Make sure that flag enum with value zero are correctly serialized; fixes #640

Author: liuzicheng1987

include/rfl/enums.hpp

@@ -1,14 +1,14 @@
 #ifndef RFL_ENUMS_HPP_
 #define RFL_ENUMS_HPP_
 
-#include <string>
 #include <sstream>
+#include <string>
 
 #include "Result.hpp"
 #include "internal/enums/get_enum_names.hpp"
 #include "internal/strings/strings.hpp"
-#include "thirdparty/enchantum/enchantum.hpp"
 #include "thirdparty/enchantum/bitflags.hpp"
+#include "thirdparty/enchantum/enchantum.hpp"
 
 namespace rfl {
 
@@ -77,6 +77,9 @@ std::string enum_to_string(const EnumType _enum) {
       ++i;
       val >>= 1;
     }
+    if (flags.empty()) {
+      return "0";
+    }
     return internal::strings::join("|", flags);
   } else {
     return to_string_or_number(_enum);

tests/json/test_enum8.cpp

@@ -0,0 +1,36 @@
+#include <gtest/gtest.h>
+
+#include <cassert>
+#include <rfl.hpp>
+#include <rfl/json.hpp>
+
+#include "write_and_read.hpp"
+
+namespace test_enum8 {
+
+enum class TestEnum : uint64_t {
+  None = 0,
+  Hello = 1 << 0,
+  World = 1 << 1,
+  HelloWorld = Hello | World
+};
+
+TestEnum operator|(TestEnum a, TestEnum b) noexcept {
+  return static_cast<TestEnum>(static_cast<uint64_t>(a) |
+                               static_cast<uint64_t>(b));
+}
+
+struct SomeClass {
+  TestEnum e;
+  TestEnum f;
+  TestEnum g;
+};
+
+TEST(json, test_enum8) {
+  SomeClass t{
+      .e = TestEnum::None, .f = TestEnum::Hello, .g = TestEnum::HelloWorld};
+
+  write_and_read(t, R"({"e":"0","f":"Hello","g":"Hello|World"})");
+}
+
+}  // namespace test_enum8