Merge branch 'develop' into claude/deep-copy-key-comp-5649

Conflicts:
- tests/src/unit-comparison.cpp: kept both sides' helpers (key_case_less/
  key_case_json/innermost from the PR, case_insensitive_less/ci_json from
  develop's #5720) and both new test cases

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

docs/docset/docSet.sql

@@ -16,7 +16,6 @@ INSERT INTO searchIndex(name, type, path) VALUES ('basic_json', 'Class', 'api/ba
 INSERT INTO searchIndex(name, type, path) VALUES ('basic_json::accept', 'Function', 'api/basic_json/accept/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('basic_json::array', 'Function', 'api/basic_json/array/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('basic_json::array_t', 'Type', 'api/basic_json/array_t/index.html');
-INSERT INTO searchIndex(name, type, path) VALUES ('basic_json::as_base_class', 'Method', 'api/basic_json/as_base_class/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('basic_json::at', 'Method', 'api/basic_json/at/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('basic_json::back', 'Method', 'api/basic_json/back/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('basic_json::basic_json', 'Constructor', 'api/basic_json/basic_json/index.html');

docs/mkdocs/docs/api/basic_json/as_base_class.md

@@ -1,53 +0,0 @@
-# <small>nlohmann::basic_json::</small>as_base_class
-
-```cpp
-json_base_class_t& as_base_class() noexcept;
-const json_base_class_t& as_base_class() const noexcept;
-```
-
-Returns a reference to this object as its custom base class [`json_base_class_t`](json_base_class_t.md). No copy is
-made.
-
-Since `basic_json` derives from `json_base_class_t`, a member of `basic_json` hides any member of the custom base class
-with the same name. This function makes such hidden members accessible again.
-
-## Return value
-
-reference to this object as [`json_base_class_t`](json_base_class_t.md)
-
-## Exception safety
-
-No-throw guarantee: this function never throws exceptions.
-
-## Complexity
-
-Constant.
-
-## Notes
-
-The function is equivalent to `static_cast<json_base_class_t&>(j)` (or `static_cast<const json_base_class_t&>(j)`).
-
-## Examples
-
-??? example
-
-    The example shows how to use `as_base_class` to access members of the custom base class that are hidden by members
-    of `basic_json`.
-    
-    ```cpp
-    --8<-- "examples/as_base_class.cpp"
-    ```
-    
-    Output:
-    
-    ```json
-    --8<-- "examples/as_base_class.output"
-    ```
-
-## See also
-
-- [json_base_class_t](json_base_class_t.md) - type of the custom base class
-
-## Version history
-
-- Added in version 3.13.0.

docs/mkdocs/docs/api/basic_json/index.md

@@ -200,7 +200,6 @@ Direct access to the stored value of a JSON value.
 - [**get_ref**](get_ref.md) - get a reference value
 - [**operator ValueType**](operator_ValueType.md) - get a value
 - [**get_binary**](get_binary.md) - get a binary value
-- [**as_base_class**](as_base_class.md) - access the custom base class
 
 ### Element access
 

docs/mkdocs/docs/api/basic_json/json_base_class_t.md

@@ -27,18 +27,6 @@ A `CustomBaseClass` with non-static data members forfeits `basic_json`'s
 [standard layout](https://en.cppreference.com/w/cpp/named_req/StandardLayoutType) guarantee. See
 [Template Parameter Requirements](../../features/types/template_parameters.md#custombaseclass).
 
-#### Name conflicts
-
-Since `basic_json` derives from `CustomBaseClass`, members of `basic_json` hide members of `CustomBaseClass` with the
-same name. Hidden members remain accessible via [`as_base_class`](as_base_class.md) or by casting the value to
-`json_base_class_t`.
-
-!!! warning "Avoid generic member names"
-
-    Future versions of the library may add members to `basic_json` that hide members of `CustomBaseClass` that are
-    accessible today. To reduce the risk of such conflicts, avoid generic names for the members of `CustomBaseClass`,
-    for instance by using a distinctive prefix.
-
 ## Examples
 
 ??? example
@@ -55,11 +43,6 @@ same name. Hidden members remain accessible via [`as_base_class`](as_base_class.
     --8<-- "examples/json_base_class_t.output"
     ```
 
-## See also
-
-- [as_base_class](as_base_class.md) - access the custom base class
-
 ## Version history
 
 - Added in version 3.12.0.
-- Made a public member type in version 3.13.0; it was private before, so it could not be named outside the class.

docs/mkdocs/docs/examples/as_base_class.cpp

@@ -1,41 +0,0 @@
-#include <iostream>
-#include <nlohmann/json.hpp>
-
-class base_class_with_hidden_members
-{
-  public:
-    const char* type_name() const noexcept
-    {
-        return "my_type_name";
-    }
-
-    std::size_t size() const noexcept
-    {
-        return 42;
-    }
-};
-
-using json = nlohmann::basic_json <
-             std::map,
-             std::vector,
-             std::string,
-             bool,
-             std::int64_t,
-             std::uint64_t,
-             double,
-             std::allocator,
-             nlohmann::adl_serializer,
-             std::vector<std::uint8_t>,
-             base_class_with_hidden_members
-             >;
-
-int main()
-{
-    json j = {1, 2, 3};
-
-    // the members of basic_json hide the members of the base class
-    std::cout << j.type_name() << ' ' << j.size() << '\n';
-
-    // access the hidden members of the base class
-    std::cout << j.as_base_class().type_name() << ' ' << j.as_base_class().size() << '\n';
-}

docs/mkdocs/docs/examples/as_base_class.output

@@ -1,2 +0,0 @@
-array 3
-my_type_name 42

docs/mkdocs/mkdocs.yml

@@ -114,7 +114,6 @@ nav:
           - 'accept': api/basic_json/accept.md
           - 'array': api/basic_json/array.md
           - 'array_t': api/basic_json/array_t.md
-          - 'as_base_class': api/basic_json/as_base_class.md
           - 'at': api/basic_json/at.md
           - 'back': api/basic_json/back.md
           - 'begin': api/basic_json/begin.md

include/nlohmann/detail/meta/type_traits.hpp

@@ -189,6 +189,37 @@ struct actual_object_comparator
 template<typename BasicJsonType>
 using actual_object_comparator_t = typename actual_object_comparator<BasicJsonType>::type;
 
+template<typename T>
+using detect_key_comp = decltype(std::declval<const T&>().key_comp());
+
+// whether ObjectType can be constructed from a pair of Iterator together with
+// a copy of its own comparator, the way std::map can: it needs a nested
+// key_compare, a const key_comp() convertible to it, and a matching
+// (Iterator, Iterator, const key_compare&) constructor.
+//
+// used to preserve a stateful comparator when a copy is built from a range
+// past the iterative deep copy's nesting bound (see copy_object_level); an
+// object type that does not satisfy this, such as nlohmann::ordered_map
+// (which has key_compare for its std::map-like interface, but no key_comp()),
+// keeps default-constructing its comparator, just as it always has
+template<typename ObjectType, typename Iterator, typename = void>
+struct is_comparator_constructible_object_type_impl : std::false_type {};
+
+template<typename ObjectType, typename Iterator>
+struct is_comparator_constructible_object_type_impl <
+    ObjectType, Iterator, enable_if_t<is_detected<detect_key_compare, ObjectType>::value >>
+{
+    using key_compare = typename ObjectType::key_compare;
+
+    static constexpr bool value =
+        is_detected_convertible<key_compare, detect_key_comp, ObjectType>::value &&
+        std::is_constructible<ObjectType, Iterator, Iterator, const key_compare&>::value;
+};
+
+template<typename ObjectType, typename Iterator>
+struct is_comparator_constructible_object_type
+    : is_comparator_constructible_object_type_impl<ObjectType, Iterator> {};
+
 /////////////////
 // char_traits //
 /////////////////

include/nlohmann/json.hpp

@@ -155,6 +155,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
 
     /// workaround type for MSVC
     using basic_json_t = NLOHMANN_BASIC_JSON_TPL;
+    using json_base_class_t = ::nlohmann::detail::json_base_class<CustomBaseClass>;
 
   JSON_PRIVATE_UNLESS_TESTED:
     // convenience aliases for types residing in namespace detail;
@@ -214,9 +215,6 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     using cbor_tag_handler_t = detail::cbor_tag_handler_t;
     /// how to encode BJData
     using bjdata_version_t = detail::bjdata_version_t;
-    /// base class used to inject custom functionality into each instance of basic_json
-    /// @sa https://json.nlohmann.me/api/basic_json/json_base_class_t/
-    using json_base_class_t = ::nlohmann::detail::json_base_class<CustomBaseClass>;
     /// helper type for initializer lists of basic_json values
     using initializer_list_t = std::initializer_list<detail::json_ref<basic_json>>;
 
@@ -1129,6 +1127,27 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         }
     }
 
+    /// @brief create the object type from a range, preserving @a src_object's
+    /// comparator when the object type supports it
+    /// Enabled for object types that provide a key_comp() and a matching
+    /// range-plus-comparator constructor, such as std::map. Other object
+    /// types, such as nlohmann::ordered_map, fall back to the plain range
+    /// constructor and default-construct their comparator, just as they
+    /// always have (@ref detail::is_comparator_constructible_object_type).
+    template<typename Iterator, detail::enable_if_t<
+                 detail::is_comparator_constructible_object_type<object_t, Iterator>::value, int> = 0>
+    static object_t* create_object_with_comparator(const object_t& src_object, Iterator first, Iterator last)
+    {
+        return create<object_t>(first, last, src_object.key_comp());
+    }
+
+    template<typename Iterator, detail::enable_if_t<
+                 detail::negation<detail::is_comparator_constructible_object_type<object_t, Iterator>>::value, int> = 0>
+    static object_t* create_object_with_comparator(const object_t& /*src_object*/, Iterator first, Iterator last)
+    {
+        return create<object_t>(first, last);
+    }
+
     /// @brief create the copy of the object @a src in @a dst
     /// @note structured values are appended to @a worklist instead
     static void copy_object_level(const basic_json& src, basic_json& dst,
@@ -1146,7 +1165,8 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
             scratch.emplace_back(element.first, basic_json());
         }
 
-        dst.m_data.m_value.object = create<object_t>(std::make_move_iterator(scratch.begin()),
+        dst.m_data.m_value.object = create_object_with_comparator(src_object,
+                                    std::make_move_iterator(scratch.begin()),
                                     std::make_move_iterator(scratch.end()));
         // only now that the object exists may dst stop being a null value
         dst.m_data.m_type = value_t::object;
@@ -2693,20 +2713,6 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         return *get_ptr<const binary_t*>();
     }
 
-    /// @brief access the custom base class
-    /// @sa https://json.nlohmann.me/api/basic_json/as_base_class/
-    json_base_class_t& as_base_class() noexcept
-    {
-        return static_cast<json_base_class_t&>(*this);
-    }
-
-    /// @brief access the custom base class
-    /// @sa https://json.nlohmann.me/api/basic_json/as_base_class/
-    const json_base_class_t& as_base_class() const noexcept
-    {
-        return static_cast<const json_base_class_t&>(*this);
-    }
-
     /// @}
 
     ////////////////////

single_include/nlohmann/json.hpp

@@ -4197,6 +4197,37 @@ struct actual_object_comparator
 template<typename BasicJsonType>
 using actual_object_comparator_t = typename actual_object_comparator<BasicJsonType>::type;
 
+template<typename T>
+using detect_key_comp = decltype(std::declval<const T&>().key_comp());
+
+// whether ObjectType can be constructed from a pair of Iterator together with
+// a copy of its own comparator, the way std::map can: it needs a nested
+// key_compare, a const key_comp() convertible to it, and a matching
+// (Iterator, Iterator, const key_compare&) constructor.
+//
+// used to preserve a stateful comparator when a copy is built from a range
+// past the iterative deep copy's nesting bound (see copy_object_level); an
+// object type that does not satisfy this, such as nlohmann::ordered_map
+// (which has key_compare for its std::map-like interface, but no key_comp()),
+// keeps default-constructing its comparator, just as it always has
+template<typename ObjectType, typename Iterator, typename = void>
+struct is_comparator_constructible_object_type_impl : std::false_type {};
+
+template<typename ObjectType, typename Iterator>
+struct is_comparator_constructible_object_type_impl <
+    ObjectType, Iterator, enable_if_t<is_detected<detect_key_compare, ObjectType>::value >>
+{
+    using key_compare = typename ObjectType::key_compare;
+
+    static constexpr bool value =
+        is_detected_convertible<key_compare, detect_key_comp, ObjectType>::value &&
+        std::is_constructible<ObjectType, Iterator, Iterator, const key_compare&>::value;
+};
+
+template<typename ObjectType, typename Iterator>
+struct is_comparator_constructible_object_type
+    : is_comparator_constructible_object_type_impl<ObjectType, Iterator> {};
+
 /////////////////
 // char_traits //
 /////////////////
@@ -27082,6 +27113,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
 
     /// workaround type for MSVC
     using basic_json_t = NLOHMANN_BASIC_JSON_TPL;
+    using json_base_class_t = ::nlohmann::detail::json_base_class<CustomBaseClass>;
 
   JSON_PRIVATE_UNLESS_TESTED:
     // convenience aliases for types residing in namespace detail;
@@ -27141,9 +27173,6 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     using cbor_tag_handler_t = detail::cbor_tag_handler_t;
     /// how to encode BJData
     using bjdata_version_t = detail::bjdata_version_t;
-    /// base class used to inject custom functionality into each instance of basic_json
-    /// @sa https://json.nlohmann.me/api/basic_json/json_base_class_t/
-    using json_base_class_t = ::nlohmann::detail::json_base_class<CustomBaseClass>;
     /// helper type for initializer lists of basic_json values
     using initializer_list_t = std::initializer_list<detail::json_ref<basic_json>>;
 
@@ -28056,6 +28085,27 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         }
     }
 
+    /// @brief create the object type from a range, preserving @a src_object's
+    /// comparator when the object type supports it
+    /// Enabled for object types that provide a key_comp() and a matching
+    /// range-plus-comparator constructor, such as std::map. Other object
+    /// types, such as nlohmann::ordered_map, fall back to the plain range
+    /// constructor and default-construct their comparator, just as they
+    /// always have (@ref detail::is_comparator_constructible_object_type).
+    template<typename Iterator, detail::enable_if_t<
+                 detail::is_comparator_constructible_object_type<object_t, Iterator>::value, int> = 0>
+    static object_t* create_object_with_comparator(const object_t& src_object, Iterator first, Iterator last)
+    {
+        return create<object_t>(first, last, src_object.key_comp());
+    }
+
+    template<typename Iterator, detail::enable_if_t<
+                 detail::negation<detail::is_comparator_constructible_object_type<object_t, Iterator>>::value, int> = 0>
+    static object_t* create_object_with_comparator(const object_t& /*src_object*/, Iterator first, Iterator last)
+    {
+        return create<object_t>(first, last);
+    }
+
     /// @brief create the copy of the object @a src in @a dst
     /// @note structured values are appended to @a worklist instead
     static void copy_object_level(const basic_json& src, basic_json& dst,
@@ -28073,7 +28123,8 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
             scratch.emplace_back(element.first, basic_json());
         }
 
-        dst.m_data.m_value.object = create<object_t>(std::make_move_iterator(scratch.begin()),
+        dst.m_data.m_value.object = create_object_with_comparator(src_object,
+                                    std::make_move_iterator(scratch.begin()),
                                     std::make_move_iterator(scratch.end()));
         // only now that the object exists may dst stop being a null value
         dst.m_data.m_type = value_t::object;
@@ -29620,20 +29671,6 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         return *get_ptr<const binary_t*>();
     }
 
-    /// @brief access the custom base class
-    /// @sa https://json.nlohmann.me/api/basic_json/as_base_class/
-    json_base_class_t& as_base_class() noexcept
-    {
-        return static_cast<json_base_class_t&>(*this);
-    }
-
-    /// @brief access the custom base class
-    /// @sa https://json.nlohmann.me/api/basic_json/as_base_class/
-    const json_base_class_t& as_base_class() const noexcept
-    {
-        return static_cast<const json_base_class_t&>(*this);
-    }
-
     /// @}
 
     ////////////////////

tests/src/unit-comparison.cpp

@@ -827,6 +827,46 @@ Json nest(Json j, const std::size_t depth)
     return j;
 }
 
+// a std::map comparator with state: case-insensitive, unless constructed
+// case-sensitive. Used to check that copying an object copies the original's
+// comparator rather than default-constructing a new one (see #5649).
+struct key_case_less
+{
+    key_case_less() = default;
+    explicit key_case_less(const bool cs) noexcept : case_sensitive(cs) {}
+
+    bool operator()(const std::string& a, const std::string& b) const
+    {
+        if (case_sensitive)
+        {
+            return a < b;
+        }
+        return std::lexicographical_compare(a.begin(), a.end(), b.begin(), b.end(),
+                                            [](unsigned char x, unsigned char y)
+        {
+            return std::tolower(x) < std::tolower(y);
+        });
+    }
+
+    bool case_sensitive = false;
+};
+
+template<class Key, class Value, class /*Compare*/, class Allocator>
+using key_case_map = std::map<Key, Value, key_case_less, Allocator>;
+using key_case_json = nlohmann::basic_json<key_case_map>;
+
+// the innermost value of a chain of single-element arrays
+template<typename Json>
+const Json& innermost(const Json& j)
+{
+    const Json* p = &j;
+    while (p->is_array())
+    {
+        p = &(*p)[0];
+    }
+    return *p;
+}
+
 // orders keys case-insensitively, so "key" and "KEY" compare equivalent
 // (neither less than the other) although they are not equal
 struct case_insensitive_less
@@ -891,6 +931,47 @@ TEST_CASE("equality of objects whose entries have no fixed order")
     }
 }
 
+TEST_CASE("copying an object preserves its comparator's state")
+{
+    // Past the iterative deep copy's nesting bound, an object copy used to be
+    // built with a default-constructed comparator instead of a copy of the
+    // original's. For an object type whose comparator carries state - here, a
+    // std::map that compares keys case-sensitively only when created that way
+    // - this reordered the copy's keys and could even drop entries that the
+    // original's comparator kept distinct (see #5649).
+    key_case_json object = key_case_json::object_t(key_case_less(true)); // case-sensitive
+    object["b"] = 1;
+    object["B"] = 2;
+    object["a"] = 3;
+    REQUIRE(object.dump() == R"({"B":2,"a":3,"b":1})");
+
+    for (const std::size_t depth : std::vector<std::size_t> {0, 127, 128, 200})
+    {
+        CAPTURE(depth);
+
+        key_case_json original = object;
+        for (std::size_t i = 0; i < depth; ++i)
+        {
+            original = key_case_json::array({std::move(original)});
+        }
+
+        {
+            const key_case_json copy = original; // NOLINT(performance-unnecessary-copy-initialization)
+            CHECK(innermost(copy).size() == 3);
+            CHECK(innermost(copy).dump() == R"({"B":2,"a":3,"b":1})");
+            CHECK(copy == original);
+        }
+
+        {
+            key_case_json copy = key_case_json::array();
+            copy = original;
+            CHECK(innermost(copy).size() == 3);
+            CHECK(innermost(copy).dump() == R"({"B":2,"a":3,"b":1})");
+            CHECK(copy == original);
+        }
+    }
+}
+
 TEST_CASE("equality of an object whose comparator treats different keys as equivalent")
 {
     // https://github.com/nlohmann/json/issues/5655: past the nesting bound,

tests/src/unit-custom-base-class.cpp

@@ -10,8 +10,6 @@
 #include <set>
 #include <sstream>
 #include <string>
-#include <type_traits>
-#include <utility>
 #include <vector>
 
 #include "doctest_compatibility.h"
@@ -407,71 +405,3 @@ TEST_CASE("JSON Visit Node")
         );
     CHECK(expected.empty());
 }
-
-// Test accessing members of a custom base class that are hidden by members of nlohmann::basic_json
-class base_class_with_hidden_members
-{
-  public:
-    const char* type_name() const noexcept // NOLINT(readability-convert-member-functions-to-static)
-    {
-        return "custom type_name";
-    }
-
-    std::size_t size() const noexcept
-    {
-        return m_size;
-    }
-
-    std::size_t m_size = 42;
-};
-
-using json_with_hidden_base_members =
-    nlohmann::basic_json <
-    std::map,
-    std::vector,
-    std::string,
-    bool,
-    std::int64_t,
-    std::uint64_t,
-    double,
-    std::allocator,
-    nlohmann::adl_serializer,
-    std::vector<std::uint8_t>,
-    base_class_with_hidden_members
-    >;
-
-TEST_CASE("JSON Node as_base_class")
-{
-    using json = json_with_hidden_base_members;
-
-    static_assert(std::is_same<decltype(std::declval<json&>().as_base_class()), json::json_base_class_t&>::value, "");
-    static_assert(std::is_same<decltype(std::declval<const json&>().as_base_class()), const json::json_base_class_t&>::value, "");
-    static_assert(noexcept(std::declval<json&>().as_base_class()), "");
-    static_assert(noexcept(std::declval<const json&>().as_base_class()), "");
-
-    SECTION("non-const")
-    {
-        json j = {1, 2, 3};
-
-        CHECK(std::string(j.type_name()) == "array");
-        CHECK(j.size() == 3);
-        CHECK(std::string(j.as_base_class().type_name()) == "custom type_name");
-        CHECK(j.as_base_class().size() == 42);
-        CHECK(&j.as_base_class() == &static_cast<json::json_base_class_t&>(j));
-
-        j.as_base_class().m_size = 7;
-        CHECK(j.as_base_class().size() == 7);
-        CHECK(j.size() == 3);
-    }
-
-    SECTION("const")
-    {
-        const json j = {1, 2, 3};
-
-        CHECK(std::string(j.type_name()) == "array");
-        CHECK(j.size() == 3);
-        CHECK(std::string(j.as_base_class().type_name()) == "custom type_name");
-        CHECK(j.as_base_class().size() == 42);
-        CHECK(&j.as_base_class() == &static_cast<const json::json_base_class_t&>(j));
-    }
-}