Made sure the Description and Validated retain optional; fixes #503 (#508)

Author: liuzicheng1987

src/rfl/json/to_schema.cpp

@@ -32,11 +32,18 @@ schema::Type type_to_json_schema_type(const parsing::schema::Type& _type,
                                       const bool _no_required);
 
 bool is_optional(const parsing::schema::Type& _t) {
-  const auto handle = [](const auto& _v) -> bool {
+  return _t.variant_.visit([&](const auto& _v) -> bool {
     using T = std::remove_cvref_t<decltype(_v)>;
-    return std::is_same<T, parsing::schema::Type::Optional>();
-  };
-  return rfl::visit(handle, _t.variant_);
+    if constexpr (std::is_same_v<T, parsing::schema::Type::Description>) {
+      return is_optional(*_v.type_);
+
+    } else if constexpr (std::is_same_v<T, parsing::schema::Type::Validated>) {
+      return is_optional(*_v.type_);
+
+    } else {
+      return std::is_same_v<T, parsing::schema::Type::Optional>;
+    }
+  });
 }
 
 std::string numeric_type_to_string(const parsing::schema::Type& _type) {

tests/json/test_json_schema5.cpp

@@ -0,0 +1,32 @@
+#include <iostream>
+#include <optional>
+#include <rfl.hpp>
+#include <rfl/json.hpp>
+#include <string>
+#include <tuple>
+#include <vector>
+
+#include "write_and_read.hpp"
+
+namespace test_json_schema5 {
+
+using Age = rfl::Validator<std::optional<unsigned int>, rfl::Minimum<0>,
+                           rfl::Maximum<130>>;
+
+struct Person {
+  rfl::Description<"Given name of this person", std::string> first_name;
+  rfl::Description<"Optional family name of this person",
+                   std::optional<std::string>>
+      last_name;
+  Age age;
+};
+
+TEST(json, test_json_schema5) {
+  const auto json_schema = rfl::json::to_schema<Person>();
+
+  const std::string expected =
+      R"({"$schema":"https://json-schema.org/draft/2020-12/schema","$ref":"#/definitions/test_json_schema5__Person","definitions":{"test_json_schema5__Person":{"type":"object","properties":{"first_name":{"type":"string","description":"Given name of this person"},"last_name":{"description":"Optional family name of this person","anyOf":[{"type":"string"},{"type":"null"}]},"age":{"allOf":[{"minimum":0,"type":"number"},{"maximum":130,"type":"number"}]}},"required":["first_name"]}}})";
+
+  EXPECT_EQ(json_schema, expected);
+}
+}  // namespace test_json_schema5