Add ObjectRef:get_children() (#10480)

Co-authored-by: Zughy <4279489-marco_a@users.noreply.gitlab.com>

doc/lua_api.txt

@@ -6206,6 +6206,8 @@ object you are working with still exists.
        should appear in first person.
 * `get_attach()`: returns parent, bone, position, rotation, forced_visible, 
     or nil if it isn't attached.
+* `get_children()`: returns a list of ObjectRefs that are attached to the
+    object.
 * `set_detach()`
 * `set_bone_position(bone, position, rotation)`
     * `bone`: string

src/script/lua_api/l_object.cpp

@@ -738,6 +738,27 @@ int ObjectRef::l_get_attach(lua_State *L)
 	return 5;
 }
 
+// get_children(self)
+int ObjectRef::l_get_children(lua_State *L)
+{
+	GET_ENV_PTR;
+
+	ObjectRef *ref = checkobject(L, 1);
+	ServerActiveObject *sao = getobject(ref);
+	if (sao == nullptr)
+		return 0;
+
+	const std::unordered_set<int> child_ids = sao->getAttachmentChildIds();
+	int i = 0;
+	lua_createtable(L, child_ids.size(), 0);
+	for (const int id : child_ids) {
+		ServerActiveObject *child = env->getActiveObject(id);
+		getScriptApiBase(L)->objectrefGetOrCreate(L, child);
+		lua_rawseti(L, -2, ++i);
+	}
+	return 1;
+}
+
 // set_detach(self)
 int ObjectRef::l_set_detach(lua_State *L)
 {
@@ -2337,6 +2358,7 @@ luaL_Reg ObjectRef::methods[] = {
 	luamethod(ObjectRef, get_bone_position),
 	luamethod(ObjectRef, set_attach),
 	luamethod(ObjectRef, get_attach),
+	luamethod(ObjectRef, get_children),
 	luamethod(ObjectRef, set_detach),
 	luamethod(ObjectRef, set_properties),
 	luamethod(ObjectRef, get_properties),

src/script/lua_api/l_object.h

@@ -143,6 +143,9 @@ private:
 	// get_attach(self)
 	static int l_get_attach(lua_State *L);
 
+	// get_children(self)
+	static int l_get_children(lua_State *L);
+
 	// set_detach(self)
 	static int l_set_detach(lua_State *L);