diff --git a/include/nlohmann/json.hpp b/include/nlohmann/json.hpp index d18baf599..abd461d6c 100644 --- a/include/nlohmann/json.hpp +++ b/include/nlohmann/json.hpp @@ -1492,13 +1492,28 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec compare_keys(current.lhs_object_it->first, current.rhs_object_it->first, std::integral_constant {}); - if (key_result != compare_result::equal) - { - return key_result; - } - left = &(current.lhs_object_it->second); right = &(current.rhs_object_it->second); + + if (key_result != compare_result::equal) + { + // An object type without a fixed order of its entries - + // std::unordered_map, say - may enumerate two equal + // objects differently, and its operator== does not care. + // Equality then finds the entry by its key; an ordering, + // or an object type that compares its entries in + // sequence (ordered_map), is decided by the key itself. + const auto* rhs_object = current.rhs_value->m_data.m_value.object; + const auto found = (!Ordered && !detail::is_ordered_map::value) + ? rhs_object->find(current.lhs_object_it->first) + : rhs_object->cend(); + if (found == rhs_object->cend()) + { + return key_result; + } + right = &(found->second); + } + ++current.lhs_object_it; ++current.rhs_object_it; } diff --git a/single_include/nlohmann/json.hpp b/single_include/nlohmann/json.hpp index b5938be0e..ba41273de 100644 --- a/single_include/nlohmann/json.hpp +++ b/single_include/nlohmann/json.hpp @@ -26361,13 +26361,28 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec compare_keys(current.lhs_object_it->first, current.rhs_object_it->first, std::integral_constant {}); - if (key_result != compare_result::equal) - { - return key_result; - } - left = &(current.lhs_object_it->second); right = &(current.rhs_object_it->second); + + if (key_result != compare_result::equal) + { + // An object type without a fixed order of its entries - + // std::unordered_map, say - may enumerate two equal + // objects differently, and its operator== does not care. + // Equality then finds the entry by its key; an ordering, + // or an object type that compares its entries in + // sequence (ordered_map), is decided by the key itself. + const auto* rhs_object = current.rhs_value->m_data.m_value.object; + const auto found = (!Ordered && !detail::is_ordered_map::value) + ? rhs_object->find(current.lhs_object_it->first) + : rhs_object->cend(); + if (found == rhs_object->cend()) + { + return key_result; + } + right = &(found->second); + } + ++current.lhs_object_it; ++current.rhs_object_it; } diff --git a/tests/src/unit-comparison.cpp b/tests/src/unit-comparison.cpp index 9a6606256..69c0103c9 100644 --- a/tests/src/unit-comparison.cpp +++ b/tests/src/unit-comparison.cpp @@ -15,7 +15,13 @@ #include "doctest_compatibility.h" +#include + #include +#include +#include +#include +#include #define JSON_TESTS_PRIVATE #include @@ -745,6 +751,127 @@ TEST_CASE("regression #3868 - heterogeneous comparisons compile under C++20 (P24 } #endif +namespace +{ +// orders keys ascending or descending, as chosen when a map is created +template +class directed_less +{ + public: + directed_less() = default; + + explicit directed_less(const bool descending) noexcept + : m_descending(descending) + {} + + bool operator()(const Key& lhs, const Key& rhs) const + { + return m_descending ? rhs < lhs : lhs < rhs; + } + + private: + bool m_descending = false; +}; + +// An object type that, like std::unordered_map, enumerates its entries in no +// fixed order - ascending or descending by key, depending on how the map was +// created - and whose operator== does not depend on that order. +// std::unordered_map itself cannot be used here: the standard does not +// require it to accept an incomplete mapped type such as basic_json, and +// libstdc++ 6 to 9 as well as the EDG front ends of icpc and nvc++ reject +// basic_json. std::map, the default object type, works +// with all supported compilers. +template +struct unordered_object_t : std::map, Allocator> +{ + using base_type = std::map, Allocator>; + using base_type::base_type; + + friend bool operator==(const unordered_object_t& lhs, const unordered_object_t& rhs) + { + return lhs.size() == rhs.size() && std::all_of(lhs.begin(), lhs.end(), [&rhs](const std::pair& entry) + { + const auto it = rhs.find(entry.first); + return it != rhs.end() && it->second == entry.second; + }); + } + + friend bool operator!=(const unordered_object_t& lhs, const unordered_object_t& rhs) + { + return !(lhs == rhs); + } +}; +using unordered_json = nlohmann::basic_json; + +// the entries "0" to "9", enumerated in ascending or in descending order +unordered_json make_unordered_object(const bool descending) +{ + unordered_json j = unordered_json::object_t(directed_less(descending)); + for (int i = 0; i < 10; ++i) + { + j[std::to_string(i)] = i; + } + return j; +} + +template +Json nest(Json j, const std::size_t depth) +{ + for (std::size_t i = 0; i < depth; ++i) + { + Json outer = Json::object(); + outer["x"] = std::move(j); + j = std::move(outer); + } + return j; +} +} // namespace + +TEST_CASE("equality of objects whose entries have no fixed order") +{ + // Values nested deeper than a bound are compared without the call stack, + // entry by entry. That must agree with the object type's own operator==, + // which for unordered_object_t (as for std::unordered_map) does not + // depend on the order of the entries, and for ordered_map does. + REQUIRE(make_unordered_object(true).begin().key() == "9"); + REQUIRE(make_unordered_object(false).begin().key() == "0"); + + for (const std::size_t depth : std::vector {0, 200}) + { + CAPTURE(depth); + + const unordered_json descending = nest(make_unordered_object(true), depth); + const unordered_json ascending = nest(make_unordered_object(false), depth); + CHECK(descending == ascending); + CHECK_FALSE(descending != ascending); + + // a copy is equal to its original + const unordered_json copy = descending; // NOLINT(performance-unnecessary-copy-initialization) + CHECK(copy == descending); + + // a different value, a different key, or another entry still count + unordered_json other_value = make_unordered_object(true); + other_value["5"] = 42; + CHECK_FALSE(nest(other_value, depth) == ascending); + + unordered_json other_key = make_unordered_object(true); + other_key.erase("5"); + other_key["50"] = 5; + CHECK_FALSE(nest(other_key, depth) == ascending); + + unordered_json more_entries = make_unordered_object(true); + more_entries["10"] = 10; + CHECK_FALSE(nest(more_entries, depth) == ascending); + CHECK_FALSE(ascending == nest(more_entries, depth)); + + // ordered_json compares its entries in sequence + const nlohmann::ordered_json ab = nest(nlohmann::ordered_json({{"a", 1}, {"b", 2}}), depth); + const nlohmann::ordered_json ba = nest(nlohmann::ordered_json({{"b", 2}, {"a", 1}}), depth); + CHECK_FALSE(ab == ba); + CHECK(ab != ba); + } +} + TEST_CASE("containers are compared element by element") { // Containers nested deeper than a bound are compared without the call