Merge branch 'develop' into claude/fix-allocation-exception-safety

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

docs/mkdocs/docs/api/basic_json/operator[].md

@@ -128,13 +128,10 @@ Strong exception safety: if an exception occurs, the original value stays intact
 
         When the JSON pointer traverses intermediate levels that don't exist at all yet (not just a missing
         leaf), each missing level is created as an array or an object depending on whether the corresponding
-        pointer token is a valid array index: the token `0`, a sequence of digits that does not begin with `0`,
-        or the token `-` creates an array, and every other token creates an object. For example, on an
-        initially `#!json null` value, `/foo/0/0/0` creates nested arrays, while `/foo/one/one/one` creates
-        nested objects. Tokens such as `01` or the empty token cannot be array indices (cf. RFC 6901, Sect. 4)
-        and therefore create objects, just as they would if the level already existed as an object. This is not
-        specified by the JSON Pointer RFC; it is this library's own, intentional disambiguation rule. See also
-        [JSON Pointer](../../features/json_pointer.md).
+        pointer token parses as a non-negative integer: a numeric token creates an array, a non-numeric token
+        creates an object. For example, on an initially `#!json null` value, `/foo/0/0/0` creates nested arrays,
+        while `/foo/one/one/one` creates nested objects. This is not specified by the JSON Pointer RFC; it is
+        this library's own, intentional disambiguation rule. See also [JSON Pointer](../../features/json_pointer.md).
 
 ## Examples
 

include/nlohmann/detail/conversions/to_json.hpp

@@ -42,6 +42,10 @@ namespace detail
  * j.m_data.m_value.destroy(j.m_data.m_type) to avoid a memory leak in case j contains an
  * allocated value (e.g., a string). See bug issue
  * https://github.com/nlohmann/json/issues/2865 for more information.
+ *
+ * A value that has to be allocated is created before the old one is destroyed:
+ * were it the other way around, an exception while creating the new value would
+ * leave j with the type of the new value, but the pointer to the destroyed old one.
  */
 
 template<value_t> struct external_constructor;
@@ -65,18 +69,20 @@ struct external_constructor<value_t::string>
     template<typename BasicJsonType>
     static void construct(BasicJsonType& j, const typename BasicJsonType::string_t& s)
     {
+        const typename BasicJsonType::json_value value(s);
         j.m_data.m_value.destroy(j.m_data.m_type);
         j.m_data.m_type = value_t::string;
-        j.m_data.m_value = s;
+        j.m_data.m_value = value;
         j.assert_invariant();
     }
 
     template<typename BasicJsonType>
     static void construct(BasicJsonType& j, typename BasicJsonType::string_t&& s)
     {
+        const typename BasicJsonType::json_value value(std::move(s));
         j.m_data.m_value.destroy(j.m_data.m_type);
         j.m_data.m_type = value_t::string;
-        j.m_data.m_value = std::move(s);
+        j.m_data.m_value = value;
         j.assert_invariant();
     }
 
@@ -85,9 +91,10 @@ struct external_constructor<value_t::string>
                              int > = 0 >
     static void construct(BasicJsonType& j, const CompatibleStringType& str)
     {
+        auto* created = j.template create<typename BasicJsonType::string_t>(str);
         j.m_data.m_value.destroy(j.m_data.m_type);
         j.m_data.m_type = value_t::string;
-        j.m_data.m_value.string = j.template create<typename BasicJsonType::string_t>(str);
+        j.m_data.m_value.string = created;
         j.assert_invariant();
     }
 };
@@ -98,18 +105,20 @@ struct external_constructor<value_t::binary>
     template<typename BasicJsonType>
     static void construct(BasicJsonType& j, const typename BasicJsonType::binary_t& b)
     {
+        const typename BasicJsonType::json_value value(b);
         j.m_data.m_value.destroy(j.m_data.m_type);
         j.m_data.m_type = value_t::binary;
-        j.m_data.m_value = typename BasicJsonType::binary_t(b);
+        j.m_data.m_value = value;
         j.assert_invariant();
     }
 
     template<typename BasicJsonType>
     static void construct(BasicJsonType& j, typename BasicJsonType::binary_t&& b)
     {
+        const typename BasicJsonType::json_value value(std::move(b));
         j.m_data.m_value.destroy(j.m_data.m_type);
         j.m_data.m_type = value_t::binary;
-        j.m_data.m_value = typename BasicJsonType::binary_t(std::move(b));
+        j.m_data.m_value = value;
         j.assert_invariant();
     }
 };
@@ -159,9 +168,10 @@ struct external_constructor<value_t::array>
     template<typename BasicJsonType>
     static void construct(BasicJsonType& j, const typename BasicJsonType::array_t& arr)
     {
+        const typename BasicJsonType::json_value value(arr);
         j.m_data.m_value.destroy(j.m_data.m_type);
         j.m_data.m_type = value_t::array;
-        j.m_data.m_value = arr;
+        j.m_data.m_value = value;
         j.set_parents();
         j.assert_invariant();
     }
@@ -169,9 +179,10 @@ struct external_constructor<value_t::array>
     template<typename BasicJsonType>
     static void construct(BasicJsonType& j, typename BasicJsonType::array_t&& arr)
     {
+        const typename BasicJsonType::json_value value(std::move(arr));
         j.m_data.m_value.destroy(j.m_data.m_type);
         j.m_data.m_type = value_t::array;
-        j.m_data.m_value = std::move(arr);
+        j.m_data.m_value = value;
         j.set_parents();
         j.assert_invariant();
     }
@@ -187,9 +198,10 @@ struct external_constructor<value_t::array>
         using std::begin;
         using std::end;
 
+        auto* created = j.template create<typename BasicJsonType::array_t>(begin(arr), end(arr));
         j.m_data.m_value.destroy(j.m_data.m_type);
         j.m_data.m_type = value_t::array;
-        j.m_data.m_value.array = j.template create<typename BasicJsonType::array_t>(begin(arr), end(arr));
+        j.m_data.m_value.array = created;
         j.set_parents();
         j.assert_invariant();
     }
@@ -197,15 +209,17 @@ struct external_constructor<value_t::array>
     template<typename BasicJsonType>
     static void construct(BasicJsonType& j, const std::vector<bool>& arr)
     {
-        j.m_data.m_value.destroy(j.m_data.m_type);
-        j.m_data.m_type = value_t::array;
-        j.m_data.m_value = value_t::array;
-        j.m_data.m_value.array->reserve(arr.size());
+        typename BasicJsonType::array_t elements;
+        elements.reserve(arr.size());
         for (const bool x : arr)
         {
-            j.m_data.m_value.array->push_back(x);
-            j.set_parent(j.m_data.m_value.array->back());
+            elements.push_back(x);
         }
+        const typename BasicJsonType::json_value value(std::move(elements));
+        j.m_data.m_value.destroy(j.m_data.m_type);
+        j.m_data.m_type = value_t::array;
+        j.m_data.m_value = value;
+        j.set_parents();
         j.assert_invariant();
     }
 
@@ -213,11 +227,12 @@ struct external_constructor<value_t::array>
              enable_if_t<std::is_convertible<T, BasicJsonType>::value, int> = 0>
     static void construct(BasicJsonType& j, const std::valarray<T>& arr)
     {
+        typename BasicJsonType::array_t elements(arr.size());
+        std::copy(std::begin(arr), std::end(arr), elements.begin());
+        const typename BasicJsonType::json_value value(std::move(elements));
         j.m_data.m_value.destroy(j.m_data.m_type);
         j.m_data.m_type = value_t::array;
-        j.m_data.m_value = value_t::array;
-        j.m_data.m_value.array->resize(arr.size());
-        std::copy(std::begin(arr), std::end(arr), j.m_data.m_value.array->begin());
+        j.m_data.m_value = value;
         j.set_parents();
         j.assert_invariant();
     }
@@ -229,14 +244,16 @@ struct external_constructor<value_t::array>
              enable_if_t<is_compatible_range_view<std::remove_cvref_t<CompatibleArrayType>>::value, int> = 0>
     static void construct(BasicJsonType& j, CompatibleArrayType && arr)
     {
-        j.m_data.m_value.destroy(j.m_data.m_type);
-        j.m_data.m_type = value_t::array;
-        j.m_data.m_value = value_t::array;
+        typename BasicJsonType::array_t elements;
         for (auto&& x : std::forward<CompatibleArrayType>(arr))
         {
-            j.m_data.m_value.array->push_back(x);
-            j.set_parent(j.m_data.m_value.array->back());
+            elements.push_back(x);
         }
+        const typename BasicJsonType::json_value value(std::move(elements));
+        j.m_data.m_value.destroy(j.m_data.m_type);
+        j.m_data.m_type = value_t::array;
+        j.m_data.m_value = value;
+        j.set_parents();
         j.assert_invariant();
     }
 #endif
@@ -248,9 +265,10 @@ struct external_constructor<value_t::object>
     template<typename BasicJsonType>
     static void construct(BasicJsonType& j, const typename BasicJsonType::object_t& obj)
     {
+        const typename BasicJsonType::json_value value(obj);
         j.m_data.m_value.destroy(j.m_data.m_type);
         j.m_data.m_type = value_t::object;
-        j.m_data.m_value = obj;
+        j.m_data.m_value = value;
         j.set_parents();
         j.assert_invariant();
     }
@@ -258,9 +276,10 @@ struct external_constructor<value_t::object>
     template<typename BasicJsonType>
     static void construct(BasicJsonType& j, typename BasicJsonType::object_t&& obj)
     {
+        const typename BasicJsonType::json_value value(std::move(obj));
         j.m_data.m_value.destroy(j.m_data.m_type);
         j.m_data.m_type = value_t::object;
-        j.m_data.m_value = std::move(obj);
+        j.m_data.m_value = value;
         j.set_parents();
         j.assert_invariant();
     }
@@ -272,9 +291,10 @@ struct external_constructor<value_t::object>
         using std::begin;
         using std::end;
 
+        auto* created = j.template create<typename BasicJsonType::object_t>(begin(obj), end(obj));
         j.m_data.m_value.destroy(j.m_data.m_type);
         j.m_data.m_type = value_t::object;
-        j.m_data.m_value.object = j.template create<typename BasicJsonType::object_t>(begin(obj), end(obj));
+        j.m_data.m_value.object = created;
         j.set_parents();
         j.assert_invariant();
     }

include/nlohmann/detail/json_pointer.hpp

@@ -416,19 +416,15 @@ class json_pointer
             // convert null values to arrays or objects before continuing
             if (ptr->is_null())
             {
-                // check if the reference token is a valid array index, that is
-                // a nonempty sequence of digits without a leading '0'
-                // (cf. RFC 6901, Sect. 4); tokens that could never be a valid
-                // array index (such as "01" or "") are treated as object keys
-                const bool nums = !reference_token.empty()
-                                  && (reference_token.size() == 1 || reference_token[0] != '0')
-                                  && std::all_of(reference_token.begin(), reference_token.end(),
-                                                 [](const unsigned char x)
+                // check if the reference token is a number
+                const bool nums =
+                    std::all_of(reference_token.begin(), reference_token.end(),
+                                [](const unsigned char x)
                 {
                     return std::isdigit(x);
                 });
 
-                // change value to an array for array indices or "-" or to object otherwise
+                // change value to an array for numbers or "-" or to object otherwise
                 *ptr = (nums || reference_token == "-")
                        ? detail::value_t::array
                        : detail::value_t::object;

include/nlohmann/json.hpp

@@ -1702,8 +1702,8 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         if (is_an_object)
         {
             // the initializer list is a list of pairs -> create an object
-            m_data.m_type = value_t::object;
             m_data.m_value = value_t::object;
+            m_data.m_type = value_t::object;
 
             for (auto& element_ref : init)
             {
@@ -1725,8 +1725,8 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
             }
 #endif
             // the initializer list describes an array -> create an array
-            m_data.m_type = value_t::array;
             m_data.m_value.array = create<array_t>(init.begin(), init.end());
+            m_data.m_type = value_t::array;
         }
 
         set_parents();
@@ -1739,8 +1739,8 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     static basic_json binary(const typename binary_t::container_type& init)
     {
         auto res = basic_json();
-        res.m_data.m_type = value_t::binary;
         res.m_data.m_value = init;
+        res.m_data.m_type = value_t::binary;
         return res;
     }
 
@@ -1750,8 +1750,8 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     static basic_json binary(const typename binary_t::container_type& init, typename binary_t::subtype_type subtype)
     {
         auto res = basic_json();
-        res.m_data.m_type = value_t::binary;
         res.m_data.m_value = binary_t(init, subtype);
+        res.m_data.m_type = value_t::binary;
         return res;
     }
 
@@ -1761,8 +1761,8 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     static basic_json binary(typename binary_t::container_type&& init)
     {
         auto res = basic_json();
-        res.m_data.m_type = value_t::binary;
         res.m_data.m_value = std::move(init);
+        res.m_data.m_type = value_t::binary;
         return res;
     }
 
@@ -1772,8 +1772,8 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     static basic_json binary(typename binary_t::container_type&& init, typename binary_t::subtype_type subtype)
     {
         auto res = basic_json();
-        res.m_data.m_type = value_t::binary;
         res.m_data.m_value = binary_t(std::move(init), subtype);
+        res.m_data.m_type = value_t::binary;
         return res;
     }
 
@@ -2819,8 +2819,8 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         // implicitly convert a null value to an empty array
         if (is_null())
         {
-            m_data.m_type = value_t::array;
             m_data.m_value.array = create<array_t>();
+            m_data.m_type = value_t::array;
             assert_invariant();
         }
 
@@ -2879,8 +2879,8 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         // implicitly convert a null value to an empty object
         if (is_null())
         {
-            m_data.m_type = value_t::object;
             m_data.m_value.object = create<object_t>();
+            m_data.m_type = value_t::object;
             assert_invariant();
         }
 
@@ -2932,8 +2932,8 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         // implicitly convert a null value to an empty object
         if (is_null())
         {
-            m_data.m_type = value_t::object;
             m_data.m_value.object = create<object_t>();
+            m_data.m_type = value_t::object;
             assert_invariant();
         }
 
@@ -3868,8 +3868,8 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         // transform a null object into an array
         if (is_null())
         {
-            m_data.m_type = value_t::array;
             m_data.m_value = value_t::array;
+            m_data.m_type = value_t::array;
             assert_invariant();
         }
 
@@ -3901,8 +3901,8 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         // transform a null object into an array
         if (is_null())
         {
-            m_data.m_type = value_t::array;
             m_data.m_value = value_t::array;
+            m_data.m_type = value_t::array;
             assert_invariant();
         }
 
@@ -3933,8 +3933,8 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         // transform a null object into an object
         if (is_null())
         {
-            m_data.m_type = value_t::object;
             m_data.m_value = value_t::object;
+            m_data.m_type = value_t::object;
             assert_invariant();
         }
 
@@ -3989,8 +3989,8 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         // transform a null object into an array
         if (is_null())
         {
-            m_data.m_type = value_t::array;
             m_data.m_value = value_t::array;
+            m_data.m_type = value_t::array;
             assert_invariant();
         }
 
@@ -4014,8 +4014,8 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         // transform a null object into an object
         if (is_null())
         {
-            m_data.m_type = value_t::object;
             m_data.m_value = value_t::object;
+            m_data.m_type = value_t::object;
             assert_invariant();
         }
 
@@ -4196,8 +4196,8 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         // implicitly convert a null value to an empty object
         if (is_null())
         {
-            m_data.m_type = value_t::object;
             m_data.m_value.object = create<object_t>();
+            m_data.m_type = value_t::object;
             assert_invariant();
         }
 

single_include/nlohmann/json.hpp

@@ -6571,6 +6571,10 @@ namespace detail
  * j.m_data.m_value.destroy(j.m_data.m_type) to avoid a memory leak in case j contains an
  * allocated value (e.g., a string). See bug issue
  * https://github.com/nlohmann/json/issues/2865 for more information.
+ *
+ * A value that has to be allocated is created before the old one is destroyed:
+ * were it the other way around, an exception while creating the new value would
+ * leave j with the type of the new value, but the pointer to the destroyed old one.
  */
 
 template<value_t> struct external_constructor;
@@ -6594,18 +6598,20 @@ struct external_constructor<value_t::string>
     template<typename BasicJsonType>
     static void construct(BasicJsonType& j, const typename BasicJsonType::string_t& s)
     {
+        const typename BasicJsonType::json_value value(s);
         j.m_data.m_value.destroy(j.m_data.m_type);
         j.m_data.m_type = value_t::string;
-        j.m_data.m_value = s;
+        j.m_data.m_value = value;
         j.assert_invariant();
     }
 
     template<typename BasicJsonType>
     static void construct(BasicJsonType& j, typename BasicJsonType::string_t&& s)
     {
+        const typename BasicJsonType::json_value value(std::move(s));
         j.m_data.m_value.destroy(j.m_data.m_type);
         j.m_data.m_type = value_t::string;
-        j.m_data.m_value = std::move(s);
+        j.m_data.m_value = value;
         j.assert_invariant();
     }
 
@@ -6614,9 +6620,10 @@ struct external_constructor<value_t::string>
                              int > = 0 >
     static void construct(BasicJsonType& j, const CompatibleStringType& str)
     {
+        auto* created = j.template create<typename BasicJsonType::string_t>(str);
         j.m_data.m_value.destroy(j.m_data.m_type);
         j.m_data.m_type = value_t::string;
-        j.m_data.m_value.string = j.template create<typename BasicJsonType::string_t>(str);
+        j.m_data.m_value.string = created;
         j.assert_invariant();
     }
 };
@@ -6627,18 +6634,20 @@ struct external_constructor<value_t::binary>
     template<typename BasicJsonType>
     static void construct(BasicJsonType& j, const typename BasicJsonType::binary_t& b)
     {
+        const typename BasicJsonType::json_value value(b);
         j.m_data.m_value.destroy(j.m_data.m_type);
         j.m_data.m_type = value_t::binary;
-        j.m_data.m_value = typename BasicJsonType::binary_t(b);
+        j.m_data.m_value = value;
         j.assert_invariant();
     }
 
     template<typename BasicJsonType>
     static void construct(BasicJsonType& j, typename BasicJsonType::binary_t&& b)
     {
+        const typename BasicJsonType::json_value value(std::move(b));
         j.m_data.m_value.destroy(j.m_data.m_type);
         j.m_data.m_type = value_t::binary;
-        j.m_data.m_value = typename BasicJsonType::binary_t(std::move(b));
+        j.m_data.m_value = value;
         j.assert_invariant();
     }
 };
@@ -6688,9 +6697,10 @@ struct external_constructor<value_t::array>
     template<typename BasicJsonType>
     static void construct(BasicJsonType& j, const typename BasicJsonType::array_t& arr)
     {
+        const typename BasicJsonType::json_value value(arr);
         j.m_data.m_value.destroy(j.m_data.m_type);
         j.m_data.m_type = value_t::array;
-        j.m_data.m_value = arr;
+        j.m_data.m_value = value;
         j.set_parents();
         j.assert_invariant();
     }
@@ -6698,9 +6708,10 @@ struct external_constructor<value_t::array>
     template<typename BasicJsonType>
     static void construct(BasicJsonType& j, typename BasicJsonType::array_t&& arr)
     {
+        const typename BasicJsonType::json_value value(std::move(arr));
         j.m_data.m_value.destroy(j.m_data.m_type);
         j.m_data.m_type = value_t::array;
-        j.m_data.m_value = std::move(arr);
+        j.m_data.m_value = value;
         j.set_parents();
         j.assert_invariant();
     }
@@ -6716,9 +6727,10 @@ struct external_constructor<value_t::array>
         using std::begin;
         using std::end;
 
+        auto* created = j.template create<typename BasicJsonType::array_t>(begin(arr), end(arr));
         j.m_data.m_value.destroy(j.m_data.m_type);
         j.m_data.m_type = value_t::array;
-        j.m_data.m_value.array = j.template create<typename BasicJsonType::array_t>(begin(arr), end(arr));
+        j.m_data.m_value.array = created;
         j.set_parents();
         j.assert_invariant();
     }
@@ -6726,15 +6738,17 @@ struct external_constructor<value_t::array>
     template<typename BasicJsonType>
     static void construct(BasicJsonType& j, const std::vector<bool>& arr)
     {
-        j.m_data.m_value.destroy(j.m_data.m_type);
-        j.m_data.m_type = value_t::array;
-        j.m_data.m_value = value_t::array;
-        j.m_data.m_value.array->reserve(arr.size());
+        typename BasicJsonType::array_t elements;
+        elements.reserve(arr.size());
         for (const bool x : arr)
         {
-            j.m_data.m_value.array->push_back(x);
-            j.set_parent(j.m_data.m_value.array->back());
+            elements.push_back(x);
         }
+        const typename BasicJsonType::json_value value(std::move(elements));
+        j.m_data.m_value.destroy(j.m_data.m_type);
+        j.m_data.m_type = value_t::array;
+        j.m_data.m_value = value;
+        j.set_parents();
         j.assert_invariant();
     }
 
@@ -6742,11 +6756,12 @@ struct external_constructor<value_t::array>
              enable_if_t<std::is_convertible<T, BasicJsonType>::value, int> = 0>
     static void construct(BasicJsonType& j, const std::valarray<T>& arr)
     {
+        typename BasicJsonType::array_t elements(arr.size());
+        std::copy(std::begin(arr), std::end(arr), elements.begin());
+        const typename BasicJsonType::json_value value(std::move(elements));
         j.m_data.m_value.destroy(j.m_data.m_type);
         j.m_data.m_type = value_t::array;
-        j.m_data.m_value = value_t::array;
-        j.m_data.m_value.array->resize(arr.size());
-        std::copy(std::begin(arr), std::end(arr), j.m_data.m_value.array->begin());
+        j.m_data.m_value = value;
         j.set_parents();
         j.assert_invariant();
     }
@@ -6758,14 +6773,16 @@ struct external_constructor<value_t::array>
              enable_if_t<is_compatible_range_view<std::remove_cvref_t<CompatibleArrayType>>::value, int> = 0>
     static void construct(BasicJsonType& j, CompatibleArrayType && arr)
     {
-        j.m_data.m_value.destroy(j.m_data.m_type);
-        j.m_data.m_type = value_t::array;
-        j.m_data.m_value = value_t::array;
+        typename BasicJsonType::array_t elements;
         for (auto&& x : std::forward<CompatibleArrayType>(arr))
         {
-            j.m_data.m_value.array->push_back(x);
-            j.set_parent(j.m_data.m_value.array->back());
+            elements.push_back(x);
         }
+        const typename BasicJsonType::json_value value(std::move(elements));
+        j.m_data.m_value.destroy(j.m_data.m_type);
+        j.m_data.m_type = value_t::array;
+        j.m_data.m_value = value;
+        j.set_parents();
         j.assert_invariant();
     }
 #endif
@@ -6777,9 +6794,10 @@ struct external_constructor<value_t::object>
     template<typename BasicJsonType>
     static void construct(BasicJsonType& j, const typename BasicJsonType::object_t& obj)
     {
+        const typename BasicJsonType::json_value value(obj);
         j.m_data.m_value.destroy(j.m_data.m_type);
         j.m_data.m_type = value_t::object;
-        j.m_data.m_value = obj;
+        j.m_data.m_value = value;
         j.set_parents();
         j.assert_invariant();
     }
@@ -6787,9 +6805,10 @@ struct external_constructor<value_t::object>
     template<typename BasicJsonType>
     static void construct(BasicJsonType& j, typename BasicJsonType::object_t&& obj)
     {
+        const typename BasicJsonType::json_value value(std::move(obj));
         j.m_data.m_value.destroy(j.m_data.m_type);
         j.m_data.m_type = value_t::object;
-        j.m_data.m_value = std::move(obj);
+        j.m_data.m_value = value;
         j.set_parents();
         j.assert_invariant();
     }
@@ -6801,9 +6820,10 @@ struct external_constructor<value_t::object>
         using std::begin;
         using std::end;
 
+        auto* created = j.template create<typename BasicJsonType::object_t>(begin(obj), end(obj));
         j.m_data.m_value.destroy(j.m_data.m_type);
         j.m_data.m_type = value_t::object;
-        j.m_data.m_value.object = j.template create<typename BasicJsonType::object_t>(begin(obj), end(obj));
+        j.m_data.m_value.object = created;
         j.set_parents();
         j.assert_invariant();
     }
@@ -19060,19 +19080,15 @@ class json_pointer
             // convert null values to arrays or objects before continuing
             if (ptr->is_null())
             {
-                // check if the reference token is a valid array index, that is
-                // a nonempty sequence of digits without a leading '0'
-                // (cf. RFC 6901, Sect. 4); tokens that could never be a valid
-                // array index (such as "01" or "") are treated as object keys
-                const bool nums = !reference_token.empty()
-                                  && (reference_token.size() == 1 || reference_token[0] != '0')
-                                  && std::all_of(reference_token.begin(), reference_token.end(),
-                                                 [](const unsigned char x)
+                // check if the reference token is a number
+                const bool nums =
+                    std::all_of(reference_token.begin(), reference_token.end(),
+                                [](const unsigned char x)
                 {
                     return std::isdigit(x);
                 });
 
-                // change value to an array for array indices or "-" or to object otherwise
+                // change value to an array for numbers or "-" or to object otherwise
                 *ptr = (nums || reference_token == "-")
                        ? detail::value_t::array
                        : detail::value_t::object;
@@ -27589,8 +27605,8 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         if (is_an_object)
         {
             // the initializer list is a list of pairs -> create an object
-            m_data.m_type = value_t::object;
             m_data.m_value = value_t::object;
+            m_data.m_type = value_t::object;
 
             for (auto& element_ref : init)
             {
@@ -27612,8 +27628,8 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
             }
 #endif
             // the initializer list describes an array -> create an array
-            m_data.m_type = value_t::array;
             m_data.m_value.array = create<array_t>(init.begin(), init.end());
+            m_data.m_type = value_t::array;
         }
 
         set_parents();
@@ -27626,8 +27642,8 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     static basic_json binary(const typename binary_t::container_type& init)
     {
         auto res = basic_json();
-        res.m_data.m_type = value_t::binary;
         res.m_data.m_value = init;
+        res.m_data.m_type = value_t::binary;
         return res;
     }
 
@@ -27637,8 +27653,8 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     static basic_json binary(const typename binary_t::container_type& init, typename binary_t::subtype_type subtype)
     {
         auto res = basic_json();
-        res.m_data.m_type = value_t::binary;
         res.m_data.m_value = binary_t(init, subtype);
+        res.m_data.m_type = value_t::binary;
         return res;
     }
 
@@ -27648,8 +27664,8 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     static basic_json binary(typename binary_t::container_type&& init)
     {
         auto res = basic_json();
-        res.m_data.m_type = value_t::binary;
         res.m_data.m_value = std::move(init);
+        res.m_data.m_type = value_t::binary;
         return res;
     }
 
@@ -27659,8 +27675,8 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     static basic_json binary(typename binary_t::container_type&& init, typename binary_t::subtype_type subtype)
     {
         auto res = basic_json();
-        res.m_data.m_type = value_t::binary;
         res.m_data.m_value = binary_t(std::move(init), subtype);
+        res.m_data.m_type = value_t::binary;
         return res;
     }
 
@@ -28706,8 +28722,8 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         // implicitly convert a null value to an empty array
         if (is_null())
         {
-            m_data.m_type = value_t::array;
             m_data.m_value.array = create<array_t>();
+            m_data.m_type = value_t::array;
             assert_invariant();
         }
 
@@ -28766,8 +28782,8 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         // implicitly convert a null value to an empty object
         if (is_null())
         {
-            m_data.m_type = value_t::object;
             m_data.m_value.object = create<object_t>();
+            m_data.m_type = value_t::object;
             assert_invariant();
         }
 
@@ -28819,8 +28835,8 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         // implicitly convert a null value to an empty object
         if (is_null())
         {
-            m_data.m_type = value_t::object;
             m_data.m_value.object = create<object_t>();
+            m_data.m_type = value_t::object;
             assert_invariant();
         }
 
@@ -29755,8 +29771,8 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         // transform a null object into an array
         if (is_null())
         {
-            m_data.m_type = value_t::array;
             m_data.m_value = value_t::array;
+            m_data.m_type = value_t::array;
             assert_invariant();
         }
 
@@ -29788,8 +29804,8 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         // transform a null object into an array
         if (is_null())
         {
-            m_data.m_type = value_t::array;
             m_data.m_value = value_t::array;
+            m_data.m_type = value_t::array;
             assert_invariant();
         }
 
@@ -29820,8 +29836,8 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         // transform a null object into an object
         if (is_null())
         {
-            m_data.m_type = value_t::object;
             m_data.m_value = value_t::object;
+            m_data.m_type = value_t::object;
             assert_invariant();
         }
 
@@ -29876,8 +29892,8 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         // transform a null object into an array
         if (is_null())
         {
-            m_data.m_type = value_t::array;
             m_data.m_value = value_t::array;
+            m_data.m_type = value_t::array;
             assert_invariant();
         }
 
@@ -29901,8 +29917,8 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         // transform a null object into an object
         if (is_null())
         {
-            m_data.m_type = value_t::object;
             m_data.m_value = value_t::object;
+            m_data.m_type = value_t::object;
             assert_invariant();
         }
 
@@ -30083,8 +30099,8 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         // implicitly convert a null value to an empty object
         if (is_null())
         {
-            m_data.m_type = value_t::object;
             m_data.m_value.object = create<object_t>();
+            m_data.m_type = value_t::object;
             assert_invariant();
         }
 

tests/src/unit-allocator.cpp

@@ -12,6 +12,11 @@
 #include <nlohmann/json.hpp>
 using nlohmann::json;
 
+#include <valarray>
+#if JSON_HAS_RANGES
+    #include <ranges>
+#endif
+
 namespace
 {
 // special test case to check if memory is leaked if constructor throws
@@ -394,3 +399,173 @@ TEST_CASE("bad my_allocator::construct")
         j["test"].push_back("should not leak");
     }
 }
+
+// the no-exceptions CI job skips every CHECK_THROWS_AS, which would leave
+// next_construct_fails set for the next allocation outside a check
+#if !defined(JSON_NOEXCEPTION)
+TEST_CASE("a failed allocation leaves the value unchanged")
+{
+    // create JSON type using the throwing allocator
+    using my_json = nlohmann::basic_json<std::map,
+          std::vector,
+          std::string,
+          bool,
+          std::int64_t,
+          std::uint64_t,
+          double,
+          my_allocator>;
+
+    // Each of these creates a string, array, object, or binary value. The
+    // value must be created before the type is changed: otherwise, a failed
+    // creation left a value of the new type without anything behind it (an
+    // assertion in its destructor, a null pointer everywhere else) or, when
+    // an old value was destroyed first, with a pointer to that destroyed one.
+
+    SECTION("creating a binary value")
+    {
+        const std::vector<std::uint8_t> bytes = {1, 2, 3};
+        my_json _;
+
+        next_construct_fails = true;
+        CHECK_THROWS_AS(_ = my_json::binary(bytes), std::bad_alloc&);
+        next_construct_fails = true;
+        CHECK_THROWS_AS(_ = my_json::binary(bytes, 42), std::bad_alloc&);
+        next_construct_fails = true;
+        CHECK_THROWS_AS(_ = my_json::binary(std::vector<std::uint8_t>(bytes)), std::bad_alloc&);
+        next_construct_fails = true;
+        CHECK_THROWS_AS(_ = my_json::binary(std::vector<std::uint8_t>(bytes), 42), std::bad_alloc&);
+        next_construct_fails = false;
+    }
+
+    SECTION("turning a null value into an array or object")
+    {
+        my_json j;
+
+        next_construct_fails = true;
+        CHECK_THROWS_AS(j[0], std::bad_alloc&);
+        CHECK(j.is_null());
+
+        next_construct_fails = true;
+        CHECK_THROWS_AS(j["key"], std::bad_alloc&);
+        CHECK(j.is_null());
+
+#ifdef JSON_HAS_CPP_17
+        next_construct_fails = true;
+        CHECK_THROWS_AS(j[std::string_view("key")], std::bad_alloc&);
+        CHECK(j.is_null());
+#endif
+
+        next_construct_fails = true;
+        CHECK_THROWS_AS(j.push_back(my_json(1)), std::bad_alloc&);
+        CHECK(j.is_null());
+
+        const my_json one = 1;
+        next_construct_fails = true;
+        CHECK_THROWS_AS(j.push_back(one), std::bad_alloc&);
+        CHECK(j.is_null());
+
+        next_construct_fails = true;
+        CHECK_THROWS_AS(j.push_back(my_json::object_t::value_type("key", 1)), std::bad_alloc&);
+        CHECK(j.is_null());
+
+        next_construct_fails = true;
+        CHECK_THROWS_AS(j.emplace_back(1), std::bad_alloc&);
+        CHECK(j.is_null());
+
+        next_construct_fails = true;
+        CHECK_THROWS_AS(j.emplace("key", 1), std::bad_alloc&);
+        CHECK(j.is_null());
+
+        const my_json object = {{"key", 1}};
+        next_construct_fails = true;
+        CHECK_THROWS_AS(j.update(object), std::bad_alloc&);
+        CHECK(j.is_null());
+
+        next_construct_fails = false;
+    }
+
+    SECTION("converting into an existing value")
+    {
+        // to_json replaces the value it is given; the old one must survive a
+        // failed creation of the new one
+        my_json j = "old";
+
+        next_construct_fails = true;
+        CHECK_THROWS_AS(nlohmann::to_json(j, std::string("new")), std::bad_alloc&);
+        CHECK(j == "old");
+
+        next_construct_fails = true;
+        CHECK_THROWS_AS(nlohmann::to_json(j, std::vector<int> {1, 2}), std::bad_alloc&);
+        CHECK(j == "old");
+
+        // with iterator debugging, the default constructor of VS 2015's
+        // std::vector is noexcept but constructs a proxy with the allocator,
+        // which terminates when this allocator throws
+#if !(defined(_MSC_VER) && _MSC_VER < 1910 && defined(_ITERATOR_DEBUG_LEVEL) && _ITERATOR_DEBUG_LEVEL > 0)
+        next_construct_fails = true;
+        CHECK_THROWS_AS(nlohmann::to_json(j, std::vector<bool> {true, false}), std::bad_alloc&);
+        CHECK(j == "old");
+#endif
+
+        next_construct_fails = true;
+        CHECK_THROWS_AS(nlohmann::to_json(j, std::map<std::string, int> {{"a", 1}}), std::bad_alloc&);
+        CHECK(j == "old");
+
+        next_construct_fails = true;
+        CHECK_THROWS_AS(nlohmann::to_json(j, my_json::binary_t({1, 2})), std::bad_alloc&);
+        CHECK(j == "old");
+
+        // the overloads for lvalues of the value types, for the value types
+        // themselves, and for the remaining compatible types
+        const std::string string = "new";
+        next_construct_fails = true;
+        CHECK_THROWS_AS(nlohmann::to_json(j, string), std::bad_alloc&);
+        CHECK(j == "old");
+
+        next_construct_fails = true;
+        CHECK_THROWS_AS(nlohmann::to_json(j, "new"), std::bad_alloc&);
+        CHECK(j == "old");
+
+        // to_json only moves a binary value that it converted from another
+        // container type, which my_json's std::vector<std::uint8_t> is not
+        using binary_constructor = nlohmann::detail::external_constructor<nlohmann::detail::value_t::binary>;
+        next_construct_fails = true;
+        CHECK_THROWS_AS(binary_constructor::construct(j, my_json::binary_t({1, 2})), std::bad_alloc&);
+        CHECK(j == "old");
+
+        my_json::array_t array = {1, 2};
+        next_construct_fails = true;
+        CHECK_THROWS_AS(nlohmann::to_json(j, array), std::bad_alloc&);
+        CHECK(j == "old");
+        next_construct_fails = true;
+        CHECK_THROWS_AS(nlohmann::to_json(j, std::move(array)), std::bad_alloc&);
+        CHECK(j == "old");
+
+        my_json::object_t object = {{"a", 1}};
+        next_construct_fails = true;
+        CHECK_THROWS_AS(nlohmann::to_json(j, object), std::bad_alloc&);
+        CHECK(j == "old");
+        next_construct_fails = true;
+        CHECK_THROWS_AS(nlohmann::to_json(j, std::move(object)), std::bad_alloc&);
+        CHECK(j == "old");
+
+        next_construct_fails = true;
+        CHECK_THROWS_AS(nlohmann::to_json(j, std::valarray<int> {1, 2}), std::bad_alloc&);
+        CHECK(j == "old");
+
+#if JSON_HAS_RANGES && !defined(__MINGW32__)
+        const std::vector<int> numbers = {1, 2};
+        next_construct_fails = true;
+        CHECK_THROWS_AS(nlohmann::to_json(j, numbers | std::views::filter([](int /*unused*/)
+        {
+            return true;
+        })), std::bad_alloc&);
+        CHECK(j == "old");
+#endif
+
+        next_construct_fails = false;
+        nlohmann::to_json(j, std::vector<int> {1, 2});
+        CHECK(j == my_json({1, 2}));
+    }
+}
+#endif

tests/src/unit-json_pointer.cpp

@@ -438,72 +438,6 @@ TEST_CASE("JSON pointers")
         }
     }
 
-    SECTION("creating intermediate levels")
-    {
-        SECTION("tokens that are valid array indices create arrays")
-        {
-            json j;
-            j["/0"_json_pointer] = 1;
-            CHECK(j == json({1}));
-
-            json j2;
-            j2["/2"_json_pointer] = 1;
-            CHECK(j2 == json({nullptr, nullptr, 1}));
-
-            json j3;
-            j3["/-"_json_pointer] = 1;
-            CHECK(j3 == json({1}));
-
-            json j4;
-            j4["/foo/0/0"_json_pointer] = 1;
-            CHECK(j4 == json({{"foo", {{1}}}}));
-        }
-
-        SECTION("tokens that are no valid array indices create objects")
-        {
-            json j;
-            j["/one"_json_pointer] = 1;
-            CHECK(j == json({{"one", 1}}));
-
-            // leading '0' can never be a valid array index (RFC 6901, Sect. 4)
-            json j2;
-            j2["/01"_json_pointer] = 1;
-            CHECK(j2 == json({{"01", 1}}));
-
-            // the empty token is a valid object key, but no valid array index
-            json j3;
-            j3["/"_json_pointer] = 1;
-            CHECK(j3 == json({{"", 1}}));
-        }
-
-        SECTION("creating a level yields the same result as reusing it (#5357)")
-        {
-            json j;
-            j["/a/b/01/d"_json_pointer] = "value";
-
-            json j_init = json::object();
-            j_init["/a/b"_json_pointer] = json::object();
-            j_init["/a/b/01/d"_json_pointer] = "value";
-
-            const json expected = json::parse(R"({"a":{"b":{"01":{"d":"value"}}}})");
-            CHECK(j == expected);
-            CHECK(j_init == expected);
-
-            // unflatten uses the same key
-            const json flat = {{"/a/b/01/d", "value"}};
-            CHECK(flat.unflatten() == expected);
-        }
-
-        SECTION("existing arrays still reject invalid indices")
-        {
-            json j = {1, 2, 3};
-            CHECK_THROWS_WITH_AS(j["/01"_json_pointer],
-                                 "[json.exception.parse_error.106] parse error: array index '01' must not begin with '0'", json::parse_error&);
-            CHECK_THROWS_WITH_AS(j.at("/01"_json_pointer),
-                                 "[json.exception.parse_error.106] parse error: array index '01' must not begin with '0'", json::parse_error&);
-        }
-    }
-
     SECTION("flatten")
     {
         json j =