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TOML_DISABLE_NOEXCEPT_NOEXCEPT workaround MSVC bug noexcept + modules #271

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Merged
merged 1 commit into from
May 15, 2025
Merged

TOML_DISABLE_NOEXCEPT_NOEXCEPT workaround MSVC bug noexcept + modules #271

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16 changes: 16 additions & 0 deletions include/toml++/impl/preprocessor.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1252,6 +1252,22 @@ TOML_ENABLE_WARNINGS;
/// These compile errors were reported by Kevin Dick, Jan 19, 2024, at https://github.com/marzer/tomlplusplus/issues/219
//# }}

#ifndef TOML_DISABLE_NOEXCEPT_NOEXCEPT
#define TOML_DISABLE_NOEXCEPT_NOEXCEPT 0
#ifdef _MSC_VER
#if _MSC_VER <= 1943 // Up to Visual Studio 2022 Version 17.13.6
#undef TOML_DISABLE_NOEXCEPT_NOEXCEPT
#define TOML_DISABLE_NOEXCEPT_NOEXCEPT 1
#endif
#endif
#endif
//# {{
/// \def TOML_DISABLE_NOEXCEPT_NOEXCEPT
/// \brief Disable using noexcept(noexcept(<expression>)) within the toml++ library implementation.
/// \detail This macro offers a workaround to a bug in Visual C++ (Visual Studio 2022), which caused
/// compile errors, saying: "error C3878: syntax error: unexpected token ',' following 'simple-type-specifier'"
//# }}

/// @}
//#====================================================================================================================
//# CHARCONV SUPPORT
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7 changes: 5 additions & 2 deletions include/toml++/impl/value.hpp
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Expand Up @@ -266,8 +266,11 @@ TOML_NAMESPACE_START
(impl::value_variadic_ctor_allowed<value<ValueType>, impl::remove_cvref<Args>...>::value),
typename... Args)
TOML_NODISCARD_CTOR
explicit value(Args&&... args) noexcept(noexcept(value_type(
impl::native_value_maker<value_type, std::decay_t<Args>...>::make(static_cast<Args&&>(args)...))))
explicit value(Args&&... args)
#if !TOML_DISABLE_NOEXCEPT_NOEXCEPT
noexcept(noexcept(value_type(
impl::native_value_maker<value_type, std::decay_t<Args>...>::make(static_cast<Args&&>(args)...))))
#endif
Comment on lines -269 to +273
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This is the only use of noexcept(noexcept(<expression>)) in toml++, and while a regular MSVC build appears to be able to parse it, it fails when using the tomlplusplus module (doing a C++20 compilation).

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Honestly, MSVC does compile noexcept(noexcept(<expression>)) in other situations. I don't know exactly in which particular situations noexcept(noexcept(<expression>)) triggers an error, but this is one of them 🤷

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Still "Draft" because I haven't yet figured out if this is a known compiler bug. Otherwise, maybe it should be reported!

The added value of this particular noexcept specifier looks rather small, right? 🤷 So then, is it OK to put it inside an #if ... #endif?

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Hmmn, might be able to work around this by extracting the inner noexcept() out into a separate typedef or template variable, then using that in the outer noexcept()?

Otherwise yeah I'm OK with a switch to turn it off.

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My feeling is that the combination of variadic templates + noexcept(noexcept(...)) + modules is more than MSVC can handle. You can use each feature, just don't combine them 😸

: val_(impl::native_value_maker<value_type, std::decay_t<Args>...>::make(static_cast<Args&&>(args)...))
{
#if TOML_LIFETIME_HOOKS
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17 changes: 15 additions & 2 deletions toml.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1137,6 +1137,16 @@ TOML_ENABLE_WARNINGS;
#define TOML_DISABLE_CONDITIONAL_NOEXCEPT_LAMBDA 0
#endif

#ifndef TOML_DISABLE_NOEXCEPT_NOEXCEPT
#define TOML_DISABLE_NOEXCEPT_NOEXCEPT 0
#ifdef _MSC_VER
#if _MSC_VER <= 1943 // Up to Visual Studio 2022 Version 17.13.6
#undef TOML_DISABLE_NOEXCEPT_NOEXCEPT
#define TOML_DISABLE_NOEXCEPT_NOEXCEPT 1
#endif
#endif
#endif

#if !defined(TOML_FLOAT_CHARCONV) && (TOML_GCC || TOML_CLANG || (TOML_ICC && !TOML_ICC_CL))
// not supported by any version of GCC or Clang as of 26/11/2020
// not supported by any version of ICC on Linux as of 11/01/2021
Expand Down Expand Up @@ -5088,8 +5098,11 @@ TOML_NAMESPACE_START
(impl::value_variadic_ctor_allowed<value<ValueType>, impl::remove_cvref<Args>...>::value),
typename... Args)
TOML_NODISCARD_CTOR
explicit value(Args&&... args) noexcept(noexcept(value_type(
impl::native_value_maker<value_type, std::decay_t<Args>...>::make(static_cast<Args&&>(args)...))))
explicit value(Args&&... args)
#if !TOML_DISABLE_NOEXCEPT_NOEXCEPT
noexcept(noexcept(value_type(
impl::native_value_maker<value_type, std::decay_t<Args>...>::make(static_cast<Args&&>(args)...))))
#endif
: val_(impl::native_value_maker<value_type, std::decay_t<Args>...>::make(static_cast<Args&&>(args)...))
{
#if TOML_LIFETIME_HOOKS
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