forked from lix-project/lix
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 commit02bd821f2e
) Change-Id:I8b0ebcf2af4226610dadd565962f2d2327415a03
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parent
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@ -78,20 +78,29 @@ namespace nlohmann {
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*/
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template<typename T>
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struct adl_serializer<std::optional<T>> {
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static std::optional<T> from_json(const json & json) {
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/**
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* @brief Convert a JSON type to an `optional<T>` treating
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* `null` as `std::nullopt`.
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*/
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static void from_json(const json & json, std::optional<T> & t) {
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static_assert(
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nix::json_avoids_null<T>::value,
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"null is already in use for underlying type's JSON");
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return json.is_null()
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t = json.is_null()
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? std::nullopt
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: std::optional { adl_serializer<T>::from_json(json) };
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: std::make_optional(json.template get<T>());
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}
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static void to_json(json & json, std::optional<T> t) {
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/**
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* @brief Convert an optional type to a JSON type treating `std::nullopt`
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* as `null`.
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*/
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static void to_json(json & json, const std::optional<T> & t) {
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static_assert(
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nix::json_avoids_null<T>::value,
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"null is already in use for underlying type's JSON");
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if (t)
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adl_serializer<T>::to_json(json, *t);
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json = *t;
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else
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json = nullptr;
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}
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58
tests/unit/libutil/json-utils.cc
Normal file
58
tests/unit/libutil/json-utils.cc
Normal file
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@ -0,0 +1,58 @@
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#include <vector>
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#include <optional>
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#include <gtest/gtest.h>
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#include "json-utils.hh"
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namespace nix {
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/* Test `to_json` and `from_json` with `std::optional` types.
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* We are specifically interested in whether we can _nest_ optionals in STL
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* containers so we that we can leverage existing adl_serializer templates. */
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TEST(to_json, optionalInt) {
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std::optional<int> val = std::make_optional(420);
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ASSERT_EQ(nlohmann::json(val), nlohmann::json(420));
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val = std::nullopt;
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ASSERT_EQ(nlohmann::json(val), nlohmann::json(nullptr));
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}
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TEST(to_json, vectorOfOptionalInts) {
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std::vector<std::optional<int>> vals = {
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std::make_optional(420),
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std::nullopt,
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};
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ASSERT_EQ(nlohmann::json(vals), nlohmann::json::parse("[420,null]"));
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}
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TEST(to_json, optionalVectorOfInts) {
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std::optional<std::vector<int>> val = std::make_optional(std::vector<int> {
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-420,
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420,
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});
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ASSERT_EQ(nlohmann::json(val), nlohmann::json::parse("[-420,420]"));
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val = std::nullopt;
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ASSERT_EQ(nlohmann::json(val), nlohmann::json(nullptr));
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}
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TEST(from_json, optionalInt) {
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nlohmann::json json = 420;
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std::optional<int> val = json;
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ASSERT_TRUE(val.has_value());
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ASSERT_EQ(*val, 420);
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json = nullptr;
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json.get_to(val);
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ASSERT_FALSE(val.has_value());
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}
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TEST(from_json, vectorOfOptionalInts) {
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nlohmann::json json = { 420, nullptr };
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std::vector<std::optional<int>> vals = json;
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ASSERT_EQ(vals.size(), 2);
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ASSERT_TRUE(vals.at(0).has_value());
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ASSERT_EQ(*vals.at(0), 420);
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ASSERT_FALSE(vals.at(1).has_value());
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}
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} /* namespace nix */
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