiplayer_synchronizer.cpp b/modules/multiplayer/multiplayer_synchronizer.cpp
index eee1495c14..2c3ebccaeb 100644
--- a/modules/multiplayer/multiplayer_synchronizer.cpp
+++ b/modules/multiplayer/multiplayer_synchronizer.cpp
@@ -94,6 +94,16 @@ void MultiplayerSynchronizer::_update_process() {
 	}
 }
 
+PackedStringArray MultiplayerSynchronizer::get_configuration_warnings() const {
+	PackedStringArray warnings = Node::get_configuration_warnings();
+
+	if (root_path.is_empty() || !has_node(root_path)) {
+		warnings.push_back(RTR("A valid NodePath must be set in the \"Root Path\" property in order for MultiplayerSynchronizer to be able to synchronize properties."));
+	}
+
+	return warnings;
+}
+
 Error MultiplayerSynchronizer::get_state(const List<NodePath> &p_properties, Object *p_obj, Vector<Variant> &r_variant, Vector<const Variant *> &r_variant_ptrs) {
 	ERR_FAIL_COND_V(!p_obj, ERR_INVALID_PARAMETER);
 	r_variant.resize(p_properties.size());
diff --git a/modules/multiplayer/multiplayer_synchronizer.h b/modules/multiplayer/multiplayer_synchronizer.h
index e84d41db86..f10a95a1d4 100644
--- a/modules/multiplayer/multiplayer_synchronizer.h
+++ b/modules/multiplayer/multiplayer_synchronizer.h
@@ -66,6 +66,8 @@ public:
 	static Error get_state(const List<NodePath> &p_properties, Object *p_obj, Vector<Variant> &r_variant, Vector<const Variant *> &r_variant_ptrs);
 	static Error set_state(const List<NodePath> &p_properties, Object *p_obj, const Vector<Variant> &p_state);
 
+	PackedStringArray get_configuration_warnings() const override;
+
 	void set_replication_interval(double p_interval);
 	double get_replication_interval() const;
 	uint64_t get_replication_interval_msec() const;
diff --git a/modules/multiplayer/scene_replication_interface.cpp b/modules/multiplayer/scene_replication_interface.cpp
index 6e3dbfab47..53d8e82dfc 100644
--- a/modules/multiplayer/scene_replication_interface.cpp
+++ b/modules/multiplayer/scene_replication_interface.cpp
@@ -125,9 +125,12 @@ Error SceneReplicationInterface::on_replication_start(Object *p_obj, Variant p_c
 	MultiplayerSynchronizer *sync = Object::cast_to<MultiplayerSynchronizer>(p_config.get_validated_object());
 	ERR_FAIL_COND_V(!sync, ERR_INVALID_PARAMETER);
 
+	const ObjectID oid = node->get_instance_id();
+	MultiplayerSpawner *spawner = rep_state->get_spawner(oid);
+	ERR_FAIL_COND_V_MSG(spawner && spawner->get_multiplayer_authority() != sync->get_multiplayer_authority(), ERR_INVALID_PARAMETER, "The authority of the MultiplayerSynchronizer \"" + String(sync->get_path()) + "\" differs from the authority of its \"root_node\" spawner and will not sync. Change the \"root_node\" of the MultiplayerSynchronizer to be a child of the scene root instead.");
+
 	// Add to synchronizer list and setup visibility.
 	rep_state->config_add_sync(node, sync);
-	const ObjectID oid = node->get_instance_id();
 	sync->connect("visibility_changed", callable_mp(this, &SceneReplicationInterface::_visibility_changed).bind(oid));
 	if (multiplayer->has_multiplayer_peer() && sync->is_multiplayer_authority()) {
 		_update_sync_visibility(0, oid);