Add persistent unique identifiers for objects (#14135)

src/script/cpp_api/s_base.cpp

@@ -406,17 +406,13 @@ void ScriptApiBase::setOriginFromTableRaw(int index, const char *fxn)
 /*
  * How ObjectRefs are handled in Lua:
  * When an active object is created, an ObjectRef is created on the Lua side
- * and stored in core.object_refs[id].
+ * and stored in core.object_refs[id] and in core.objects_by_guids[GUID].
  * Methods that require an ObjectRef to a certain object retrieve it from that
- * table instead of creating their own.(*)
+ * table instead of creating their own.
  * When an active object is removed, the existing ObjectRef is invalidated
- * using ::set_null() and removed from the core.object_refs table.
- * (*) An exception to this are NULL ObjectRefs and anonymous ObjectRefs
- *     for objects without ID.
- *     It's unclear what the latter are needed for and their use is problematic
- *     since we lose control over the ref and the contained pointer.
+ * using ::set_null() and removed from the core.object_refs and
+ * core.object_by_guids tables.
  */
-
 void ScriptApiBase::addObjectReference(ServerActiveObject *cobj)
 {
 	SCRIPTAPI_PRECHECKHEADER
@@ -434,8 +430,20 @@ void ScriptApiBase::addObjectReference(ServerActiveObject *cobj)
 
 	// object_refs[id] = object
 	lua_pushinteger(L, cobj->getId()); // Push id
-	lua_pushvalue(L, object); // Copy object to top of stack
+	lua_pushvalue(L, object);
 	lua_settable(L, objectstable);
+
+	// Get core.objects_by_guid table
+	lua_getglobal(L, "core");
+	lua_getfield(L, -1, "objects_by_guid");
+	luaL_checktype(L, -1, LUA_TTABLE);
+	objectstable = lua_gettop(L);
+
+	// objects_by_guid[guid] = object
+	auto guid = cobj->getGUID();
+	assert(!guid.empty());
+	lua_pushvalue(L, object);
+	lua_setfield(L, objectstable, guid.c_str());
 }
 
 void ScriptApiBase::removeObjectReference(ServerActiveObject *cobj)
@@ -445,6 +453,8 @@ void ScriptApiBase::removeObjectReference(ServerActiveObject *cobj)
 
 	// Get core.object_refs table
 	lua_getglobal(L, "core");
+	int core = lua_gettop(L);
+
 	lua_getfield(L, -1, "object_refs");
 	luaL_checktype(L, -1, LUA_TTABLE);
 	int objectstable = lua_gettop(L);
@@ -460,6 +470,15 @@ void ScriptApiBase::removeObjectReference(ServerActiveObject *cobj)
 	lua_pushinteger(L, cobj->getId()); // Push id
 	lua_pushnil(L);
 	lua_settable(L, objectstable);
+
+	// Get core.objects_by_guid
+	lua_getfield(L, core, "objects_by_guid");
+	luaL_checktype(L, -1, LUA_TTABLE);
+	objectstable = lua_gettop(L);
+
+	// Set objects_by_guid[guid] = nil
+	lua_pushnil(L);
+	lua_setfield(L, objectstable, cobj->getGUID().c_str());
 }
 
 void ScriptApiBase::objectrefGetOrCreate(lua_State *L, ServerActiveObject *cobj)

src/script/lua_api/l_object.cpp

@@ -119,6 +119,20 @@ int ObjectRef::l_is_valid(lua_State *L)
 	return 1;
 }
 
+// get_guid()
+int ObjectRef::l_get_guid(lua_State *L)
+{
+	NO_MAP_LOCK_REQUIRED;
+	ObjectRef *ref = checkObject<ObjectRef>(L, 1);
+	ServerActiveObject *sao = getobject(ref);
+	if (sao == nullptr)
+		return 0;
+
+	std::string guid = sao->getGUID();
+	lua_pushlstring(L, guid.c_str(), guid.size());
+	return 1;
+}
+
 // get_pos(self)
 int ObjectRef::l_get_pos(lua_State *L)
 {
@@ -2838,6 +2852,7 @@ luaL_Reg ObjectRef::methods[] = {
 	// ServerActiveObject
 	luamethod(ObjectRef, remove),
 	luamethod(ObjectRef, is_valid),
+	luamethod(ObjectRef, get_guid),
 	luamethod_aliased(ObjectRef, get_pos, getpos),
 	luamethod_aliased(ObjectRef, set_pos, setpos),
 	luamethod(ObjectRef, add_pos),

src/script/lua_api/l_object.h

@@ -61,6 +61,9 @@ private:
 	// is_valid(self)
 	static int l_is_valid(lua_State *L);
 
+	// get_guid()
+	static int l_get_guid(lua_State *L);
+
 	// get_pos(self)
 	static int l_get_pos(lua_State *L);
 

src/script/scripting_server.cpp

@@ -62,6 +62,9 @@ ServerScripting::ServerScripting(Server* server):
 	lua_newtable(L);
 	lua_setfield(L, -2, "object_refs");
 
+	lua_newtable(L);
+	lua_setfield(L, -2, "objects_by_guid");
+
 	lua_newtable(L);
 	lua_setfield(L, -2, "luaentities");