Merge branch 'develop' into claude/ordered-json-emplace-lvalue-5673

Conflicts:
- include/nlohmann/ordered_map.hpp: both emplace() overloads call
  develop's new append() helper (#5609) with the PR's std::forward<V>(t)
- single_include/nlohmann/json.hpp: regenerated with make amalgamate

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

docs/mkdocs/docs/api/basic_json/emplace.md

@@ -69,3 +69,5 @@ Logarithmic in the size of the container, O(log(`size()`)).
 ## Version history
 
 - Since version 2.0.8.
+- Fixed in version 3.13.0: for [`ordered_json`](../ordered_json.md), the value could previously only be passed as an
+  rvalue; it can now also be passed as an lvalue or a `#!cpp const` lvalue, matching the behavior of `json`.

include/nlohmann/json.hpp

@@ -1004,38 +1004,18 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     using copy_scratch_value_t = std::pair<typename object_t::key_type, basic_json>;
     using copy_scratch_t = std::vector<copy_scratch_value_t, AllocatorType<copy_scratch_value_t>>;
 
-    /// @brief tag selecting the constructor below; used only to build the
-    /// elements of a deep copy (@ref copy_array_level, @ref copy_object_level)
-    struct copy_construct_tag {};
-
-  public:
-    /*!
-    @brief construct a null value whose base class - and, with @ref
-           JSON_DIAGNOSTIC_POSITIONS, positions - are copied from @a src
-
-    Copy-constructing @ref json_base_class_t here, rather than default-
-    constructing the element and assigning its base class afterwards, means
-    that copying a @ref basic_json only ever requires a copy-constructible
-    base class, and never a move-assignable one as well.
-
-    @note this constructor has to be public: @ref copy_array_level and
-          @ref copy_object_level reach it through @ref array_t's or @ref
-          object_t's own emplace_back(), which constructs the element from
-          outside @ref basic_json and so cannot call a private constructor.
-          @ref copy_construct_tag is private, though, and nothing in the
-          public interface hands out a value of it, so outside code can still
-          never name it to call this constructor itself.
-    */
-    basic_json(copy_construct_tag /*unused*/, const basic_json& src)
-        : json_base_class_t(src)
-#if JSON_DIAGNOSTIC_POSITIONS
-        , start_position(src.start_position)
-        , end_position(src.end_position)
-#endif
+    /// @brief copy everything of @a src into @a dst but its type and value
+    static void copy_metadata(const basic_json& src, basic_json& dst)
     {
-    }
+        // a custom base class is only required to be copy-constructible and
+        // move-assignable, so the copy has to go through a temporary
+        static_cast<json_base_class_t&>(dst) = json_base_class_t(static_cast<const json_base_class_t&>(src));
 
-  private:
+#if JSON_DIAGNOSTIC_POSITIONS
+        dst.start_position = src.start_position;
+        dst.end_position = src.end_position;
+#endif
+    }
 
     /*!
     @brief copy the value of @a src into @a dst, which must not be structured
@@ -1099,11 +1079,8 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     }
 
     /*!
-    @brief finish the copy @a dst of @a src that a @ref copy_construct_tag
-           constructor started, other than the children of an object or array
+    @brief copy everything of @a src into the null value @a dst but the children
 
-    @a dst already has @a src's base class and, with @ref
-    JSON_DIAGNOSTIC_POSITIONS, positions; only its value is still missing.
     Objects and arrays are not copied here; they are appended to @a worklist to
     be created later by @ref copy_iteratively. Until that happens, @a dst remains
     a null value, so that a partially built copy can be destroyed at any point
@@ -1111,6 +1088,8 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     */
     static void copy_shallow(const basic_json& src, basic_json& dst, copy_worklist_t& worklist)
     {
+        copy_metadata(src, dst);
+
         if (src.m_data.m_type == value_t::object || src.m_data.m_type == value_t::array)
         {
             // defer: dst stays a null value until its container exists
@@ -1131,19 +1110,15 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     {
         const array_t& src_array = *src.m_data.m_value.array;
 
+        // create all elements up front: growing the array afterwards could
+        // invalidate the pointers that are handed to the worklist; resize()
+        // rather than the fill constructor, because not every array type
+        // provides the latter (e.g., ones without a matching allocator-aware
+        // fill constructor)
         dst.m_data.m_value.array = create<array_t>();
         // only now that the array exists may dst stop being a null value
         dst.m_data.m_type = value_t::array;
-
-        // create every element - its base class already copy-constructed from
-        // its counterpart in src, via the copy_construct_tag constructor -
-        // before any of their addresses are handed to worklist below: growing
-        // the array while that is going on could reallocate it and invalidate
-        // addresses taken from an earlier iteration
-        for (const auto& src_element : src_array)
-        {
-            dst.m_data.m_value.array->emplace_back(copy_construct_tag{}, src_element);
-        }
+        dst.m_data.m_value.array->resize(src_array.size());
 
         auto dst_it = dst.m_data.m_value.array->begin();
         for (auto src_it = src_array.cbegin(); src_it != src_array.cend(); ++src_it, ++dst_it)
@@ -1161,14 +1136,12 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
 
         // build the complete key skeleton and hand it to the object's range
         // constructor: adding the keys one by one would be quadratic for object
-        // types that are backed by a vector, such as nlohmann::ordered_map; each
-        // value's base class is already copy-constructed from its counterpart
-        // in src, via the copy_construct_tag constructor
+        // types that are backed by a vector, such as nlohmann::ordered_map
         scratch.clear();
         scratch.reserve(src_object.size());
         for (const auto& element : src_object)
         {
-            scratch.emplace_back(element.first, basic_json(copy_construct_tag{}, element.second));
+            scratch.emplace_back(element.first, basic_json());
         }
 
         dst.m_data.m_value.object = create<object_t>(std::make_move_iterator(scratch.begin()),

include/nlohmann/ordered_map.hpp

@@ -72,7 +72,9 @@ template <class Key, class T, class IgnoredLess = std::less<Key>,
         return *this;
     }
 
-    std::pair<iterator, bool> emplace(const key_type& key, T&& t)
+    template<class V, detail::enable_if_t<
+                 detail::is_constructible<T, V>::value, int> = 0>
+    std::pair<iterator, bool> emplace(const key_type& key, V && t)
     {
         for (auto it = this->begin(); it != this->end(); ++it)
         {
@@ -81,13 +83,14 @@ template <class Key, class T, class IgnoredLess = std::less<Key>,
                 return {it, false};
             }
         }
-        append(key, std::forward<T>(t));
+        append(key, std::forward<V>(t));
         return {std::prev(this->end()), true};
     }
 
-    template<class KeyType, detail::enable_if_t<
-                 detail::is_usable_as_key_type<key_compare, key_type, KeyType>::value, int> = 0>
-    std::pair<iterator, bool> emplace(KeyType && key, T && t)
+    template<class KeyType, class V, detail::enable_if_t<
+                 detail::conjunction<detail::is_usable_as_key_type<key_compare, key_type, KeyType>,
+                                     detail::is_constructible<T, V>>::value, int> = 0>
+    std::pair<iterator, bool> emplace(KeyType && key, V && t)
     {
         for (auto it = this->begin(); it != this->end(); ++it)
         {
@@ -96,7 +99,7 @@ template <class Key, class T, class IgnoredLess = std::less<Key>,
                 return {it, false};
             }
         }
-        append(std::forward<KeyType>(key), std::forward<T>(t));
+        append(std::forward<KeyType>(key), std::forward<V>(t));
         return {std::prev(this->end()), true};
     }
 

single_include/nlohmann/json.hpp

@@ -26622,7 +26622,9 @@ template <class Key, class T, class IgnoredLess = std::less<Key>,
         return *this;
     }
 
-    std::pair<iterator, bool> emplace(const key_type& key, T&& t)
+    template<class V, detail::enable_if_t<
+                 detail::is_constructible<T, V>::value, int> = 0>
+    std::pair<iterator, bool> emplace(const key_type& key, V && t)
     {
         for (auto it = this->begin(); it != this->end(); ++it)
         {
@@ -26631,13 +26633,14 @@ template <class Key, class T, class IgnoredLess = std::less<Key>,
                 return {it, false};
             }
         }
-        append(key, std::forward<T>(t));
+        append(key, std::forward<V>(t));
         return {std::prev(this->end()), true};
     }
 
-    template<class KeyType, detail::enable_if_t<
-                 detail::is_usable_as_key_type<key_compare, key_type, KeyType>::value, int> = 0>
-    std::pair<iterator, bool> emplace(KeyType && key, T && t)
+    template<class KeyType, class V, detail::enable_if_t<
+                 detail::conjunction<detail::is_usable_as_key_type<key_compare, key_type, KeyType>,
+                                     detail::is_constructible<T, V>>::value, int> = 0>
+    std::pair<iterator, bool> emplace(KeyType && key, V && t)
     {
         for (auto it = this->begin(); it != this->end(); ++it)
         {
@@ -26646,7 +26649,7 @@ template <class Key, class T, class IgnoredLess = std::less<Key>,
                 return {it, false};
             }
         }
-        append(std::forward<KeyType>(key), std::forward<T>(t));
+        append(std::forward<KeyType>(key), std::forward<V>(t));
         return {std::prev(this->end()), true};
     }
 
@@ -27931,38 +27934,18 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     using copy_scratch_value_t = std::pair<typename object_t::key_type, basic_json>;
     using copy_scratch_t = std::vector<copy_scratch_value_t, AllocatorType<copy_scratch_value_t>>;
 
-    /// @brief tag selecting the constructor below; used only to build the
-    /// elements of a deep copy (@ref copy_array_level, @ref copy_object_level)
-    struct copy_construct_tag {};
-
-  public:
-    /*!
-    @brief construct a null value whose base class - and, with @ref
-           JSON_DIAGNOSTIC_POSITIONS, positions - are copied from @a src
-
-    Copy-constructing @ref json_base_class_t here, rather than default-
-    constructing the element and assigning its base class afterwards, means
-    that copying a @ref basic_json only ever requires a copy-constructible
-    base class, and never a move-assignable one as well.
-
-    @note this constructor has to be public: @ref copy_array_level and
-          @ref copy_object_level reach it through @ref array_t's or @ref
-          object_t's own emplace_back(), which constructs the element from
-          outside @ref basic_json and so cannot call a private constructor.
-          @ref copy_construct_tag is private, though, and nothing in the
-          public interface hands out a value of it, so outside code can still
-          never name it to call this constructor itself.
-    */
-    basic_json(copy_construct_tag /*unused*/, const basic_json& src)
-        : json_base_class_t(src)
-#if JSON_DIAGNOSTIC_POSITIONS
-        , start_position(src.start_position)
-        , end_position(src.end_position)
-#endif
+    /// @brief copy everything of @a src into @a dst but its type and value
+    static void copy_metadata(const basic_json& src, basic_json& dst)
     {
-    }
+        // a custom base class is only required to be copy-constructible and
+        // move-assignable, so the copy has to go through a temporary
+        static_cast<json_base_class_t&>(dst) = json_base_class_t(static_cast<const json_base_class_t&>(src));
 
-  private:
+#if JSON_DIAGNOSTIC_POSITIONS
+        dst.start_position = src.start_position;
+        dst.end_position = src.end_position;
+#endif
+    }
 
     /*!
     @brief copy the value of @a src into @a dst, which must not be structured
@@ -28026,11 +28009,8 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     }
 
     /*!
-    @brief finish the copy @a dst of @a src that a @ref copy_construct_tag
-           constructor started, other than the children of an object or array
+    @brief copy everything of @a src into the null value @a dst but the children
 
-    @a dst already has @a src's base class and, with @ref
-    JSON_DIAGNOSTIC_POSITIONS, positions; only its value is still missing.
     Objects and arrays are not copied here; they are appended to @a worklist to
     be created later by @ref copy_iteratively. Until that happens, @a dst remains
     a null value, so that a partially built copy can be destroyed at any point
@@ -28038,6 +28018,8 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     */
     static void copy_shallow(const basic_json& src, basic_json& dst, copy_worklist_t& worklist)
     {
+        copy_metadata(src, dst);
+
         if (src.m_data.m_type == value_t::object || src.m_data.m_type == value_t::array)
         {
             // defer: dst stays a null value until its container exists
@@ -28058,19 +28040,15 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     {
         const array_t& src_array = *src.m_data.m_value.array;
 
+        // create all elements up front: growing the array afterwards could
+        // invalidate the pointers that are handed to the worklist; resize()
+        // rather than the fill constructor, because not every array type
+        // provides the latter (e.g., ones without a matching allocator-aware
+        // fill constructor)
         dst.m_data.m_value.array = create<array_t>();
         // only now that the array exists may dst stop being a null value
         dst.m_data.m_type = value_t::array;
-
-        // create every element - its base class already copy-constructed from
-        // its counterpart in src, via the copy_construct_tag constructor -
-        // before any of their addresses are handed to worklist below: growing
-        // the array while that is going on could reallocate it and invalidate
-        // addresses taken from an earlier iteration
-        for (const auto& src_element : src_array)
-        {
-            dst.m_data.m_value.array->emplace_back(copy_construct_tag{}, src_element);
-        }
+        dst.m_data.m_value.array->resize(src_array.size());
 
         auto dst_it = dst.m_data.m_value.array->begin();
         for (auto src_it = src_array.cbegin(); src_it != src_array.cend(); ++src_it, ++dst_it)
@@ -28088,14 +28066,12 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
 
         // build the complete key skeleton and hand it to the object's range
         // constructor: adding the keys one by one would be quadratic for object
-        // types that are backed by a vector, such as nlohmann::ordered_map; each
-        // value's base class is already copy-constructed from its counterpart
-        // in src, via the copy_construct_tag constructor
+        // types that are backed by a vector, such as nlohmann::ordered_map
         scratch.clear();
         scratch.reserve(src_object.size());
         for (const auto& element : src_object)
         {
-            scratch.emplace_back(element.first, basic_json(copy_construct_tag{}, element.second));
+            scratch.emplace_back(element.first, basic_json());
         }
 
         dst.m_data.m_value.object = create<object_t>(std::make_move_iterator(scratch.begin()),

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

@@ -405,73 +405,3 @@ TEST_CASE("JSON Visit Node")
         );
     CHECK(expected.empty());
 }
-
-// A custom base class with a const member: copy-constructible (initializing a
-// const member works fine), but not copy-/move-assignable (assigning one does
-// not). Used to check that copy construction never requires more than that.
-struct const_member_base
-{
-    const int id = 7; // NOLINT(misc-non-private-member-variables-in-classes)
-};
-
-using json_with_const_base = 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>,
-                             const_member_base
-                             >;
-
-// build an array nested @a depth levels deep, with the innermost value 1;
-// every level is constructed (never assigned), since const_member_base does
-// not support assignment
-static json_with_const_base make_nested_array(std::size_t depth)
-{
-    if (depth == 0)
-    {
-        return json_with_const_base(1);
-    }
-    return json_with_const_base::array({make_nested_array(depth - 1)});
-}
-
-TEST_CASE("Regression test for issue #5674 - copy construction must not require an assignable base class")
-{
-    SECTION("depth 0")
-    {
-        // as in the original bug report: copy construction only, no assignment
-        const json_with_const_base j = {1, 2};
-        const json_with_const_base copy = j; // NOLINT(performance-unnecessary-copy-initialization)
-
-        CHECK(copy.size() == 2);
-        CHECK(copy.id == 7);
-    }
-
-    SECTION("nested deeper than the copy constructor's descent bound")
-    {
-        // beyond nesting_depth_limit() (128) levels, the copy constructor
-        // copies without the call stack (copy_iteratively / copy_array_level),
-        // which used to assign the base class of every element it created
-        const std::size_t depth = 300;
-
-        const json_with_const_base j = make_nested_array(depth);
-        const json_with_const_base copy = j; // NOLINT(performance-unnecessary-copy-initialization)
-
-        const json_with_const_base* c = &copy;
-        for (std::size_t level = 0; level <= depth; ++level)
-        {
-            CAPTURE(level)
-            REQUIRE(c->id == 7);
-            if (level < depth)
-            {
-                c = &c->at(0);
-            }
-        }
-        CHECK(*c == 1);
-    }
-}

tests/src/unit-ordered_json.cpp

@@ -196,3 +196,44 @@ TEST_CASE("regression test - diff() must account for ordered_json member order")
         CHECK(a.patch(p) == b);
     }
 }
+
+TEST_CASE("regression test for issue #5673 - ordered_json::emplace with a non-rvalue value")
+{
+    SECTION("lvalue value")
+    {
+        ordered_json oj = ordered_json::object();
+        ordered_json value = 1;
+        auto res = oj.emplace("a", value);
+        CHECK(res.second == true);
+        CHECK(oj.dump() == "{\"a\":1}");
+    }
+
+    SECTION("const lvalue value")
+    {
+        ordered_json oj = ordered_json::object();
+        const ordered_json value = 1;
+        auto res = oj.emplace("a", value);
+        CHECK(res.second == true);
+        CHECK(oj.dump() == "{\"a\":1}");
+    }
+
+    SECTION("rvalue value")
+    {
+        ordered_json oj = ordered_json::object();
+        auto res = oj.emplace("a", ordered_json(1));
+        CHECK(res.second == true);
+        CHECK(oj.dump() == "{\"a\":1}");
+    }
+
+    SECTION("existing key is not overwritten (std::map-compatible semantics)")
+    {
+        ordered_json oj = ordered_json::object();
+        ordered_json value = 1;
+        oj.emplace("a", value);
+
+        ordered_json other_value = 2;
+        auto res = oj.emplace("a", other_value);
+        CHECK(res.second == false);
+        CHECK(oj.dump() == "{\"a\":1}");
+    }
+}

tests/src/unit-ordered_map.cpp

@@ -403,6 +403,79 @@ TEST_CASE("ordered_map")
             CHECK(om.size() == 4);
         }
     }
+
+    SECTION("emplace")
+    {
+        // regression test for issue #5673: the mapped-value parameter must
+        // accept lvalues and const lvalues, not just rvalues
+        ordered_map<std::string, std::string> om;
+        om["eins"] = "one";
+        om["zwei"] = "two";
+        om["drei"] = "three";
+
+        SECTION("with T&& (rvalue)")
+        {
+            auto res1 = om.emplace("eins", std::string("1"));
+            CHECK(res1.first == om.begin());
+            CHECK(res1.second == false);
+            CHECK(om.size() == 3);
+            CHECK(om.at("eins") == "one"); // existing key is not overwritten
+
+            auto res4 = om.emplace("vier", std::string("four"));
+            CHECK(res4.first == om.begin() + 3);
+            CHECK(res4.second == true);
+            CHECK(om.size() == 4);
+            CHECK(om.at("vier") == "four");
+        }
+
+        SECTION("with T& (lvalue)")
+        {
+            std::string one = "1";
+            std::string four = "four";
+
+            auto res1 = om.emplace("eins", one);
+            CHECK(res1.first == om.begin());
+            CHECK(res1.second == false);
+            CHECK(om.size() == 3);
+            CHECK(om.at("eins") == "one"); // existing key is not overwritten
+
+            auto res4 = om.emplace("vier", four);
+            CHECK(res4.first == om.begin() + 3);
+            CHECK(res4.second == true);
+            CHECK(om.size() == 4);
+            CHECK(om.at("vier") == "four");
+            CHECK(four == "four"); // source was copied, not moved from
+        }
+
+        SECTION("with const T&")
+        {
+            const std::string one = "1";
+            const std::string four = "four";
+
+            auto res1 = om.emplace("eins", one);
+            CHECK(res1.first == om.begin());
+            CHECK(res1.second == false);
+            CHECK(om.size() == 3);
+
+            auto res4 = om.emplace("vier", four);
+            CHECK(res4.first == om.begin() + 3);
+            CHECK(res4.second == true);
+            CHECK(om.size() == 4);
+            CHECK(om.at("vier") == "four");
+        }
+
+        SECTION("with key of key_type (non-template overload)")
+        {
+            const std::string key_vier{"vier"};
+            std::string four = "four";
+
+            auto res4 = om.emplace(key_vier, four);
+            CHECK(res4.first == om.begin() + 3);
+            CHECK(res4.second == true);
+            CHECK(om.size() == 4);
+            CHECK(om.at("vier") == "four");
+        }
+    }
 }
 
 TEST_CASE("ordered_map growth")