[MP] Convert _spawn_custom to a Callable property.

Renamed to "spawn_function".
Allow both custom spawn and auto spawn list to co-exist.

This makes it possible to implement custom spawn without being forced to
attach a script to MultiplayerSpawner directly.

modules/multiplayer/doc_classes/MultiplayerSpawner.xml

@@ -5,20 +5,12 @@
 	</brief_description>
 	<description>
 		Spawnable scenes can be configured in the editor or through code (see [method add_spawnable_scene]).
-		Also supports custom node spawns through [method spawn], calling [method _spawn_custom] on all peers.
+		Also supports custom node spawns through [method spawn], calling [member spawn_function] on all peers.
 		Internally, [MultiplayerSpawner] uses [method MultiplayerAPI.object_configuration_add] to notify spawns passing the spawned node as the [code]object[/code] and itself as the [code]configuration[/code], and [method MultiplayerAPI.object_configuration_remove] to notify despawns in a similar way.
 	</description>
 	<tutorials>
 	</tutorials>
 	<methods>
-		<method name="_spawn_custom" qualifiers="virtual">
-			<return type="Node" />
-			<param index="0" name="data" type="Variant" />
-			<description>
-				Method called on all peers when a custom spawn was requested by the authority using [method spawn]. Should return a [Node] that is not in the scene tree.
-				[b]Note:[/b] Spawned nodes should [b]not[/b] be added to the scene with [method Node.add_child]. This is done automatically.
-			</description>
-		</method>
 		<method name="add_spawnable_scene">
 			<return type="void" />
 			<param index="0" name="path" type="String" />
@@ -49,12 +41,16 @@
 			<return type="Node" />
 			<param index="0" name="data" type="Variant" default="null" />
 			<description>
-				Requests a custom spawn, with [code]data[/code] passed to [method _spawn_custom] on all peers. Returns the locally spawned node instance already inside the scene tree, and added as a child of the node pointed by [member spawn_path].
+				Requests a custom spawn, with [code]data[/code] passed to [member spawn_function] on all peers. Returns the locally spawned node instance already inside the scene tree, and added as a child of the node pointed by [member spawn_path].
 				[b]Note:[/b] Spawnable scenes are spawned automatically. [method spawn] is only needed for custom spawns.
 			</description>
 		</method>
 	</methods>
 	<members>
+		<member name="spawn_function" type="Callable" setter="set_spawn_function" getter="get_spawn_function">
+			Method called on all peers when for every custom [method spawn] requested by the authority. Will receive the [code]data[/code] parameter, and should return a [Node] that is not in the scene tree.
+			[b]Note:[/b] The returned node should [b]not[/b] be added to the scene with [method Node.add_child]. This is done automatically.
+		</member>
 		<member name="spawn_limit" type="int" setter="set_spawn_limit" getter="get_spawn_limit" default="0">
 			Maximum nodes that is allowed to be spawned by this spawner. Includes both spawnable scenes and custom spawns.
 			When set to [code]0[/code] (the default), there is no limit.

modules/multiplayer/multiplayer_spawner.cpp

@@ -93,13 +93,6 @@ PackedStringArray MultiplayerSpawner::get_configuration_warnings() const {
 	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;
 }
 
@@ -162,7 +155,9 @@ void MultiplayerSpawner::_bind_methods() {
 	ClassDB::bind_method(D_METHOD("set_spawn_limit", "limit"), &MultiplayerSpawner::set_spawn_limit);
 	ADD_PROPERTY(PropertyInfo(Variant::INT, "spawn_limit", PROPERTY_HINT_RANGE, "0,1024,1,or_greater"), "set_spawn_limit", "get_spawn_limit");
 
-	GDVIRTUAL_BIND(_spawn_custom, "data");
+	ClassDB::bind_method(D_METHOD("get_spawn_function"), &MultiplayerSpawner::get_spawn_function);
+	ClassDB::bind_method(D_METHOD("set_spawn_function", "spawn_function"), &MultiplayerSpawner::set_spawn_function);
+	ADD_PROPERTY(PropertyInfo(Variant::CALLABLE, "spawn_function", PROPERTY_HINT_NONE, "", PROPERTY_USAGE_NO_EDITOR), "set_spawn_function", "get_spawn_function");
 
 	ADD_SIGNAL(MethodInfo("despawned", PropertyInfo(Variant::OBJECT, "node", PROPERTY_HINT_RESOURCE_TYPE, "Node")));
 	ADD_SIGNAL(MethodInfo("spawned", PropertyInfo(Variant::OBJECT, "node", PROPERTY_HINT_RESOURCE_TYPE, "Node")));
@@ -183,7 +178,7 @@ void MultiplayerSpawner::_update_spawn_node() {
 	Node *node = spawn_path.is_empty() && is_inside_tree() ? nullptr : get_node_or_null(spawn_path);
 	if (node) {
 		spawn_node = node->get_instance_id();
-		if (get_spawnable_scene_count() && !GDVIRTUAL_IS_OVERRIDDEN(_spawn_custom)) {
+		if (get_spawnable_scene_count()) {
 			node->connect("child_entered_tree", callable_mp(this, &MultiplayerSpawner::_node_added));
 		}
 	} else {
@@ -298,23 +293,26 @@ Node *MultiplayerSpawner::instantiate_scene(int p_id) {
 
 Node *MultiplayerSpawner::instantiate_custom(const Variant &p_data) {
 	ERR_FAIL_COND_V_MSG(spawn_limit && spawn_limit <= tracked_nodes.size(), nullptr, "Spawn limit reached!");
-	Node *node = nullptr;
-	if (GDVIRTUAL_CALL(_spawn_custom, p_data, node)) {
-		return node;
-	}
-	ERR_FAIL_V_MSG(nullptr, "Method '_spawn_custom' is not implemented on this peer.");
+	ERR_FAIL_COND_V_MSG(!spawn_function.is_valid(), nullptr, "Custom spawn requires a valid 'spawn_function'.");
+	const Variant *argv[1] = { &p_data };
+	Variant ret;
+	Callable::CallError ce;
+	spawn_function.callp(argv, 1, ret, ce);
+	ERR_FAIL_COND_V_MSG(ce.error != Callable::CallError::CALL_OK, nullptr, "Failed to call spawn function.");
+	ERR_FAIL_COND_V_MSG(ret.get_type() != Variant::OBJECT, nullptr, "The spawn function must return a Node.");
+	return Object::cast_to<Node>(ret.operator Object *());
 }
 
 Node *MultiplayerSpawner::spawn(const Variant &p_data) {
 	ERR_FAIL_COND_V(!is_inside_tree() || !get_multiplayer()->has_multiplayer_peer() || !is_multiplayer_authority(), nullptr);
 	ERR_FAIL_COND_V_MSG(spawn_limit && spawn_limit <= tracked_nodes.size(), nullptr, "Spawn limit reached!");
-	ERR_FAIL_COND_V_MSG(!GDVIRTUAL_IS_OVERRIDDEN(_spawn_custom), nullptr, "Custom spawn requires the '_spawn_custom' virtual method to be implemented via script.");
+	ERR_FAIL_COND_V_MSG(!spawn_function.is_valid(), nullptr, "Custom spawn requires the 'spawn_function' property to be a valid callable.");
 
 	Node *parent = get_spawn_node();
 	ERR_FAIL_COND_V_MSG(!parent, nullptr, "Cannot find spawn node.");
 
 	Node *node = instantiate_custom(p_data);
-	ERR_FAIL_COND_V_MSG(!node, nullptr, "The '_spawn_custom' implementation must return a valid Node.");
+	ERR_FAIL_COND_V_MSG(!node, nullptr, "The 'spawn_function' callable must return a valid node.");
 
 	_track(node, p_data);
 	parent->add_child(node, true);

modules/multiplayer/multiplayer_spawner.h

@@ -71,6 +71,7 @@ private:
 	ObjectID spawn_node;
 	HashMap<ObjectID, SpawnInfo> tracked_nodes;
 	uint32_t spawn_limit = 0;
+	Callable spawn_function;
 
 	void _update_spawn_node();
 	void _track(Node *p_node, const Variant &p_argument, int p_scene_id = INVALID_ID);
@@ -106,6 +107,8 @@ public:
 	void set_spawn_path(const NodePath &p_path);
 	uint32_t get_spawn_limit() const { return spawn_limit; }
 	void set_spawn_limit(uint32_t p_limit) { spawn_limit = p_limit; }
+	void set_spawn_function(Callable p_spawn_function) { spawn_function = p_spawn_function; }
+	Callable get_spawn_function() const { return spawn_function; }
 
 	const Variant get_spawn_argument(const ObjectID &p_id) const;
 	int find_spawnable_scene_index_from_object(const ObjectID &p_id) const;
@@ -114,8 +117,6 @@ public:
 	Node *instantiate_custom(const Variant &p_data);
 	Node *instantiate_scene(int p_idx);
 
-	GDVIRTUAL1R(Node *, _spawn_custom, const Variant &);
-
 	MultiplayerSpawner() {}
 };