fix: nlohmann::adl_serializer for std::optional (#9147)

This allows templates such as `NLOHMANN_DEFINE_TYPE_*` templates and other generators with things like `std::vector<std::optional<T>>`.

Co-authored-by: John Ericson <John.Ericson@Obsidian.Systems>
(cherry picked from commit 02bd821f2e)
Change-Id: I8b0ebcf2af4226610dadd565962f2d2327415a03
This commit is contained in:
eldritch horrors 2024-03-04 06:08:39 +01:00
parent b7c61d337b
commit c208e918e5
2 changed files with 72 additions and 5 deletions

View file

@ -78,20 +78,29 @@ namespace nlohmann {
*/
template<typename T>
struct adl_serializer<std::optional<T>> {
static std::optional<T> from_json(const json & json) {
/**
* @brief Convert a JSON type to an `optional<T>` treating
* `null` as `std::nullopt`.
*/
static void from_json(const json & json, std::optional<T> & t) {
static_assert(
nix::json_avoids_null<T>::value,
"null is already in use for underlying type's JSON");
return json.is_null()
t = json.is_null()
? std::nullopt
: std::optional { adl_serializer<T>::from_json(json) };
: std::make_optional(json.template get<T>());
}
static void to_json(json & json, std::optional<T> t) {
/**
* @brief Convert an optional type to a JSON type treating `std::nullopt`
* as `null`.
*/
static void to_json(json & json, const std::optional<T> & t) {
static_assert(
nix::json_avoids_null<T>::value,
"null is already in use for underlying type's JSON");
if (t)
adl_serializer<T>::to_json(json, *t);
json = *t;
else
json = nullptr;
}

View file

@ -0,0 +1,58 @@
#include <vector>
#include <optional>
#include <gtest/gtest.h>
#include "json-utils.hh"
namespace nix {
/* Test `to_json` and `from_json` with `std::optional` types.
* We are specifically interested in whether we can _nest_ optionals in STL
* containers so we that we can leverage existing adl_serializer templates. */
TEST(to_json, optionalInt) {
std::optional<int> val = std::make_optional(420);
ASSERT_EQ(nlohmann::json(val), nlohmann::json(420));
val = std::nullopt;
ASSERT_EQ(nlohmann::json(val), nlohmann::json(nullptr));
}
TEST(to_json, vectorOfOptionalInts) {
std::vector<std::optional<int>> vals = {
std::make_optional(420),
std::nullopt,
};
ASSERT_EQ(nlohmann::json(vals), nlohmann::json::parse("[420,null]"));
}
TEST(to_json, optionalVectorOfInts) {
std::optional<std::vector<int>> val = std::make_optional(std::vector<int> {
-420,
420,
});
ASSERT_EQ(nlohmann::json(val), nlohmann::json::parse("[-420,420]"));
val = std::nullopt;
ASSERT_EQ(nlohmann::json(val), nlohmann::json(nullptr));
}
TEST(from_json, optionalInt) {
nlohmann::json json = 420;
std::optional<int> val = json;
ASSERT_TRUE(val.has_value());
ASSERT_EQ(*val, 420);
json = nullptr;
json.get_to(val);
ASSERT_FALSE(val.has_value());
}
TEST(from_json, vectorOfOptionalInts) {
nlohmann::json json = { 420, nullptr };
std::vector<std::optional<int>> vals = json;
ASSERT_EQ(vals.size(), 2);
ASSERT_TRUE(vals.at(0).has_value());
ASSERT_EQ(*vals.at(0), 420);
ASSERT_FALSE(vals.at(1).has_value());
}
} /* namespace nix */