Add regression test

README.md

@@ -1649,7 +1649,7 @@ Here is a related issue [#1924](https://github.com/nlohmann/json/issues/1924).
 - The code contains numerous debug **assertions** which can be switched off by defining the preprocessor macro `NDEBUG`, see the [documentation of `assert`](https://en.cppreference.com/w/cpp/error/assert). In particular, note [`operator[]`](https://nlohmann.github.io/json/api/basic_json/operator%5B%5D/) implements **unchecked access** for const objects: If the given key is not present, the behavior is undefined (think of a dereferenced null pointer) and yields an [assertion failure](https://github.com/nlohmann/json/issues/289) if assertions are switched on. If you are not sure whether an element in an object exists, use checked access with the [`at()` function](https://nlohmann.github.io/json/api/basic_json/at/). Furthermore, you can define `JSON_ASSERT(x)` to replace calls to `assert(x)`.
 - As the exact type of a number is not defined in the [JSON specification](https://tools.ietf.org/html/rfc8259.html), this library tries to choose the best fitting C++ number type automatically. As a result, the type `double` may be used to store numbers which may yield [**floating-point exceptions**](https://github.com/nlohmann/json/issues/181) in certain rare situations if floating-point exceptions have been unmasked in the calling code. These exceptions are not caused by the library and need to be fixed in the calling code, such as by re-masking the exceptions prior to calling library functions.
 - The code can be compiled without C++ **runtime type identification** features; that is, you can use the `-fno-rtti` compiler flag.
-- **Exceptions** are used widely within the library. They can, however, be switched off with either using the compiler flag `-fno-exceptions` or by defining the symbol `JSON_NOEXCEPTION`. In this case, exceptions are replaced by `abort()` calls. You can further control this behavior by defining `JSON_THROW_USER` (overriding `throw`), `JSON_TRY_USER` (overriding `try`), and `JSON_CATCH_USER` (overriding `catch`). Note that `JSON_THROW_USER` should leave the current scope (e.g., by throwing or aborting), as continuing after it may yield undefined behavior.
+- **Exceptions** are used widely within the library. They can, however, be switched off with either using the compiler flag `-fno-exceptions` or by defining the symbol `JSON_NOEXCEPTION`. In this case, exceptions are replaced by `abort()` calls. You can further control this behavior by defining `JSON_THROW_USER` (overriding `throw`), `JSON_TRY_USER` (overriding `try`), and `JSON_CATCH_USER` (overriding `catch`). Note that `JSON_THROW_USER` should leave the current scope (e.g., by throwing or aborting), as continuing after it may yield undefined behavior. Note the explanatory [`what()`](https://en.cppreference.com/w/cpp/error/exception/what) string of exceptions is not available for MSVC if exceptions are disabled, see [#2824](https://github.com/nlohmann/json/discussions/2824).
 
 ## Execute unit tests
 

doc/mkdocs/docs/features/macros.md

@@ -32,6 +32,8 @@ When defining `JSON_NOEXCEPTION`, `#!cpp try` is replaced by `#!cpp if (true)`,
 
 The same effect is achieved by setting the compiler flag `-fno-exceptions`.
 
+Note the explanatory [`what()`](https://en.cppreference.com/w/cpp/error/exception/what) string of exceptions is not available for MSVC if exceptions are disabled, see [#2824](https://github.com/nlohmann/json/discussions/2824).
+
 ## `JSON_NO_IO`
 
 When defined, headers `<cstdio>`, `<ios>`, `<iosfwd>`, `<istream>`, and `<ostream>` are not included and parse functions relying on these headers are excluded. This is relevant for environment where these I/O functions are disallowed for security reasons (e.g., Intel Software Guard Extensions (SGX)).

doc/mkdocs/docs/home/exceptions.md

@@ -50,6 +50,8 @@ Note that `JSON_THROW_USER` should leave the current scope (e.g., by throwing or
     #include <nlohmann/json.hpp>
     ```
 
+Note the explanatory [`what()`](https://en.cppreference.com/w/cpp/error/exception/what) string of exceptions is not available for MSVC if exceptions are disabled, see [#2824](https://github.com/nlohmann/json/discussions/2824).
+
 ### Extended diagnostic messages
 
 Exceptions in the library are thrown in the local context of the JSON value they are detected. This makes detailed diagnostics messages, and hence debugging, difficult.

include/nlohmann/detail/output/binary_writer.hpp

@@ -908,6 +908,7 @@ class binary_writer
         if (JSON_HEDLEY_UNLIKELY(it != BasicJsonType::string_t::npos))
         {
             JSON_THROW(out_of_range::create(409, "BSON key cannot contain code point U+0000 (at byte " + std::to_string(it) + ")", j));
+            static_cast<void>(j);
         }
 
         return /*id*/ 1ul + name.size() + /*zero-terminator*/1u;

single_include/nlohmann/json.hpp

@@ -14209,6 +14209,7 @@ class binary_writer
         if (JSON_HEDLEY_UNLIKELY(it != BasicJsonType::string_t::npos))
         {
             JSON_THROW(out_of_range::create(409, "BSON key cannot contain code point U+0000 (at byte " + std::to_string(it) + ")", j));
+            static_cast<void>(j);
         }
 
         return /*id*/ 1ul + name.size() + /*zero-terminator*/1u;

test/CMakeLists.txt

@@ -90,6 +90,16 @@ foreach(file ${files})
     endif()
 endforeach()
 
+# disable exceptions for test-disabled_exceptions
+target_compile_definitions(test-disabled_exceptions PUBLIC JSON_NOEXCEPTION)
+if (CMAKE_CXX_COMPILER_ID STREQUAL "Clang" OR CMAKE_CXX_COMPILER_ID STREQUAL "AppleClang" OR CMAKE_CXX_COMPILER_ID STREQUAL "GNU")
+    target_compile_options(test-disabled_exceptions PUBLIC -fno-exceptions)
+elseif (CMAKE_CXX_COMPILER_ID STREQUAL "MSVC")
+    # disabled due to https://github.com/nlohmann/json/discussions/2824
+    #target_compile_options(test-disabled_exceptions PUBLIC /EH)
+    #target_compile_definitions(test-disabled_exceptions PUBLIC _HAS_EXCEPTIONS=0)
+endif()
+
 add_executable(json_unit EXCLUDE_FROM_ALL $<TARGET_OBJECTS:doctest_main> ${files})
 target_compile_definitions(json_unit PRIVATE DOCTEST_CONFIG_SUPER_FAST_ASSERTS)
 target_compile_options(json_unit PRIVATE

test/src/unit-disabled_exceptions.cpp

@@ -0,0 +1,66 @@
+/*
+    __ _____ _____ _____
+ __|  |   __|     |   | |  JSON for Modern C++ (test suite)
+|  |  |__   |  |  | | | |  version 3.9.1
+|_____|_____|_____|_|___|  https://github.com/nlohmann/json
+
+Licensed under the MIT License <http://opensource.org/licenses/MIT>.
+SPDX-License-Identifier: MIT
+Copyright (c) 2013-2019 Niels Lohmann <http://nlohmann.me>.
+
+Permission is hereby  granted, free of charge, to any  person obtaining a copy
+of this software and associated  documentation files (the "Software"), to deal
+in the Software  without restriction, including without  limitation the rights
+to  use, copy,  modify, merge,  publish, distribute,  sublicense, and/or  sell
+copies  of  the Software,  and  to  permit persons  to  whom  the Software  is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE  IS PROVIDED "AS  IS", WITHOUT WARRANTY  OF ANY KIND,  EXPRESS OR
+IMPLIED,  INCLUDING BUT  NOT  LIMITED TO  THE  WARRANTIES OF  MERCHANTABILITY,
+FITNESS FOR  A PARTICULAR PURPOSE AND  NONINFRINGEMENT. IN NO EVENT  SHALL THE
+AUTHORS  OR COPYRIGHT  HOLDERS  BE  LIABLE FOR  ANY  CLAIM,  DAMAGES OR  OTHER
+LIABILITY, WHETHER IN AN ACTION OF  CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE  OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.
+*/
+
+#include "doctest_compatibility.h"
+
+#include <nlohmann/json.hpp>
+using json = nlohmann::json;
+
+/////////////////////////////////////////////////////////////////////
+// for #2824
+/////////////////////////////////////////////////////////////////////
+
+class sax_no_exception : public nlohmann::detail::json_sax_dom_parser<json>
+{
+  public:
+    explicit sax_no_exception(json& j) : nlohmann::detail::json_sax_dom_parser<json>(j, false) {}
+
+    static bool parse_error(std::size_t /*position*/, const std::string& /*last_token*/, const json::exception& ex)
+    {
+        error_string = new std::string(ex.what()); // NOLINT(cppcoreguidelines-owning-memory)
+        return false;
+    }
+
+    static std::string* error_string;
+};
+
+std::string* sax_no_exception::error_string = nullptr;
+
+TEST_CASE("Tests with disabled exceptions")
+{
+    SECTION("issue #2824 - encoding of json::exception::what()")
+    {
+        json j;
+        sax_no_exception sax(j);
+
+        CHECK (!json::sax_parse("xyz", &sax));
+        CHECK(*sax_no_exception::error_string == "[json.exception.parse_error.101] parse error at line 1, column 1: syntax error while parsing value - invalid literal; last read: 'x'");
+        delete sax_no_exception::error_string; // NOLINT(cppcoreguidelines-owning-memory)
+    }
+}

test/src/unit-regression2.cpp

@@ -156,6 +156,26 @@ struct adl_serializer<NonDefaultConstructible>
 };
 } // namespace nlohmann
 
+/////////////////////////////////////////////////////////////////////
+// for #2824
+/////////////////////////////////////////////////////////////////////
+
+class sax_no_exception : public nlohmann::detail::json_sax_dom_parser<json>
+{
+  public:
+    explicit sax_no_exception(json& j) : nlohmann::detail::json_sax_dom_parser<json>(j, false) {}
+
+    static bool parse_error(std::size_t /*position*/, const std::string& /*last_token*/, const json::exception& ex)
+    {
+        error_string = new std::string(ex.what()); // NOLINT(cppcoreguidelines-owning-memory)
+        return false;
+    }
+
+    static std::string* error_string;
+};
+
+std::string* sax_no_exception::error_string = nullptr;
+
 
 TEST_CASE("regression tests 2")
 {
@@ -621,6 +641,16 @@ TEST_CASE("regression tests 2")
         }
     }
 
+    SECTION("issue #2824 - encoding of json::exception::what()")
+    {
+        json j;
+        sax_no_exception sax(j);
+
+        CHECK (!json::sax_parse("xyz", &sax));
+        CHECK(*sax_no_exception::error_string == "[json.exception.parse_error.101] parse error at line 1, column 1: syntax error while parsing value - invalid literal; last read: 'x'");
+        delete sax_no_exception::error_string; // NOLINT(cppcoreguidelines-owning-memory)
+    }
+
     SECTION("issue #2825 - Properly constrain the basic_json conversion operator")
     {
         static_assert(std::is_copy_assignable<nlohmann::ordered_json>::value, "");