Add stdlib version check for C++20 #3754
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include/fmt/core.h
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| #if (FMT_CPLUSPLUS >= 202002L || \ | ||
| (FMT_CPLUSPLUS >= 201709L && FMT_GCC_VERSION >= 1002)) && \ | ||
| ((!defined(_GLIBCXX_RELEASE) || _GLIBCXX_RELEASE >= 10) && \ | ||
| (!defined(_LIBCPP_VERSION) || _LIBCPP_VERSION >= 10000) && \ | ||
| (!FMT_MSC_VERSION || FMT_MSC_VERSION >= 1928)) |
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What is the idea behind this change? Shall we enable FMT_CONSTEXPR20 only if is_constant_evaluated is available instead? Something like
#if defined(FMT_HAS_IS_CONSTANT_EVALUATED) && \
((FMT_CPLUSPLUS >= 202002L) && \
(!defined(_GLIBCXX_RELEASE) || _GLIBCXX_RELEASE > 9)) || \
(FMT_CPLUSPLUS >= 201709L && FMT_GCC_VERSION >= 1002)
# define FMT_CONSTEXPR20 constexprThere was a problem hiding this comment.
Main idea: Enable C++20 constexpr only if stdlib support C++20.
The condition (!defined(_GLIBCXX_RELEASE) || _GLIBCXX_RELEASE > 9) partially check stdlib C++20 features. I extended it for libcxx and MSVC.
FMT_CONSTEXPR20 enabled if compiler support C++20 AND the version of stdlib is modern to support C++20.
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The compiler does not define _LIBCPP_VERSION in Android's case.
This will result in FMT_CONSTEXPR20 being incorrectly set to constexpr.
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Try to find the __config file in the source code of your standard library and look at the value of the _LIBCPP_VERSION macro.
Or in repository, like this:
https://android.googlesource.com/platform/external/libcxx/+/refs/tags/android-cts-10.0_r15/include/__config#36
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👍 I see # define _LIBCPP_VERSION 170000
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@hchataing
Interesting!
libcxx version 170000 fully supports C++20 and you shouldn't have issue #3745.
Can you compile and run the program:
#include <iostream>
int main()
{
std::cerr << _LIBCPP_VERSION << std::endl;
return 0;
}in issue #3745 build environment?
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I think we should just go with enabling C++20 constexpr only if consteval is also available.
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Sorry, I meant is_constant_evaluated because that's what causing the OP's problem.
Signed-off-by: Vladislav Shchapov <vladislav@shchapov.ru>
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Thanks! |
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Sorry I did not have the time to validate the fix 😞 It looks like it should be working. |
Signed-off-by: Vladislav Shchapov <vladislav@shchapov.ru>
Possible fix #3745