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Fix constraints on from_json() for strings (fixes #3171, #3267, #3312, #3384) #3427

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Apr 8, 2022
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Fix constraints on from_json() for strings (fixes #3171, #3267, #3312, #3384) #3427

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11 changes: 5 additions & 6 deletions include/nlohmann/detail/conversions/from_json.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -105,13 +105,12 @@ void from_json(const BasicJsonType& j, typename BasicJsonType::string_t& s)
}

template <
typename BasicJsonType, typename ConstructibleStringType,
typename BasicJsonType, typename StringType,
enable_if_t <
is_constructible_string_type<BasicJsonType, ConstructibleStringType>::value&&
!std::is_same<typename BasicJsonType::string_t,
ConstructibleStringType>::value,
int > = 0 >
void from_json(const BasicJsonType& j, ConstructibleStringType& s)
std::is_assignable<StringType&, const typename BasicJsonType::string_t>::value
&& !std::is_same<typename BasicJsonType::string_t, StringType>::value
&& !is_json_ref<StringType>::value, int > = 0 >
void from_json(const BasicJsonType& j, StringType& s)
{
if (JSON_HEDLEY_UNLIKELY(!j.is_string()))
{
Expand Down
11 changes: 5 additions & 6 deletions single_include/nlohmann/json.hpp
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Expand Up @@ -3928,13 +3928,12 @@ void from_json(const BasicJsonType& j, typename BasicJsonType::string_t& s)
}

template <
typename BasicJsonType, typename ConstructibleStringType,
typename BasicJsonType, typename StringType,
enable_if_t <
is_constructible_string_type<BasicJsonType, ConstructibleStringType>::value&&
!std::is_same<typename BasicJsonType::string_t,
ConstructibleStringType>::value,
int > = 0 >
void from_json(const BasicJsonType& j, ConstructibleStringType& s)
std::is_assignable<StringType&, const typename BasicJsonType::string_t>::value
&& !std::is_same<typename BasicJsonType::string_t, StringType>::value
&& !is_json_ref<StringType>::value, int > = 0 >
void from_json(const BasicJsonType& j, StringType& s)
{
if (JSON_HEDLEY_UNLIKELY(!j.is_string()))
{
Expand Down
5 changes: 0 additions & 5 deletions test/CMakeLists.txt
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Expand Up @@ -11,11 +11,6 @@ include(test)
# override standard support
#############################################################################

# compiling json.hpp in C++14 mode fails with Clang <4.0
if (CMAKE_CXX_COMPILER_ID STREQUAL "Clang" AND CMAKE_CXX_COMPILER_VERSION VERSION_LESS 4.0)
unset(compiler_supports_cpp_14)
endif()

# Clang only supports C++17 starting from Clang 5.0
if (CMAKE_CXX_COMPILER_ID STREQUAL "Clang" AND CMAKE_CXX_COMPILER_VERSION VERSION_LESS 5.0)
unset(compiler_supports_cpp_17)
Expand Down
69 changes: 69 additions & 0 deletions test/src/unit-regression2.cpp
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Expand Up @@ -240,6 +240,50 @@ inline void from_json(const nlohmann::json& j, FooBar& fb)
j.at("value").get_to(fb.foo.value);
}

/////////////////////////////////////////////////////////////////////
// for #3171
/////////////////////////////////////////////////////////////////////

struct for_3171_base // NOLINT(cppcoreguidelines-special-member-functions)
{
for_3171_base(const std::string& /*unused*/ = {}) {}
virtual ~for_3171_base() = default;

virtual void _from_json(const json& j)
{
j.at("str").get_to(str);
}

std::string str{};
};

struct for_3171_derived : public for_3171_base
{
for_3171_derived() = default;
explicit for_3171_derived(const std::string& /*unused*/) { }
};

inline void from_json(const json& j, for_3171_base& tb)
{
tb._from_json(j);
}

/////////////////////////////////////////////////////////////////////
// for #3312
/////////////////////////////////////////////////////////////////////

#ifdef JSON_HAS_CPP_20
struct for_3312
{
std::string name;
};

inline void from_json(const json& j, for_3312& obj)
{
j.at("name").get_to(obj.name);
}
#endif

TEST_CASE("regression tests 2")
{
SECTION("issue #1001 - Fix memory leak during parser callback")
Expand Down Expand Up @@ -791,6 +835,31 @@ TEST_CASE("regression tests 2")
CHECK(jit->first == ojit->first);
CHECK(jit->second.get<std::string>() == ojit->second.get<std::string>());
}

SECTION("issue #3171 - if class is_constructible from std::string wrong from_json overload is being selected, compilation failed")
{
json j{{ "str", "value"}};

// failed with: error: no match for ‘operator=’ (operand types are ‘for_3171_derived’ and ‘const nlohmann::basic_json<>::string_t’
// {aka ‘const std::__cxx11::basic_string<char>’})
// s = *j.template get_ptr<const typename BasicJsonType::string_t*>();
auto td = j.get<for_3171_derived>();

CHECK(td.str == "value");
}

#ifdef JSON_HAS_CPP_20
SECTION("issue #3312 - Parse to custom class from unordered_json breaks on G++11.2.0 with C++20")
{
// see test for #3171
ordered_json j = {{"name", "class"}};
for_3312 obj{};

j.get_to(obj);

CHECK(obj.name == "class");
}
#endif
}

DOCTEST_CLANG_SUPPRESS_WARNING_POP