fix: Prevent reassignment of base value when retrieving None.

Author: heinezen

nyan/nyan_tool.cpp

@@ -27,17 +27,17 @@ int test_parser(const std::string &base_path, const std::string &filename) {
 
 	std::shared_ptr<View> root = db->new_view();
 
+	Object test = root->get_object("test.Test");
 	Object second = root->get_object("test.Second");
 	Object first = root->get_object("test.First");
 
 	std::cout << "before change: First.member == "
 	          << *root->get_object("test.First").get<Int>("member")
 	          << std::endl;
 
-	std::optional<std::shared_ptr<Object>> optional_wat3 = first.get_optional<Object>("wat3", 0);
-
-	if (optional_wat3.has_value()) {
-		if ((*optional_wat3)->get_name() != "test.Second") {
+	std::optional<std::shared_ptr<Object>> wat3_first = first.get_optional<Object>("wat3", 0);
+	if (wat3_first.has_value()) {
+		if ((*wat3_first)->get_name() != "test.Second") {
 			std::cout << "First.wat3 has wrong value at t=0" << std::endl;
 			return 1;
 		}
@@ -47,6 +47,19 @@ int test_parser(const std::string &base_path, const std::string &filename) {
 		return 1;
 	}
 
+	std::optional<std::shared_ptr<Object>> wat3_second = second.get_optional<Object, true>("wat3", 0);
+	if (wat3_second.has_value()) {
+		std::cout << "Second.wat3 should be None" << std::endl;
+		return 1;
+	}
+
+	std::optional<std::shared_ptr<Object>> wat3_test = test.get_optional<Object, true>("wat3", 0);
+	if (wat3_test.has_value()) {
+		std::cout << "Test.wat3 should be None" << std::endl;
+		return 1;
+	}
+
+
 	Object patch = root->get_object("test.FirstPatch");
 	for (int i = 0; i < 3; i++) {
 		Transaction tx = root->new_transaction();
@@ -56,8 +69,8 @@ int test_parser(const std::string &base_path, const std::string &filename) {
 		}
 	}
 
-	optional_wat3 = first.get_optional<Object>("wat3");
-	if (optional_wat3.has_value()) {
+	wat3_first = first.get_optional<Object>("wat3");
+	if (wat3_first.has_value()) {
 		std::cout << "First.wat3 should be None by patch" << std::endl;
 		return 1;
 	}
@@ -250,7 +263,6 @@ std::pair<flags_t, params_t> argparse(int argc, char** argv) {
 
 
 int main(int argc, char **argv) {
-
 	auto args = nyan::argparse(argc, argv);
 	nyan::flags_t flags = args.first;
 	nyan::params_t params = args.second;

nyan/object.cpp

@@ -1,4 +1,4 @@
-// Copyright 2016-2023 the nyan authors, LGPLv3+. See copying.md for legal info.
+// Copyright 2016-2024 the nyan authors, LGPLv3+. See copying.md for legal info.
 
 #include "object.h"
 
@@ -170,15 +170,16 @@ ValueHolder Object::calculate_value(const memberid_t &member, order_t t) const {
 	ValueHolder result = base_value->copy();
 
 	// walk back and apply the value changes
-	while (true) {
-		const Member *change = parents[defined_by]->get(member);
+
+	// skip the parent that assigns the value
+	// this prevents reassignment errors e.g. from assigning None
+	int parent_idx = defined_by - 1;
+	while (parent_idx >= 0) {
+		const Member *change = parents[parent_idx]->get(member);
 		if (change != nullptr) {
 			result->apply(*change);
 		}
-		if (defined_by == 0) {
-			break;
-		}
-		defined_by -= 1;
+		parent_idx -= 1;
 	}
 
 	return result;

test/test.nyan

@@ -28,6 +28,7 @@ Second(First):
     member *= 5.5
     First.nice_member = False
     # nap : int
+    wat3 = None
 
 NestingBase(First):