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Allow disabling std::filesystem support

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This can be useful when the compiler claims C++17 support, but standard
library std::filesystem implementation is unavailable (MinGW) or can't
be used because the current macOS target is too low to allow it (#3156).

See #3090.
This commit is contained in:
Vadim Zeitlin 2021-12-14 19:02:17 +01:00
parent 760304635d
commit 5c5fcd01c9
6 changed files with 31 additions and 11 deletions
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4
doc/mkdocs/docs/features/macros.md
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@ -38,6 +38,10 @@ Note the explanatory [`what()`](https://en.cppreference.com/w/cpp/error/exceptio
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)).
## `JSON_NO_STD_FILESYSTEM`
When defined, `<filesystem>` header is not included, even for C++17 compilers, and `std::filesystem::path` support is not available. This can be useful to disable automatically-detected `std::filesystem` support if its implementation in the standard library is suboptimal or even missing.
## `JSON_SKIP_UNSUPPORTED_COMPILER_CHECK`
When defined, the library will not create a compile error when a known unsupported compiler is detected. This allows to use the library with compilers that do not fully support C++11 and may only work if unsupported features are not used.

4
include/nlohmann/detail/conversions/from_json.hpp
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@ -19,7 +19,7 @@
#include <nlohmann/detail/meta/type_traits.hpp>
#include <nlohmann/detail/value_t.hpp>
#ifdef JSON_HAS_CPP_17
#ifdef JSON_HAS_STD_FILESYSTEM
#include <filesystem>
#endif
@ -448,7 +448,7 @@ void from_json(const BasicJsonType& j, std::unordered_map<Key, Value, Hash, KeyE
}
}
#ifdef JSON_HAS_CPP_17
#ifdef JSON_HAS_STD_FILESYSTEM
template<typename BasicJsonType>
void from_json(const BasicJsonType& j, std::filesystem::path& p)
{

4
include/nlohmann/detail/conversions/to_json.hpp
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@ -15,7 +15,7 @@
#include <nlohmann/detail/meta/type_traits.hpp>
#include <nlohmann/detail/value_t.hpp>
#ifdef JSON_HAS_CPP_17
#ifdef JSON_HAS_STD_FILESYSTEM
#include <filesystem>
#endif
@ -391,7 +391,7 @@ void to_json(BasicJsonType& j, const T& t)
to_json_tuple_impl(j, t, make_index_sequence<std::tuple_size<T>::value> {});
}
#ifdef JSON_HAS_CPP_17
#ifdef JSON_HAS_STD_FILESYSTEM
template<typename BasicJsonType>
void to_json(BasicJsonType& j, const std::filesystem::path& p)
{

7
include/nlohmann/detail/macro_scope.hpp
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@ -37,6 +37,13 @@
#define JSON_HAS_CPP_11
#endif
// Optimistically assume that all compilers providing C++17 support also
// provide std::filesystem in their standard library. Realistically allow
// overriding this because this is not the case in practice.
#if defined(JSON_HAS_CPP_17) && !defined(JSON_NO_STD_FILESYSTEM)
#define JSON_HAS_STD_FILESYSTEM
#endif
// disable documentation warnings on clang
#if defined(__clang__)
#pragma clang diagnostic push

17
single_include/nlohmann/json.hpp
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@ -2325,6 +2325,13 @@ using is_detected_convertible =
#define JSON_HAS_CPP_11
#endif
// Optimistically assume that all compilers providing C++17 support also
// provide std::filesystem in their standard library. Realistically allow
// overriding this because this is not the case in practice.
#if defined(JSON_HAS_CPP_17) && !defined(JSON_NO_STD_FILESYSTEM)
#define JSON_HAS_STD_FILESYSTEM
#endif
// disable documentation warnings on clang
#if defined(__clang__)
#pragma clang diagnostic push
@ -3950,7 +3957,7 @@ T conditional_static_cast(U value)
// #include <nlohmann/detail/value_t.hpp>
#ifdef JSON_HAS_CPP_17
#ifdef JSON_HAS_STD_FILESYSTEM
#include <filesystem>
#endif
@ -4379,7 +4386,7 @@ void from_json(const BasicJsonType& j, std::unordered_map<Key, Value, Hash, KeyE
}
}
#ifdef JSON_HAS_CPP_17
#ifdef JSON_HAS_STD_FILESYSTEM
template<typename BasicJsonType>
void from_json(const BasicJsonType& j, std::filesystem::path& p)
{
@ -4626,7 +4633,7 @@ class tuple_element<N, ::nlohmann::detail::iteration_proxy_value<IteratorType >>
// #include <nlohmann/detail/value_t.hpp>
#ifdef JSON_HAS_CPP_17
#ifdef JSON_HAS_STD_FILESYSTEM
#include <filesystem>
#endif
@ -5002,7 +5009,7 @@ void to_json(BasicJsonType& j, const T& t)
to_json_tuple_impl(j, t, make_index_sequence<std::tuple_size<T>::value> {});
}
#ifdef JSON_HAS_CPP_17
#ifdef JSON_HAS_STD_FILESYSTEM
template<typename BasicJsonType>
void to_json(BasicJsonType& j, const std::filesystem::path& p)
{
@ -17747,7 +17754,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
detail::parser_callback_t<basic_json>cb = nullptr,
const bool allow_exceptions = true,
const bool ignore_comments = false
)
)
{
return ::nlohmann::detail::parser<basic_json, InputAdapterType>(std::move(adapter),
std::move(cb), allow_exceptions, ignore_comments);

6
test/src/unit-regression2.cpp
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@ -46,8 +46,10 @@ using ordered_json = nlohmann::ordered_json;
#define JSON_HAS_CPP_17
#endif
#ifdef JSON_HAS_CPP_17
#ifdef JSON_HAS_STD_FILESYSTEM
#include <filesystem>
#endif
#ifdef JSON_HAS_CPP_17
#include <variant>
#endif
@ -728,7 +730,7 @@ TEST_CASE("regression tests 2")
CHECK(j == k);
}
#ifdef JSON_HAS_CPP_17
#ifdef JSON_HAS_STD_FILESYSTEM
SECTION("issue #3070 - Version 3.10.3 breaks backward-compatibility with 3.10.2 ")
{
std::filesystem::path text_path("/tmp/text.txt");