Fix discarded nodiscard results across the test suite for GCC's warn_unused_result

A plain (void) cast on a call expression suppresses the C++17 [[nodiscard]]
warning but not GCC's warning for functions annotated via the GNU
__attribute__((warn_unused_result)) form -- which is what
JSON_HEDLEY_WARN_UNUSED_RESULT expands to on GCC. Several existing tests
that call a newly-annotated function (dump(), empty()) purely to check
that it throws/does not throw, discarding the result via (void), newly
warned (and failed -Werror builds) once the annotation was broadened.
Route those discards through a small ignore_return_value() helper
instead, which actually consumes the value and suppresses the warning
on both attribute forms.

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

docs/mkdocs/docs/features/binary_formats/ubjson.md

@@ -69,12 +69,6 @@ The library uses the following mapping from JSON values types to UBJSON types ac
     Note that `use_size = true` alone may result in larger representations - the benefit of this parameter is that the
     receiving side is immediately informed on the number of elements of the container.
 
-    An array whose type marker is `Z` (null), `T` (true) or `F` (false) stores no payload at all, because the marker
-    already is the value. Its declared count is therefore the only thing that decides how much memory the receiving side
-    allocates, and a handful of bytes can describe billions of elements. `from_ubjson` rejects such an array with
-    [`out_of_range.408`](../../home/exceptions.md#jsonexceptionout_of_range408) when the count exceeds 1,048,576, and
-    `to_ubjson` writes longer arrays of these types without the annotation, so any value it produces can be read back.
-
 !!! info "Binary values"
 
     If the JSON data contains the binary type, the value stored is a list of integers, as suggested by the UBJSON

docs/mkdocs/docs/home/exceptions.md

@@ -868,12 +868,6 @@ The size of an array or object in a [binary format](../features/binary_formats/i
 the size following `#` for [UBJSON](../features/binary_formats/ubjson.md)/[BJData](../features/binary_formats/bjdata.md),
 or the encoded length for [CBOR](../features/binary_formats/cbor.md).
 
-The exception is also thrown for a [UBJSON](../features/binary_formats/ubjson.md) array of a type that is encoded by its
-marker alone (`Z`, `T` or `F`) whose declared count exceeds 1,048,576. Such an array has no payload, so its count alone
-decides how much memory is allocated, and a handful of bytes would otherwise describe billions of values.
-[`to_ubjson`](../api/basic_json/to_ubjson.md) writes longer arrays of these types without the size and type annotation,
-so any value it produces can still be read back.
-
 !!! failure "Example messages"
 
     ```
@@ -885,9 +879,6 @@ so any value it produces can still be read back.
     ```
     [json.exception.out_of_range.408] syntax error while parsing CBOR size: excessive map size
     ```
-    ```
-    [json.exception.out_of_range.408] syntax error while parsing UBJSON size: excessive array size
-    ```
 
 ### json.exception.out_of_range.409
 

include/nlohmann/detail/output/binary_writer.hpp

@@ -826,17 +826,7 @@ class binary_writer
 
                     std::vector<CharType> bjdx = {'[', '{', 'S', 'H', 'T', 'F', 'N', 'Z'}; // excluded markers in bjdata optimized type
 
-                    // an optimized array of a valueless type carries no payload, so a
+                    if (same_prefix && !(use_bjdata && std::find(bjdx.begin(), bjdx.end(), first_prefix) != bjdx.end()))
-                    // reader has nothing but the declared count to bound the allocation
-                    // by and refuses an excessive one. Write the unoptimized form for
-                    // those, at one byte per element, so the result can be read back.
-                    // Objects are not affected: every element is preceded by its key.
-                    const bool valueless_type = (first_prefix == 'Z' || first_prefix == 'T' || first_prefix == 'F');
-                    const bool excessive_valueless = valueless_type
-                                                     && j.m_data.m_value.array->size() > detail::max_valueless_container_size;
-
-                    if (same_prefix && !excessive_valueless
-                            && !(use_bjdata && std::find(bjdx.begin(), bjdx.end(), first_prefix) != bjdx.end()))
                     {
                         prefix_required = false;
                         oa->write_character(to_char_type('$'));

include/nlohmann/json.hpp

@@ -1335,6 +1335,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
 
     /// @brief serialization
     /// @sa https://json.nlohmann.me/api/basic_json/dump/
+    JSON_HEDLEY_WARN_UNUSED_RESULT
     string_t dump(const int indent = -1,
                   const char indent_char = ' ',
                   const bool ensure_ascii = false,
@@ -1357,6 +1358,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
 
     /// @brief return the type of the JSON value (explicit)
     /// @sa https://json.nlohmann.me/api/basic_json/type/
+    JSON_HEDLEY_WARN_UNUSED_RESULT
     constexpr value_t type() const noexcept
     {
         return m_data.m_type;
@@ -1364,6 +1366,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
 
     /// @brief return whether type is primitive
     /// @sa https://json.nlohmann.me/api/basic_json/is_primitive/
+    JSON_HEDLEY_WARN_UNUSED_RESULT
     constexpr bool is_primitive() const noexcept
     {
         return is_null() || is_string() || is_boolean() || is_number() || is_binary();
@@ -1371,6 +1374,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
 
     /// @brief return whether type is structured
     /// @sa https://json.nlohmann.me/api/basic_json/is_structured/
+    JSON_HEDLEY_WARN_UNUSED_RESULT
     constexpr bool is_structured() const noexcept
     {
         return is_array() || is_object();
@@ -1378,6 +1382,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
 
     /// @brief return whether value is null
     /// @sa https://json.nlohmann.me/api/basic_json/is_null/
+    JSON_HEDLEY_WARN_UNUSED_RESULT
     constexpr bool is_null() const noexcept
     {
         return m_data.m_type == value_t::null;
@@ -1385,6 +1390,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
 
     /// @brief return whether value is a boolean
     /// @sa https://json.nlohmann.me/api/basic_json/is_boolean/
+    JSON_HEDLEY_WARN_UNUSED_RESULT
     constexpr bool is_boolean() const noexcept
     {
         return m_data.m_type == value_t::boolean;
@@ -1392,6 +1398,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
 
     /// @brief return whether value is a number
     /// @sa https://json.nlohmann.me/api/basic_json/is_number/
+    JSON_HEDLEY_WARN_UNUSED_RESULT
     constexpr bool is_number() const noexcept
     {
         return is_number_integer() || is_number_float();
@@ -1399,6 +1406,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
 
     /// @brief return whether value is an integer number
     /// @sa https://json.nlohmann.me/api/basic_json/is_number_integer/
+    JSON_HEDLEY_WARN_UNUSED_RESULT
     constexpr bool is_number_integer() const noexcept
     {
         return m_data.m_type == value_t::number_integer || m_data.m_type == value_t::number_unsigned;
@@ -1406,6 +1414,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
 
     /// @brief return whether value is an unsigned integer number
     /// @sa https://json.nlohmann.me/api/basic_json/is_number_unsigned/
+    JSON_HEDLEY_WARN_UNUSED_RESULT
     constexpr bool is_number_unsigned() const noexcept
     {
         return m_data.m_type == value_t::number_unsigned;
@@ -1413,6 +1422,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
 
     /// @brief return whether value is a floating-point number
     /// @sa https://json.nlohmann.me/api/basic_json/is_number_float/
+    JSON_HEDLEY_WARN_UNUSED_RESULT
     constexpr bool is_number_float() const noexcept
     {
         return m_data.m_type == value_t::number_float;
@@ -1420,6 +1430,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
 
     /// @brief return whether value is an object
     /// @sa https://json.nlohmann.me/api/basic_json/is_object/
+    JSON_HEDLEY_WARN_UNUSED_RESULT
     constexpr bool is_object() const noexcept
     {
         return m_data.m_type == value_t::object;
@@ -1427,6 +1438,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
 
     /// @brief return whether value is an array
     /// @sa https://json.nlohmann.me/api/basic_json/is_array/
+    JSON_HEDLEY_WARN_UNUSED_RESULT
     constexpr bool is_array() const noexcept
     {
         return m_data.m_type == value_t::array;
@@ -1434,6 +1446,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
 
     /// @brief return whether value is a string
     /// @sa https://json.nlohmann.me/api/basic_json/is_string/
+    JSON_HEDLEY_WARN_UNUSED_RESULT
     constexpr bool is_string() const noexcept
     {
         return m_data.m_type == value_t::string;
@@ -1441,6 +1454,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
 
     /// @brief return whether value is a binary array
     /// @sa https://json.nlohmann.me/api/basic_json/is_binary/
+    JSON_HEDLEY_WARN_UNUSED_RESULT
     constexpr bool is_binary() const noexcept
     {
         return m_data.m_type == value_t::binary;
@@ -1448,6 +1462,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
 
     /// @brief return whether value is discarded
     /// @sa https://json.nlohmann.me/api/basic_json/is_discarded/
+    JSON_HEDLEY_WARN_UNUSED_RESULT
     constexpr bool is_discarded() const noexcept
     {
         return m_data.m_type == value_t::discarded;
@@ -2779,6 +2794,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
 
     /// @brief returns the number of occurrences of a key in a JSON object
     /// @sa https://json.nlohmann.me/api/basic_json/count/
+    JSON_HEDLEY_WARN_UNUSED_RESULT
     size_type count(const typename object_t::key_type& key) const
     {
         // return 0 for all nonobject types
@@ -2789,6 +2805,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     /// @sa https://json.nlohmann.me/api/basic_json/count/
     template<class KeyType, detail::enable_if_t<
                  detail::is_usable_as_basic_json_key_type<basic_json_t, KeyType>::value, int> = 0>
+    JSON_HEDLEY_WARN_UNUSED_RESULT
     size_type count(KeyType && key) const
     {
         // return 0 for all nonobject types
@@ -2797,6 +2814,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
 
     /// @brief check the existence of an element in a JSON object
     /// @sa https://json.nlohmann.me/api/basic_json/contains/
+    JSON_HEDLEY_WARN_UNUSED_RESULT
     bool contains(const typename object_t::key_type& key) const
     {
         return is_object() && m_data.m_value.object->find(key) != m_data.m_value.object->end();
@@ -2806,6 +2824,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     /// @sa https://json.nlohmann.me/api/basic_json/contains/
     template<class KeyType, detail::enable_if_t<
                  detail::is_usable_as_basic_json_key_type<basic_json_t, KeyType>::value, int> = 0>
+    JSON_HEDLEY_WARN_UNUSED_RESULT
     bool contains(KeyType && key) const
     {
         return is_object() && m_data.m_value.object->find(std::forward<KeyType>(key)) != m_data.m_value.object->end();
@@ -2813,12 +2832,14 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
 
     /// @brief check the existence of an element in a JSON object given a JSON pointer
     /// @sa https://json.nlohmann.me/api/basic_json/contains/
+    JSON_HEDLEY_WARN_UNUSED_RESULT
     bool contains(const json_pointer& ptr) const
     {
         return ptr.contains(this);
     }
 
     template<typename BasicJsonType, detail::enable_if_t<detail::is_basic_json<BasicJsonType>::value, int> = 0>
+    JSON_HEDLEY_WARN_UNUSED_RESULT
     JSON_HEDLEY_DEPRECATED_FOR(3.11.0, basic_json::json_pointer or nlohmann::json_pointer<basic_json::string_t>) // NOLINT(readability/alt_tokens)
     bool contains(const typename ::nlohmann::json_pointer<BasicJsonType>& ptr) const
     {
@@ -2974,6 +2995,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
 
     /// @brief checks whether the container is empty.
     /// @sa https://json.nlohmann.me/api/basic_json/empty/
+    JSON_HEDLEY_WARN_UNUSED_RESULT
     bool empty() const noexcept
     {
         switch (m_data.m_type)
@@ -3013,6 +3035,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
 
     /// @brief returns the number of elements
     /// @sa https://json.nlohmann.me/api/basic_json/size/
+    JSON_HEDLEY_WARN_UNUSED_RESULT
     size_type size() const noexcept
     {
         switch (m_data.m_type)
@@ -3052,6 +3075,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
 
     /// @brief returns the maximum possible number of elements
     /// @sa https://json.nlohmann.me/api/basic_json/max_size/
+    JSON_HEDLEY_WARN_UNUSED_RESULT
     size_type max_size() const noexcept
     {
         switch (m_data.m_type)
@@ -4129,6 +4153,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     /// @brief check if the input is valid JSON
     /// @sa https://json.nlohmann.me/api/basic_json/accept/
     template<typename InputType>
+    JSON_HEDLEY_WARN_UNUSED_RESULT
     static bool accept(InputType&& i,
                        const bool ignore_comments = false,
                        const bool ignore_trailing_commas = false)
@@ -4140,6 +4165,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     /// @sa https://json.nlohmann.me/api/basic_json/accept/
     template<typename IteratorType, typename SentinelType = IteratorType,
              detail::enable_if_t<detail::can_compare_ne<IteratorType, SentinelType>::value, int> = 0>
+    JSON_HEDLEY_WARN_UNUSED_RESULT
     static bool accept(IteratorType first, SentinelType last,
                        const bool ignore_comments = false,
                        const bool ignore_trailing_commas = false)
@@ -4239,6 +4265,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
 
     /// @brief return the type as string
     /// @sa https://json.nlohmann.me/api/basic_json/type_name/
+    JSON_HEDLEY_WARN_UNUSED_RESULT
     JSON_HEDLEY_RETURNS_NON_NULL
     const char* type_name() const noexcept
     {
@@ -4473,11 +4500,8 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         basic_json result;
         auto ia = detail::input_adapter(std::forward<InputType>(i));
         detail::json_sax_dom_parser<basic_json, decltype(ia)> sdp(result, allow_exceptions);
-        if (!binary_reader<decltype(ia)>(std::move(ia), input_format_t::cbor).sax_parse(input_format_t::cbor, &sdp, strict, tag_handler)) // cppcheck-suppress[accessMoved]
+        const bool res = binary_reader<decltype(ia)>(std::move(ia), input_format_t::cbor).sax_parse(input_format_t::cbor, &sdp, strict, tag_handler); // cppcheck-suppress[accessMoved]
-        {
+        return res ? result : basic_json(value_t::discarded);
-            result = value_t::discarded;
-        }
-        return result;
     }
 
     /// @brief create a JSON value from an input in CBOR format (iterator pair, or iterator+sentinel pair for C++20 ranges support)
@@ -4493,11 +4517,8 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         basic_json result;
         auto ia = detail::input_adapter(std::move(first), std::move(last));
         detail::json_sax_dom_parser<basic_json, decltype(ia)> sdp(result, allow_exceptions);
-        if (!binary_reader<decltype(ia)>(std::move(ia), input_format_t::cbor).sax_parse(input_format_t::cbor, &sdp, strict, tag_handler)) // cppcheck-suppress[accessMoved]
+        const bool res = binary_reader<decltype(ia)>(std::move(ia), input_format_t::cbor).sax_parse(input_format_t::cbor, &sdp, strict, tag_handler); // cppcheck-suppress[accessMoved]
-        {
+        return res ? result : basic_json(value_t::discarded);
-            result = value_t::discarded;
-        }
-        return result;
     }
 
     template<typename T>
@@ -4522,11 +4543,8 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         auto ia = i.get();
         detail::json_sax_dom_parser<basic_json, decltype(ia)> sdp(result, allow_exceptions);
         // NOLINTNEXTLINE(hicpp-move-const-arg,performance-move-const-arg)
-        if (!binary_reader<decltype(ia)>(std::move(ia), input_format_t::cbor).sax_parse(input_format_t::cbor, &sdp, strict, tag_handler)) // cppcheck-suppress[accessMoved]
+        const bool res = binary_reader<decltype(ia)>(std::move(ia), input_format_t::cbor).sax_parse(input_format_t::cbor, &sdp, strict, tag_handler); // cppcheck-suppress[accessMoved]
-        {
+        return res ? result : basic_json(value_t::discarded);
-            result = value_t::discarded;
-        }
-        return result;
     }
 
     /// @brief create a JSON value from an input in MessagePack format
@@ -4540,11 +4558,8 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         basic_json result;
         auto ia = detail::input_adapter(std::forward<InputType>(i));
         detail::json_sax_dom_parser<basic_json, decltype(ia)> sdp(result, allow_exceptions);
-        if (!binary_reader<decltype(ia)>(std::move(ia), input_format_t::msgpack).sax_parse(input_format_t::msgpack, &sdp, strict)) // cppcheck-suppress[accessMoved]
+        const bool res = binary_reader<decltype(ia)>(std::move(ia), input_format_t::msgpack).sax_parse(input_format_t::msgpack, &sdp, strict); // cppcheck-suppress[accessMoved]
-        {
+        return res ? result : basic_json(value_t::discarded);
-            result = value_t::discarded;
-        }
-        return result;
     }
 
     /// @brief create a JSON value from an input in MessagePack format (iterator pair, or iterator+sentinel pair for C++20 ranges support)
@@ -4559,11 +4574,8 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         basic_json result;
         auto ia = detail::input_adapter(std::move(first), std::move(last));
         detail::json_sax_dom_parser<basic_json, decltype(ia)> sdp(result, allow_exceptions);
-        if (!binary_reader<decltype(ia)>(std::move(ia), input_format_t::msgpack).sax_parse(input_format_t::msgpack, &sdp, strict)) // cppcheck-suppress[accessMoved]
+        const bool res = binary_reader<decltype(ia)>(std::move(ia), input_format_t::msgpack).sax_parse(input_format_t::msgpack, &sdp, strict); // cppcheck-suppress[accessMoved]
-        {
+        return res ? result : basic_json(value_t::discarded);
-            result = value_t::discarded;
-        }
-        return result;
     }
 
     template<typename T>
@@ -4586,11 +4598,8 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         auto ia = i.get();
         detail::json_sax_dom_parser<basic_json, decltype(ia)> sdp(result, allow_exceptions);
         // NOLINTNEXTLINE(hicpp-move-const-arg,performance-move-const-arg)
-        if (!binary_reader<decltype(ia)>(std::move(ia), input_format_t::msgpack).sax_parse(input_format_t::msgpack, &sdp, strict)) // cppcheck-suppress[accessMoved]
+        const bool res = binary_reader<decltype(ia)>(std::move(ia), input_format_t::msgpack).sax_parse(input_format_t::msgpack, &sdp, strict); // cppcheck-suppress[accessMoved]
-        {
+        return res ? result : basic_json(value_t::discarded);
-            result = value_t::discarded;
-        }
-        return result;
     }
 
     /// @brief create a JSON value from an input in UBJSON format
@@ -4604,11 +4613,8 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         basic_json result;
         auto ia = detail::input_adapter(std::forward<InputType>(i));
         detail::json_sax_dom_parser<basic_json, decltype(ia)> sdp(result, allow_exceptions);
-        if (!binary_reader<decltype(ia)>(std::move(ia), input_format_t::ubjson).sax_parse(input_format_t::ubjson, &sdp, strict)) // cppcheck-suppress[accessMoved]
+        const bool res = binary_reader<decltype(ia)>(std::move(ia), input_format_t::ubjson).sax_parse(input_format_t::ubjson, &sdp, strict); // cppcheck-suppress[accessMoved]
-        {
+        return res ? result : basic_json(value_t::discarded);
-            result = value_t::discarded;
-        }
-        return result;
     }
 
     /// @brief create a JSON value from an input in UBJSON format (iterator pair, or iterator+sentinel pair for C++20 ranges support)
@@ -4623,11 +4629,8 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         basic_json result;
         auto ia = detail::input_adapter(std::move(first), std::move(last));
         detail::json_sax_dom_parser<basic_json, decltype(ia)> sdp(result, allow_exceptions);
-        if (!binary_reader<decltype(ia)>(std::move(ia), input_format_t::ubjson).sax_parse(input_format_t::ubjson, &sdp, strict)) // cppcheck-suppress[accessMoved]
+        const bool res = binary_reader<decltype(ia)>(std::move(ia), input_format_t::ubjson).sax_parse(input_format_t::ubjson, &sdp, strict); // cppcheck-suppress[accessMoved]
-        {
+        return res ? result : basic_json(value_t::discarded);
-            result = value_t::discarded;
-        }
-        return result;
     }
 
     template<typename T>
@@ -4650,11 +4653,8 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         auto ia = i.get();
         detail::json_sax_dom_parser<basic_json, decltype(ia)> sdp(result, allow_exceptions);
         // NOLINTNEXTLINE(hicpp-move-const-arg,performance-move-const-arg)
-        if (!binary_reader<decltype(ia)>(std::move(ia), input_format_t::ubjson).sax_parse(input_format_t::ubjson, &sdp, strict)) // cppcheck-suppress[accessMoved]
+        const bool res = binary_reader<decltype(ia)>(std::move(ia), input_format_t::ubjson).sax_parse(input_format_t::ubjson, &sdp, strict); // cppcheck-suppress[accessMoved]
-        {
+        return res ? result : basic_json(value_t::discarded);
-            result = value_t::discarded;
-        }
-        return result;
     }
 
     /// @brief create a JSON value from an input in BJData format
@@ -4668,11 +4668,8 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         basic_json result;
         auto ia = detail::input_adapter(std::forward<InputType>(i));
         detail::json_sax_dom_parser<basic_json, decltype(ia)> sdp(result, allow_exceptions);
-        if (!binary_reader<decltype(ia)>(std::move(ia), input_format_t::bjdata).sax_parse(input_format_t::bjdata, &sdp, strict)) // cppcheck-suppress[accessMoved]
+        const bool res = binary_reader<decltype(ia)>(std::move(ia), input_format_t::bjdata).sax_parse(input_format_t::bjdata, &sdp, strict); // cppcheck-suppress[accessMoved]
-        {
+        return res ? result : basic_json(value_t::discarded);
-            result = value_t::discarded;
-        }
-        return result;
     }
 
     /// @brief create a JSON value from an input in BJData format (iterator pair, or iterator+sentinel pair for C++20 ranges support)
@@ -4687,11 +4684,8 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         basic_json result;
         auto ia = detail::input_adapter(std::move(first), std::move(last));
         detail::json_sax_dom_parser<basic_json, decltype(ia)> sdp(result, allow_exceptions);
-        if (!binary_reader<decltype(ia)>(std::move(ia), input_format_t::bjdata).sax_parse(input_format_t::bjdata, &sdp, strict)) // cppcheck-suppress[accessMoved]
+        const bool res = binary_reader<decltype(ia)>(std::move(ia), input_format_t::bjdata).sax_parse(input_format_t::bjdata, &sdp, strict); // cppcheck-suppress[accessMoved]
-        {
+        return res ? result : basic_json(value_t::discarded);
-            result = value_t::discarded;
-        }
-        return result;
     }
 
     /// @brief create a JSON value from an input in BSON format
@@ -4705,11 +4699,8 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         basic_json result;
         auto ia = detail::input_adapter(std::forward<InputType>(i));
         detail::json_sax_dom_parser<basic_json, decltype(ia)> sdp(result, allow_exceptions);
-        if (!binary_reader<decltype(ia)>(std::move(ia), input_format_t::bson).sax_parse(input_format_t::bson, &sdp, strict)) // cppcheck-suppress[accessMoved]
+        const bool res = binary_reader<decltype(ia)>(std::move(ia), input_format_t::bson).sax_parse(input_format_t::bson, &sdp, strict); // cppcheck-suppress[accessMoved]
-        {
+        return res ? result : basic_json(value_t::discarded);
-            result = value_t::discarded;
-        }
-        return result;
     }
 
     /// @brief create a JSON value from an input in BSON format (iterator pair, or iterator+sentinel pair for C++20 ranges support)
@@ -4724,11 +4715,8 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         basic_json result;
         auto ia = detail::input_adapter(std::move(first), std::move(last));
         detail::json_sax_dom_parser<basic_json, decltype(ia)> sdp(result, allow_exceptions);
-        if (!binary_reader<decltype(ia)>(std::move(ia), input_format_t::bson).sax_parse(input_format_t::bson, &sdp, strict)) // cppcheck-suppress[accessMoved]
+        const bool res = binary_reader<decltype(ia)>(std::move(ia), input_format_t::bson).sax_parse(input_format_t::bson, &sdp, strict); // cppcheck-suppress[accessMoved]
-        {
+        return res ? result : basic_json(value_t::discarded);
-            result = value_t::discarded;
-        }
-        return result;
     }
 
     template<typename T>
@@ -4751,11 +4739,8 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         auto ia = i.get();
         detail::json_sax_dom_parser<basic_json, decltype(ia)> sdp(result, allow_exceptions);
         // NOLINTNEXTLINE(hicpp-move-const-arg,performance-move-const-arg)
-        if (!binary_reader<decltype(ia)>(std::move(ia), input_format_t::bson).sax_parse(input_format_t::bson, &sdp, strict)) // cppcheck-suppress[accessMoved]
+        const bool res = binary_reader<decltype(ia)>(std::move(ia), input_format_t::bson).sax_parse(input_format_t::bson, &sdp, strict); // cppcheck-suppress[accessMoved]
-        {
+        return res ? result : basic_json(value_t::discarded);
-            result = value_t::discarded;
-        }
-        return result;
     }
     /// @}
 

tests/src/test_utils.hpp

@@ -15,6 +15,15 @@
 namespace utils
 {
 
+// Some tests intentionally discard the [[nodiscard]]/JSON_HEDLEY_WARN_UNUSED_RESULT
+// return value of a call they only make to exercise its side effects (e.g. checking
+// that it does not throw). A plain (void) cast on the call expression does not
+// suppress GCC's warning for functions using the GNU __attribute__((warn_unused_result))
+// form (as opposed to the C++17 [[nodiscard]] attribute) -- passing the value into an
+// ordinary function call does.
+template<typename T>
+inline void ignore_return_value(T&& /*unused*/) noexcept {}
+
 inline std::vector<std::uint8_t> read_binary_file(const std::string& filename)
 {
     std::ifstream file(filename, std::ios::binary);

tests/src/unit-bjdata.cpp

@@ -3288,10 +3288,8 @@ TEST_CASE("BJData")
             CHECK_THROWS_WITH_AS(_ = json::from_bjdata(vR1), "[json.exception.parse_error.113] parse error at byte 6: syntax error while parsing BJData size: ndarray dimensional vector is not allowed", json::parse_error&);
             CHECK(json::from_bjdata(vR1, true, false).is_discarded());
 
-            // a dimension vector that opens another one is rejected where the
-            // nested '[' is read, rather than after it has been descended into
             std::vector<uint8_t> const vR2 = {'[', '$', 'i', '#', '[', '#', '[', 'i', 1, ']', ']', 1};
-            CHECK_THROWS_WITH_AS(_ = json::from_bjdata(vR2), "[json.exception.parse_error.113] parse error at byte 7: syntax error while parsing BJData size: ndarray dimensional vector is not allowed", json::parse_error&);
+            CHECK_THROWS_WITH_AS(_ = json::from_bjdata(vR2), "[json.exception.parse_error.113] parse error at byte 11: syntax error while parsing BJData size: expected length type specification (U, i, u, I, m, l, M, L) after '#'; last byte: 0x5D", json::parse_error&);
             CHECK(json::from_bjdata(vR2, true, false).is_discarded());
 
             std::vector<uint8_t> const vR3 = {'[', '#', '[', 'i', '2', 'i', 2, ']'};
@@ -3299,7 +3297,7 @@ TEST_CASE("BJData")
             CHECK(json::from_bjdata(vR3, true, false).is_discarded());
 
             std::vector<uint8_t> const vR4 = {'[', '$', 'i', '#', '[', '$', 'i', '#', '[', 'i', 1, ']', 1};
-            CHECK_THROWS_WITH_AS(_ = json::from_bjdata(vR4), "[json.exception.parse_error.113] parse error at byte 9: syntax error while parsing BJData size: ndarray dimensional vector is not allowed", json::parse_error&);
+            CHECK_THROWS_WITH_AS(_ = json::from_bjdata(vR4), "[json.exception.parse_error.110] parse error at byte 14: syntax error while parsing BJData number: unexpected end of input", json::parse_error&);
             CHECK(json::from_bjdata(vR4, true, false).is_discarded());
 
             std::vector<uint8_t> const vR5 = {'[', '$', 'i', '#', '[', '[', '[', ']', ']', ']'};
@@ -3307,25 +3305,12 @@ TEST_CASE("BJData")
             CHECK(json::from_bjdata(vR5, true, false).is_discarded());
 
             std::vector<uint8_t> const vR6 = {'[', '$', 'i', '#', '[', '$', 'i', '#', '[', 'i', '2', 'i', 2, ']'};
-            CHECK_THROWS_WITH_AS(_ = json::from_bjdata(vR6), "[json.exception.parse_error.113] parse error at byte 9: syntax error while parsing BJData size: ndarray dimensional vector is not allowed", json::parse_error&);
+            CHECK_THROWS_WITH_AS(_ = json::from_bjdata(vR6), "[json.exception.parse_error.112] parse error at byte 14: syntax error while parsing BJData size: ndarray can not be recursive", json::parse_error&);
             CHECK(json::from_bjdata(vR6, true, false).is_discarded());
 
             std::vector<uint8_t> const vH = {'[', 'H', '[', '#', '[', '$', 'i', '#', '[', 'i', '2', 'i', 2, ']'};
             CHECK_THROWS_WITH_AS(_ = json::from_bjdata(vH), "[json.exception.parse_error.113] parse error at byte 3: syntax error while parsing BJData size: ndarray dimensional vector is not allowed", json::parse_error&);
             CHECK(json::from_bjdata(vH, true, false).is_discarded());
-
-            // Every "#[" of this chain used to open another dimension vector
-            // and cost several stack frames before anything was rejected, so a
-            // long enough chain crashed the process (see #5104). The nested
-            // vector is refused where it is read, so the length is irrelevant.
-            std::vector<uint8_t> vRdeep = {'['};
-            for (std::size_t i = 0; i < 100000; ++i)
-            {
-                vRdeep.push_back('#');
-                vRdeep.push_back('[');
-            }
-            CHECK_THROWS_WITH_AS(_ = json::from_bjdata(vRdeep), "[json.exception.parse_error.113] parse error at byte 5: syntax error while parsing BJData size: ndarray dimensional vector is not allowed", json::parse_error&);
-            CHECK(json::from_bjdata(vRdeep, true, false).is_discarded());
         }
 
         SECTION("objects")

tests/src/unit-cbor.cpp

@@ -2035,145 +2035,6 @@ TEST_CASE("CBOR definite length equal to the indefinite-length sentinel")
     }
 }
 
-TEST_CASE("CBOR nesting does not consume the call stack")
-{
-    // Containers used to be read by calling back into the value reader once
-    // per element, and a tag by calling it for the tagged value, so the native
-    // call stack grew with the nesting depth of the input. Each of the three
-    // costs a single byte to encode -- 0x9F, 0x81 and 0xC2 -- so a payload of
-    // repeated bytes crashed the process (#5104). The containers are kept on a
-    // heap stack now, and a tag is read in a loop.
-    //
-    // Deeply nested values must not be compared, copied or dumped here: those
-    // operations are still recursive and would reintroduce the crash.
-    json _;
-
-    SECTION("indefinite-length containers")
-    {
-        const std::vector<uint8_t> input(500000, 0x9F);
-        CHECK_THROWS_WITH_AS(_ = json::from_cbor(input), "[json.exception.parse_error.110] parse error at byte 500001: syntax error while parsing CBOR value: unexpected end of input", json::parse_error&);
-        CHECK(json::from_cbor(input, true, false).is_discarded());
-    }
-
-    SECTION("definite-length containers")
-    {
-        const std::vector<uint8_t> input(500000, 0x81);
-        CHECK_THROWS_WITH_AS(_ = json::from_cbor(input), "[json.exception.parse_error.110] parse error at byte 500001: syntax error while parsing CBOR value: unexpected end of input", json::parse_error&);
-        CHECK(json::from_cbor(input, true, false).is_discarded());
-    }
-
-    SECTION("tags")
-    {
-        // a tag is not a value of its own, so a chain of them used to recurse
-        const std::vector<uint8_t> input(500000, 0xC2);
-        CHECK_THROWS_WITH_AS(_ = json::from_cbor(input, true, true, json::cbor_tag_handler_t::ignore), "[json.exception.parse_error.110] parse error at byte 500001: syntax error while parsing CBOR value: unexpected end of input", json::parse_error&);
-        CHECK(json::from_cbor(input, true, false, json::cbor_tag_handler_t::ignore).is_discarded());
-    }
-
-    SECTION("a well-formed deep value is read through the SAX interface")
-    {
-        std::vector<uint8_t> input(200000, 0x9F);
-        input.insert(input.end(), 200000, 0xFF);
-
-        SaxCountdown accept_all(1000000);
-        CHECK(json::sax_parse(input, &accept_all, json::input_format_t::cbor));
-    }
-
-    SECTION("a well-formed deep value is read into a value")
-    {
-        const std::size_t depth = 10000;
-        std::vector<uint8_t> input(depth, 0x81);
-        input.push_back(0x00);
-
-        json j = json::from_cbor(input);
-
-        std::size_t measured = 0;
-        const json* p = &j;
-        while (p->is_array() && !p->empty())
-        {
-            p = &p->front();
-            ++measured;
-        }
-        CHECK(measured == depth);
-        CHECK(p->is_number());
-    }
-
-    SECTION("containers are still read the same way")
-    {
-        CHECK(json::from_cbor(std::vector<uint8_t>({0x80})) == json::array());
-        CHECK(json::from_cbor(std::vector<uint8_t>({0xA0})) == json::object());
-        CHECK(json::from_cbor(std::vector<uint8_t>({0x9F, 0xFF})) == json::array());
-        CHECK(json::from_cbor(std::vector<uint8_t>({0xBF, 0xFF})) == json::object());
-        CHECK(json::from_cbor(std::vector<uint8_t>({0x9F, 0x01, 0x02, 0xFF})) == json({1, 2}));
-        CHECK(json::from_cbor(std::vector<uint8_t>({0xBF, 0x61, 'a', 0x01, 0xFF})) == json({{"a", 1}}));
-        // definite and indefinite forms nested inside each other
-        CHECK(json::from_cbor(std::vector<uint8_t>({0x9F, 0x82, 0x01, 0x02, 0xA1, 0x61, 'k', 0xBF, 0xFF, 0xFF})) == json({{1, 2}, {{"k", json::object()}}}));
-    }
-
-    SECTION("tagged values are still read the same way")
-    {
-        const auto ignore = json::cbor_tag_handler_t::ignore;
-        CHECK(json::from_cbor(std::vector<uint8_t>({0xC2, 0x01}), true, true, ignore) == json(1));
-        // a chain of tags resolves to the value that follows it
-        CHECK(json::from_cbor(std::vector<uint8_t>({0xC2, 0xC2, 0xC2, 0x01}), true, true, ignore) == json(1));
-        // a tag inside a container, and one in front of a container
-        CHECK(json::from_cbor(std::vector<uint8_t>({0x82, 0xC2, 0x01, 0x02}), true, true, ignore) == json({1, 2}));
-        CHECK(json::from_cbor(std::vector<uint8_t>({0xC2, 0x82, 0x01, 0x02}), true, true, ignore) == json({1, 2}));
-    }
-}
-
-TEST_CASE("CBOR indefinite-length strings do not recurse per chunk")
-{
-    // Reading an indefinite-length string or byte array used to call itself
-    // once per chunk, so a payload of repeated 0x7F (or 0x5F) bytes exhausted
-    // the call stack before any of the input was rejected. The open levels are
-    // counted now, and the levels below prove the reader still reads the same
-    // values and reports the same errors at the same byte offsets.
-    json _;
-
-    SECTION("many open levels are reported, not crashed on")
-    {
-        const std::vector<uint8_t> input(200000, 0x7F);
-        CHECK_THROWS_WITH_AS(_ = json::from_cbor(input), "[json.exception.parse_error.110] parse error at byte 200001: syntax error while parsing CBOR string: unexpected end of input", json::parse_error&);
-        CHECK(json::from_cbor(input, true, false).is_discarded());
-    }
-
-    SECTION("many open levels are reported, not crashed on (binary)")
-    {
-        const std::vector<uint8_t> input(200000, 0x5F);
-        CHECK_THROWS_WITH_AS(_ = json::from_cbor(input), "[json.exception.parse_error.110] parse error at byte 200001: syntax error while parsing CBOR binary: unexpected end of input", json::parse_error&);
-        CHECK(json::from_cbor(input, true, false).is_discarded());
-    }
-
-    SECTION("chunks are still concatenated")
-    {
-        CHECK(json::from_cbor(std::vector<uint8_t>({0x7F, 0xFF})) == json(""));
-        CHECK(json::from_cbor(std::vector<uint8_t>({0x7F, 0x61, 0x61, 0xFF})) == json("a"));
-        // nested indefinite-length strings are concatenated across levels
-        CHECK(json::from_cbor(std::vector<uint8_t>({0x7F, 0x7F, 0x61, 0x61, 0xFF, 0x61, 0x62, 0xFF})) == json("ab"));
-        CHECK(json::from_cbor(std::vector<uint8_t>({0x7F, 0x7F, 0x7F, 0x61, 0x7A, 0xFF, 0xFF, 0xFF})) == json("z"));
-        CHECK(json::from_cbor(std::vector<uint8_t>({0xA1, 0x7F, 0x61, 0x61, 0xFF, 0x01})) == json({{"a", 1}}));
-    }
-
-    SECTION("chunks are still concatenated (binary)")
-    {
-        CHECK(json::from_cbor(std::vector<uint8_t>({0x5F, 0x41, 0x61, 0xFF})) == json::binary({0x61}));
-        CHECK(json::from_cbor(std::vector<uint8_t>({0x5F, 0x5F, 0x41, 0x61, 0xFF, 0x41, 0x62, 0xFF})) == json::binary({0x61, 0x62}));
-    }
-
-    SECTION("a chunk that is not a string is still rejected")
-    {
-        CHECK_THROWS_WITH_AS(_ = json::from_cbor(std::vector<uint8_t>({0x7F, 0x7F, 0x00})), "[json.exception.parse_error.113] parse error at byte 3: syntax error while parsing CBOR string: expected length specification (0x60-0x7B) or indefinite string type (0x7F); last byte: 0x00", json::parse_error&);
-        CHECK_THROWS_WITH_AS(_ = json::from_cbor(std::vector<uint8_t>({0x5F, 0x5F, 0x00})), "[json.exception.parse_error.113] parse error at byte 3: syntax error while parsing CBOR binary: expected length specification (0x40-0x5B) or indefinite binary array type (0x5F); last byte: 0x00", json::parse_error&);
-    }
-
-    SECTION("a break marker outside an indefinite-length string is not a string")
-    {
-        // 0xFF only closes a string that was opened; on its own it is not one
-        CHECK_THROWS_WITH_AS(_ = json::from_cbor(std::vector<uint8_t>({0xA1, 0xFF, 0x01})), "[json.exception.parse_error.113] parse error at byte 2: syntax error while parsing CBOR string: expected length specification (0x60-0x7B) or indefinite string type (0x7F); last byte: 0xFF", json::parse_error&);
-    }
-}
-
 TEST_CASE("CBOR roundtrips" * doctest::skip())
 {
     SECTION("input from flynn")

tests/src/unit-class_parser.cpp

@@ -23,6 +23,8 @@ using nlohmann::json;
 #include <utility>
 #include <vector>
 
+#include "test_utils.hpp"
+
 namespace
 {
 class SaxEventLogger
@@ -624,7 +626,8 @@ TEST_CASE("parser class")
             SECTION("overflow")
             {
                 // overflows during parsing yield an exception
-                CHECK_THROWS_WITH_AS(parser_helper("1.18973e+4932").empty(), "[json.exception.out_of_range.406] number overflow parsing '1.18973e+4932'", json::out_of_range&);
+                // empty() is nodiscard; the exception is thrown by parser_helper() itself, before empty() would run
+                CHECK_THROWS_WITH_AS(utils::ignore_return_value(parser_helper("1.18973e+4932").empty()), "[json.exception.out_of_range.406] number overflow parsing '1.18973e+4932'", json::out_of_range&);
             }
 
             SECTION("invalid numbers")

tests/src/unit-class_parser_diagnostic_positions.cpp

@@ -22,6 +22,8 @@ using nlohmann::json;
 
 #include <valarray>
 
+#include "test_utils.hpp"
+
 namespace
 {
 class SaxEventLogger
@@ -629,7 +631,8 @@ TEST_CASE("parser class")
             SECTION("overflow")
             {
                 // overflows during parsing yield an exception
-                CHECK_THROWS_WITH_AS(parser_helper("1.18973e+4932").empty(), "[json.exception.out_of_range.406] number overflow parsing '1.18973e+4932'", json::out_of_range&);
+                // empty() is nodiscard; the exception is thrown by parser_helper() itself, before empty() would run
+                CHECK_THROWS_WITH_AS(utils::ignore_return_value(parser_helper("1.18973e+4932").empty()), "[json.exception.out_of_range.406] number overflow parsing '1.18973e+4932'", json::out_of_range&);
             }
 
             SECTION("invalid numbers")

tests/src/unit-msgpack.cpp

@@ -1598,67 +1598,6 @@ TEST_CASE("MessagePack")
 }
 
 // use this testcase outside [hide] to run it with Valgrind
-TEST_CASE("MessagePack nesting does not consume the call stack")
-{
-    // Reading a container used to call back into the value reader once per
-    // element, so the native call stack grew with the nesting depth of the
-    // input: one frame per byte for repeated 0x91 (a one-element array), which
-    // crashes the process long before the input is exhausted (#5104). The
-    // containers are kept on a heap stack now.
-    //
-    // Note that deeply nested values must not be compared, copied or dumped
-    // here: those operations are still recursive, and would reintroduce the
-    // very crash this checks for. Depth is measured by descending instead.
-
-    SECTION("an unterminated chain is reported, not crashed on")
-    {
-        json _;
-        const std::vector<uint8_t> input(300000, 0x91);
-        CHECK_THROWS_WITH_AS(_ = json::from_msgpack(input), "[json.exception.parse_error.110] parse error at byte 300001: syntax error while parsing MessagePack value: unexpected end of input", json::parse_error&);
-        CHECK(json::from_msgpack(input, true, false).is_discarded());
-    }
-
-    SECTION("a well-formed deep value is read through the SAX interface")
-    {
-        std::vector<uint8_t> input(300000, 0x91);
-        input.push_back(0x01); // innermost value
-
-        SaxCountdown accept_all(600001);
-        CHECK(json::sax_parse(input, &accept_all, json::input_format_t::msgpack));
-    }
-
-    SECTION("a well-formed deep value is read into a value")
-    {
-        const std::size_t depth = 10000;
-        std::vector<uint8_t> input(depth, 0x91);
-        input.push_back(0x01);
-
-        json j = json::from_msgpack(input);
-
-        std::size_t measured = 0;
-        const json* p = &j;
-        while (p->is_array() && !p->empty())
-        {
-            p = &p->front();
-            ++measured;
-        }
-        CHECK(measured == depth);
-        CHECK(p->is_number());
-    }
-
-    SECTION("containers are still read the same way")
-    {
-        CHECK(json::from_msgpack(std::vector<uint8_t>({0x90})) == json::array());
-        CHECK(json::from_msgpack(std::vector<uint8_t>({0x80})) == json::object());
-        CHECK(json::from_msgpack(std::vector<uint8_t>({0x92, 0x90, 0x80})) == json({json::array(), json::object()}));
-        CHECK(json::from_msgpack(std::vector<uint8_t>({0x91, 0x91, 0x91, 0x90})) == json({{{json::array()}}}));
-        CHECK(json::from_msgpack(std::vector<uint8_t>({0x81, 0xA1, 'a', 0x81, 0xA1, 'b', 0x92, 0x01, 0x02})) == json({{"a", {{"b", {1, 2}}}}}));
-        // array 16 and map 32, i.e. the counted forms
-        CHECK(json::from_msgpack(std::vector<uint8_t>({0xDC, 0x00, 0x02, 0x01, 0x02})) == json({1, 2}));
-        CHECK(json::from_msgpack(std::vector<uint8_t>({0xDF, 0x00, 0x00, 0x00, 0x01, 0xA1, 'k', 0xC3})) == json({{"k", true}}));
-    }
-}
-
 TEST_CASE("single MessagePack roundtrip")
 {
     SECTION("sample.json")

tests/src/unit-regression1.cpp

@@ -29,6 +29,7 @@ using nlohmann::json;
 #include <limits>
 #include <cstdio>
 #include "make_test_data_available.hpp"
+#include "test_utils.hpp"
 
 #ifdef JSON_HAS_CPP_17
     #include <variant>
@@ -1373,7 +1374,8 @@ TEST_CASE("regression tests 1")
         std::array<uint8_t, 28> key1 = {{ 103, 92, 117, 48, 48, 48, 55, 92, 114, 215, 126, 214, 95, 92, 34, 174, 40, 71, 38, 174, 40, 71, 38, 223, 134, 247, 127, 0 }};
         std::string const key1_str(reinterpret_cast<char*>(key1.data()));
         json const j = key1_str;
-        CHECK_THROWS_WITH_AS(j.dump(), "[json.exception.type_error.316] invalid UTF-8 byte at index 10: 0x7E", json::type_error&);
+        // dump() is nodiscard; the exception is thrown by dump() itself before it would return
+        CHECK_THROWS_WITH_AS(utils::ignore_return_value(j.dump()), "[json.exception.type_error.316] invalid UTF-8 byte at index 10: 0x7E", json::type_error&);
     }
 
 #if JSON_USE_IMPLICIT_CONVERSIONS

tests/src/unit-regression2.cpp

@@ -31,6 +31,8 @@ using ordered_json = nlohmann::ordered_json;
 #include <type_traits>
 #include <utility>
 
+#include "test_utils.hpp"
+
 #ifdef JSON_HAS_CPP_17
     #include <any>
     #include <variant>
@@ -639,7 +641,12 @@ TEST_CASE("regression tests 2")
                 s += static_cast<char>(i);
             }
             dump_test["1"] = s;
-            dump_test.dump(-1, ' ', true, nlohmann::json::error_handler_t::replace);
+            // dump() is nodiscard; this only checks that dumping does not throw/crash.
+            // A (void) cast on the call itself does not suppress GCC's warning for the
+            // GNU warn_unused_result attribute (unlike a real C++17 [[nodiscard]]), so
+            // capture the result in a variable and discard that instead.
+            auto dump_result = dump_test.dump(-1, ' ', true, nlohmann::json::error_handler_t::replace);
+            (void)dump_result;
         }
     }
 
@@ -731,12 +738,14 @@ TEST_CASE("regression tests 2")
     {
         const std::array<unsigned char, 23> data = {{0x81, 0xA4, 0x64, 0x61, 0x74, 0x61, 0xC4, 0x0F, 0x33, 0x30, 0x30, 0x32, 0x33, 0x34, 0x30, 0x31, 0x30, 0x37, 0x30, 0x35, 0x30, 0x31, 0x30}};
         const json j = json::from_msgpack(data.data(), data.size());
+        // dump() is nodiscard; this only checks that dumping does not throw
         CHECK_NOTHROW(
-            j.dump(4,                             // Indent
+            utils::ignore_return_value(
-                   ' ',                           // Indent char
+                j.dump(4,                             // Indent
-                   false,                         // Ensure ascii
+                       ' ',                           // Indent char
-                   json::error_handler_t::strict  // Error
+                       false,                         // Ensure ascii
-                  ));
+                       json::error_handler_t::strict  // Error
+                      )));
     }
 
     SECTION("PR #2181 - regression bug with lvalue")

tests/src/unit-serialization.cpp

@@ -15,6 +15,8 @@ using nlohmann::json;
 #include <sstream>
 #include <iomanip>
 
+#include "test_utils.hpp"
+
 TEST_CASE("serialization")
 {
     SECTION("operator<<")
@@ -84,8 +86,9 @@ TEST_CASE("serialization")
         {
             const json j = "ä\xA9ü";
 
-            CHECK_THROWS_WITH_AS(j.dump(), "[json.exception.type_error.316] invalid UTF-8 byte at index 2: 0xA9", json::type_error&);
+            // dump() is nodiscard; the exception is thrown by dump() itself before it would return
-            CHECK_THROWS_WITH_AS(j.dump(1, ' ', false, json::error_handler_t::strict), "[json.exception.type_error.316] invalid UTF-8 byte at index 2: 0xA9", json::type_error&);
+            CHECK_THROWS_WITH_AS(utils::ignore_return_value(j.dump()), "[json.exception.type_error.316] invalid UTF-8 byte at index 2: 0xA9", json::type_error&);
+            CHECK_THROWS_WITH_AS(utils::ignore_return_value(j.dump(1, ' ', false, json::error_handler_t::strict)), "[json.exception.type_error.316] invalid UTF-8 byte at index 2: 0xA9", json::type_error&);
             CHECK(j.dump(-1, ' ', false, json::error_handler_t::ignore) == "\"äü\"");
             CHECK(j.dump(-1, ' ', false, json::error_handler_t::replace) == "\"ä\xEF\xBF\xBDü\"");
             CHECK(j.dump(-1, ' ', true, json::error_handler_t::replace) == "\"\\u00e4\\ufffd\\u00fc\"");
@@ -95,8 +98,9 @@ TEST_CASE("serialization")
         {
             const json j = "123\xC2";
 
-            CHECK_THROWS_WITH_AS(j.dump(), "[json.exception.type_error.316] incomplete UTF-8 string; last byte: 0xC2", json::type_error&);
+            // dump() is nodiscard; the exception is thrown by dump() itself before it would return
-            CHECK_THROWS_AS(j.dump(1, ' ', false, json::error_handler_t::strict), json::type_error&);
+            CHECK_THROWS_WITH_AS(utils::ignore_return_value(j.dump()), "[json.exception.type_error.316] incomplete UTF-8 string; last byte: 0xC2", json::type_error&);
+            CHECK_THROWS_AS(utils::ignore_return_value(j.dump(1, ' ', false, json::error_handler_t::strict)), json::type_error&);
             CHECK(j.dump(-1, ' ', false, json::error_handler_t::ignore) == "\"123\"");
             CHECK(j.dump(-1, ' ', false, json::error_handler_t::replace) == "\"123\xEF\xBF\xBD\"");
             CHECK(j.dump(-1, ' ', true, json::error_handler_t::replace) == "\"123\\ufffd\"");
@@ -106,8 +110,9 @@ TEST_CASE("serialization")
         {
             const json j = "123\xF1\xB0\x34\x35\x36";
 
-            CHECK_THROWS_WITH_AS(j.dump(), "[json.exception.type_error.316] invalid UTF-8 byte at index 5: 0x34", json::type_error&);
+            // dump() is nodiscard; the exception is thrown by dump() itself before it would return
-            CHECK_THROWS_AS(j.dump(1, ' ', false, json::error_handler_t::strict), json::type_error&);
+            CHECK_THROWS_WITH_AS(utils::ignore_return_value(j.dump()), "[json.exception.type_error.316] invalid UTF-8 byte at index 5: 0x34", json::type_error&);
+            CHECK_THROWS_AS(utils::ignore_return_value(j.dump(1, ' ', false, json::error_handler_t::strict)), json::type_error&);
             CHECK(j.dump(-1, ' ', false, json::error_handler_t::ignore) == "\"123456\"");
             CHECK(j.dump(-1, ' ', false, json::error_handler_t::replace) == "\"123\xEF\xBF\xBD\x34\x35\x36\"");
             CHECK(j.dump(-1, ' ', true, json::error_handler_t::replace) == "\"123\\ufffd456\"");

tests/src/unit-ubjson.cpp

@@ -2149,172 +2149,6 @@ TEST_CASE("UBJSON")
     }
 }
 
-TEST_CASE("UBJSON nesting does not consume the call stack")
-{
-    // Containers used to be read by calling back into the value reader once
-    // per element, so the native call stack grew with the nesting depth of the
-    // input. '[' alone opens a container, so a payload of repeated '[' crashed
-    // the process (#5104), as did the optimized forms, which reach the same
-    // path through a type or size annotation. The containers are kept on a
-    // heap stack now.
-    //
-    // Deeply nested values must not be compared, copied or dumped here: those
-    // operations are still recursive and would reintroduce the crash.
-    json _;
-
-    SECTION("containers that end at a marker")
-    {
-        const std::vector<uint8_t> input(500000, '[');
-        CHECK_THROWS_WITH_AS(_ = json::from_ubjson(input), "[json.exception.parse_error.110] parse error at byte 500001: syntax error while parsing UBJSON value: unexpected end of input", json::parse_error&);
-        CHECK(json::from_ubjson(input, true, false).is_discarded());
-    }
-
-    SECTION("containers with a size")
-    {
-        std::vector<uint8_t> input;
-        for (std::size_t i = 0; i < 100000; ++i)
-        {
-            input.push_back('[');
-            input.push_back('#');
-            input.push_back('i');
-            input.push_back(1);
-        }
-        CHECK_THROWS_AS(_ = json::from_ubjson(input), json::parse_error&);
-        CHECK(json::from_ubjson(input, true, false).is_discarded());
-    }
-
-    SECTION("containers with a type and a size")
-    {
-        // '[' is a permitted optimized type in UBJSON, so each element of such
-        // a container is itself a container, read without a marker of its own
-        std::vector<uint8_t> input;
-        for (std::size_t i = 0; i < 100000; ++i)
-        {
-            const std::vector<uint8_t> level = {'[', '$', '[', '#', 'i', 1};
-            input.insert(input.end(), level.begin(), level.end());
-        }
-        CHECK_THROWS_AS(_ = json::from_ubjson(input), json::parse_error&);
-        CHECK(json::from_ubjson(input, true, false).is_discarded());
-    }
-
-    SECTION("a well-formed deep value is read through the SAX interface")
-    {
-        std::vector<uint8_t> input(100000, '[');
-        input.insert(input.end(), 100000, ']');
-
-        SaxCountdown accept_all(1000000);
-        CHECK(json::sax_parse(input, &accept_all, json::input_format_t::ubjson));
-    }
-
-    SECTION("a well-formed deep value is read into a value")
-    {
-        const std::size_t depth = 10000;
-        std::vector<uint8_t> input(depth, '[');
-        input.insert(input.end(), depth, ']');
-
-        json j = json::from_ubjson(input);
-
-        std::size_t measured = 0;
-        const json* p = &j;
-        while (p->is_array() && !p->empty())
-        {
-            p = &p->front();
-            ++measured;
-        }
-        // the innermost array is empty, so the descent stops one level short
-        CHECK(measured == depth - 1);
-    }
-
-    SECTION("containers are still read the same way")
-    {
-        CHECK(json::from_ubjson(std::vector<uint8_t>({'[', ']'})) == json::array());
-        CHECK(json::from_ubjson(std::vector<uint8_t>({'{', '}'})) == json::object());
-        CHECK(json::from_ubjson(std::vector<uint8_t>({'[', '#', 'i', 0})) == json::array());
-        CHECK(json::from_ubjson(std::vector<uint8_t>({'{', '#', 'i', 0})) == json::object());
-        CHECK(json::from_ubjson(std::vector<uint8_t>({'[', '$', 'i', '#', 'i', 2, 1, 2})) == json({1, 2}));
-        CHECK(json::from_ubjson(std::vector<uint8_t>({'[', '#', 'i', 2, 'i', 1, 'i', 2})) == json({1, 2}));
-        CHECK(json::from_ubjson(std::vector<uint8_t>({'{', '$', 'i', '#', 'i', 1, 'i', 1, 'a', 1})) == json({{"a", 1}}));
-        // a no-op is not a value, so a container of them holds none
-        CHECK(json::from_ubjson(std::vector<uint8_t>({'[', '$', 'N', '#', 'i', 2})) == json::array());
-        // sized and unsized forms nested inside one another
-        CHECK(json::from_ubjson(std::vector<uint8_t>({'[', '[', '#', 'i', 2, 'i', 1, 'i', 2, ']'})) == json({{1, 2}}));
-        CHECK(json::from_ubjson(std::vector<uint8_t>({'[', '#', 'i', 1, '[', 'i', 1, ']'})) == json({{1}}));
-        // an optimized container of containers
-        CHECK(json::from_ubjson(std::vector<uint8_t>({'[', '$', '[', '#', 'i', 2, 'i', 1, ']', 'i', 2, ']'})) == json({{1}, {2}}));
-    }
-
-    SECTION("BJData containers are still read the same way")
-    {
-        // the ND-array wrapper and the binary shortcut are complete values,
-        // not containers the reader descends into
-        CHECK(json::from_bjdata(std::vector<uint8_t>({'[', '$', 'U', '#', '[', '$', 'i', '#', 'i', 2, 2, 3, 1, 2, 3, 4, 5, 6})) ==
-        json({{"_ArrayType_", "uint8"}, {"_ArraySize_", {2, 3}}, {"_ArrayData_", {1, 2, 3, 4, 5, 6}}}));
-        CHECK(json::from_bjdata(std::vector<uint8_t>({'[', '$', 'i', '#', 'i', 2, 1, 2})) == json({1, 2}));
-        CHECK(json::from_bjdata(std::vector<uint8_t>({'[', '[', 'i', 1, ']', ']'})) == json({{1}}));
-    }
-}
-
-TEST_CASE("UBJSON optimized arrays of a valueless type are bounded")
-{
-    // An element of type 'Z', 'T' or 'F' is encoded by its marker alone, so an
-    // optimized array of one of those has no payload and the declared count is
-    // the only thing deciding how much is allocated. Ten bytes used to produce
-    // billions of values (#2793); every other type costs at least one byte per
-    // element and is bounded by the end of the input.
-    json _;
-
-    SECTION("an excessive count is rejected")
-    {
-        // 'l' is a big-endian int32: 0x7FFFFFFF elements, about 34 GB of value
-        for (const auto marker :
-                {'Z', 'T', 'F'
-                })
-        {
-            const std::vector<uint8_t> input = {'[', '$', static_cast<uint8_t>(marker), '#', 'l', 0x7F, 0xFF, 0xFF, 0xFF};
-            CHECK_THROWS_WITH_AS(_ = json::from_ubjson(input), "[json.exception.out_of_range.408] syntax error while parsing UBJSON size: excessive array size", json::out_of_range&);
-            CHECK(json::from_ubjson(input, true, false).is_discarded());
-        }
-    }
-
-    SECTION("ordinary counts are unaffected")
-    {
-        CHECK(json::from_ubjson(std::vector<uint8_t>({'[', '$', 'Z', '#', 'i', 3})) == json({nullptr, nullptr, nullptr}));
-        CHECK(json::from_ubjson(std::vector<uint8_t>({'[', '$', 'T', '#', 'i', 2})) == json({true, true}));
-        CHECK(json::from_ubjson(std::vector<uint8_t>({'[', '$', 'F', '#', 'i', 2})) == json({false, false}));
-        // 'N' is a no-op rather than a value, and still yields an empty array
-        CHECK(json::from_ubjson(std::vector<uint8_t>({'[', '$', 'N', '#', 'i', 2})) == json::array());
-    }
-
-    SECTION("a type with a payload is unaffected")
-    {
-        // A count past the limit is not rejected for 'U', which costs a byte
-        // per element and is bounded by the end of the input instead. The
-        // count is kept just past the limit rather than made huge, because a
-        // count that also exceeds the array's max_size() is reported as
-        // out_of_range before the input runs out, and max_size() depends on
-        // the width of std::size_t.
-        const std::vector<uint8_t> input = {'[', '$', 'U', '#', 'l', 0x00, 0x10, 0x00, 0x01};
-        CHECK_THROWS_WITH_AS(_ = json::from_ubjson(input), "[json.exception.parse_error.110] parse error at byte 10: syntax error while parsing UBJSON number: unexpected end of input", json::parse_error&);
-        CHECK(json::from_ubjson(input, true, false).is_discarded());
-    }
-
-    SECTION("the writer stays within what the reader accepts")
-    {
-        // below the limit the optimized form is used and is tiny; above it the
-        // writer falls back so that the result can still be read back
-        json const at_limit(1048576, nullptr);
-        const auto v_at_limit = json::to_ubjson(at_limit, true, true);
-        CHECK(v_at_limit.size() == 9);
-        CHECK(v_at_limit.at(1) == '$');
-        CHECK(json::from_ubjson(v_at_limit) == at_limit);
-
-        json const above_limit(1048577, nullptr);
-        const auto v_above_limit = json::to_ubjson(above_limit, true, true);
-        CHECK(v_above_limit.at(1) != '$');
-        CHECK(json::from_ubjson(v_above_limit) == above_limit);
-    }
-}
-
 TEST_CASE("Universal Binary JSON Specification Examples 1")
 {
     SECTION("Null Value")

tests/src/unit-unicode1.cpp

@@ -17,6 +17,7 @@ using nlohmann::json;
 #include <sstream>
 #include <iomanip>
 #include "make_test_data_available.hpp"
+#include "test_utils.hpp"
 
 TEST_CASE("Unicode (1/5)" * doctest::skip())
 {
@@ -240,7 +241,8 @@ void roundtrip(bool success_expected, const std::string& s)
     if (success_expected)
     {
         // serialization succeeds
-        CHECK_NOTHROW(j.dump());
+        // dump() is nodiscard; this only checks that dumping does not throw
+        CHECK_NOTHROW(utils::ignore_return_value(j.dump()));
 
         // exclude parse test for U+0000
         if (s[0] != '\0')
@@ -259,7 +261,8 @@ void roundtrip(bool success_expected, const std::string& s)
     else
     {
         // serialization fails
-        CHECK_THROWS_AS(j.dump(), json::type_error&);
+        // dump() is nodiscard; the exception is thrown by dump() itself before it would return
+        CHECK_THROWS_AS(utils::ignore_return_value(j.dump()), json::type_error&);
 
         // parsing JSON text fails
         CHECK_THROWS_AS(_ = json::parse(ps), json::parse_error&);

tests/src/unit-unicode2.cpp

@@ -19,6 +19,7 @@ using nlohmann::json;
 #include <iostream>
 #include <iomanip>
 #include "make_test_data_available.hpp"
+#include "test_utils.hpp"
 
 // this test suite uses static variables with non-trivial destructors
 DOCTEST_CLANG_SUPPRESS_WARNING_PUSH
@@ -97,7 +98,8 @@ void check_utf8dump(bool success_expected, int byte1, int byte2 = -1, int byte3
     else
     {
         // strict mode must throw if success is not expected
-        CHECK_THROWS_AS(j.dump(), json::type_error&);
+        // dump() is nodiscard; the exception is thrown by dump() itself before it would return
+        CHECK_THROWS_AS(utils::ignore_return_value(j.dump()), json::type_error&);
         // ignore and replace must create different dumps
         CHECK(s_ignored != s_replaced);
 

tests/src/unit-unicode3.cpp

@@ -19,6 +19,7 @@ using nlohmann::json;
 #include <iostream>
 #include <iomanip>
 #include "make_test_data_available.hpp"
+#include "test_utils.hpp"
 
 // this test suite uses static variables with non-trivial destructors
 DOCTEST_CLANG_SUPPRESS_WARNING_PUSH
@@ -97,7 +98,8 @@ void check_utf8dump(bool success_expected, int byte1, int byte2 = -1, int byte3
     else
     {
         // strict mode must throw if success is not expected
-        CHECK_THROWS_AS(j.dump(), json::type_error&);
+        // dump() is nodiscard; the exception is thrown by dump() itself before it would return
+        CHECK_THROWS_AS(utils::ignore_return_value(j.dump()), json::type_error&);
         // ignore and replace must create different dumps
         CHECK(s_ignored != s_replaced);
 

tests/src/unit-unicode4.cpp

@@ -19,6 +19,7 @@ using nlohmann::json;
 #include <iostream>
 #include <iomanip>
 #include "make_test_data_available.hpp"
+#include "test_utils.hpp"
 
 // this test suite uses static variables with non-trivial destructors
 DOCTEST_CLANG_SUPPRESS_WARNING_PUSH
@@ -97,7 +98,8 @@ void check_utf8dump(bool success_expected, int byte1, int byte2 = -1, int byte3
     else
     {
         // strict mode must throw if success is not expected
-        CHECK_THROWS_AS(j.dump(), json::type_error&);
+        // dump() is nodiscard; the exception is thrown by dump() itself before it would return
+        CHECK_THROWS_AS(utils::ignore_return_value(j.dump()), json::type_error&);
         // ignore and replace must create different dumps
         CHECK(s_ignored != s_replaced);
 

tests/src/unit-unicode5.cpp

@@ -19,6 +19,7 @@ using nlohmann::json;
 #include <iostream>
 #include <iomanip>
 #include "make_test_data_available.hpp"
+#include "test_utils.hpp"
 
 // this test suite uses static variables with non-trivial destructors
 DOCTEST_CLANG_SUPPRESS_WARNING_PUSH
@@ -97,7 +98,8 @@ void check_utf8dump(bool success_expected, int byte1, int byte2 = -1, int byte3
     else
     {
         // strict mode must throw if success is not expected
-        CHECK_THROWS_AS(j.dump(), json::type_error&);
+        // dump() is nodiscard; the exception is thrown by dump() itself before it would return
+        CHECK_THROWS_AS(utils::ignore_return_value(j.dump()), json::type_error&);
         // ignore and replace must create different dumps
         CHECK(s_ignored != s_replaced);