Standard Library Modules: `uniform_real_distribution` emits error C2512: `'std::_Unsigned128'`: no appropriate default constructor available

[larioteo]

Describe the bug

It seems there was a bug introduced with the latest preview version, std::uniform_real_distribution doesn't work as expected under C++ Latest with experimental modules enabled.

Simple Example

import std;

int main() {
    std::mt19937 engine{ std::random_device{}() };
    std::uniform_real_distribution<double> dist(0.0, 1.0);
    double result = dist(engine);
    return 0;
}

Expected behavior

The code should compile and run without errors as it did in previous versions

STL version

Microsoft Visual Studio Community 2022 (64-bit) - Preview
Version 17.12.0 Preview 1.0

Additional context

Worked on 17.11.0 Preview 6.0

Compiler Log

Build started at 20:40...
1>------ Build started: Project: Random, Configuration: Debug x64 ------
1>Scanning sources for module dependencies...
1>std.ixx
1>std.compat.ixx
1>Compiling...
1>std.ixx
1>std.compat.ixx
1>Random.cpp
1>C:\Program Files\Microsoft Visual Studio\2022\Preview\VC\Tools\MSVC\14.42.34226\include\__msvc_int128.hpp(826,22): error C2512: 'std::_Unsigned128': no appropriate default constructor available
1>(compiling source file 'Random.cpp')
1>    C:\Program Files\Microsoft Visual Studio\2022\Preview\VC\Tools\MSVC\14.42.34226\include\random(273,48):
1>    while evaluating constexpr function 'std::operator +'
1>    C:\Program Files\Microsoft Visual Studio\2022\Preview\VC\Tools\MSVC\14.42.34226\include\random(311,34):
1>    while evaluating constexpr function 'std::_Generate_canonical_params'
1>    C:\Program Files\Microsoft Visual Studio\2022\Preview\VC\Tools\MSVC\14.42.34226\include\__msvc_int128.hpp(826,22):
1>    the template instantiation context (the oldest one first) is
1>        D:\Research\RandomBug\Random\Random.cpp(6,21):
1>        see reference to function template instantiation 'double std::uniform_real_distribution<double>::operator ()<std::mt19937>(_Engine &)' being compiled
1>        with
1>        [
1>            _Engine=std::mt19937
1>        ]
1>            D:\Research\RandomBug\Random\Random.cpp(6,19):
1>            see the first reference to 'std::uniform_real_distribution<double>::operator ()' in 'main'
1>        C:\Program Files\Microsoft Visual Studio\2022\Preview\VC\Tools\MSVC\14.42.34226\include\random(3287,25):
1>        see reference to function template instantiation 'double std::uniform_real<_Ty>::operator ()<_Engine>(_Engine &)' being compiled
1>        with
1>        [
1>            _Ty=double,
1>            _Engine=std::mt19937
1>        ]
1>        C:\Program Files\Microsoft Visual Studio\2022\Preview\VC\Tools\MSVC\14.42.34226\include\random(3182,16):
1>        see reference to function template instantiation 'double std::uniform_real<_Ty>::_Eval<_Engine>(_Engine &,const std::uniform_real<_Ty>::param_type &) const' being compiled
1>        with
1>        [
1>            _Ty=double,
1>            _Engine=std::mt19937
1>        ]
1>        C:\Program Files\Microsoft Visual Studio\2022\Preview\VC\Tools\MSVC\14.42.34226\include\random(3222,16):
1>        see reference to function template instantiation '_Real std::_Nrand_impl<_Ty,_Engine>(_Gen &)' being compiled
1>        with
1>        [
1>            _Real=double,
1>            _Ty=double,
1>            _Engine=std::mt19937,
1>            _Gen=std::mt19937
1>        ]
1>        C:\Program Files\Microsoft Visual Studio\2022\Preview\VC\Tools\MSVC\14.42.34226\include\random(419,21):
1>        see reference to function template instantiation '_Real std::generate_canonical<_Real,53,_Gen>(_Gen &)' being compiled
1>        with
1>        [
1>            _Real=double,
1>            _Gen=std::mt19937
1>        ]
1>C:\Program Files\Microsoft Visual Studio\2022\Preview\VC\Tools\MSVC\14.42.34226\include\random(311,32): error C2131: expression did not evaluate to a constant
1>(compiling source file 'Random.cpp')
1>    C:\Program Files\Microsoft Visual Studio\2022\Preview\VC\Tools\MSVC\14.42.34226\include\__msvc_int128.hpp(826,22):
1>    a non-constant (sub-)expression was encountered
1>C:\Program Files\Microsoft Visual Studio\2022\Preview\VC\Tools\MSVC\14.42.34226\include\random(314,46): error C2975: '_Test': invalid template argument for 'std::conditional_t', expected compile-time constant expression
1>(compiling source file 'Random.cpp')
1>    C:\Program Files\Microsoft Visual Studio\2022\Preview\VC\Tools\MSVC\14.42.34226\include\xtr1common(68,28):
1>    see declaration of '_Test'
1>C:\Program Files\Microsoft Visual Studio\2022\Preview\VC\Tools\MSVC\14.42.34226\include\random(313,59): error C2975: '_Test': invalid template argument for 'std::conditional_t', expected compile-time constant expression
1>(compiling source file 'Random.cpp')
1>    C:\Program Files\Microsoft Visual Studio\2022\Preview\VC\Tools\MSVC\14.42.34226\include\xtr1common(68,28):
1>    see declaration of '_Test'
1>C:\Program Files\Microsoft Visual Studio\2022\Preview\VC\Tools\MSVC\14.42.34226\include\random(315,18): error C2512: 'std::_Unsigned128': no appropriate default constructor available
1>(compiling source file 'Random.cpp')
1>    C:\Program Files\Microsoft Visual Studio\2022\Preview\VC\Tools\MSVC\14.42.34226\include\__msvc_int128.hpp(706,8):
1>    see declaration of 'std::_Unsigned128'
1>C:\Program Files\Microsoft Visual Studio\2022\Preview\VC\Tools\MSVC\14.42.34226\include\random(317,30): error C2131: expression did not evaluate to a constant
1>(compiling source file 'Random.cpp')
1>    C:\Program Files\Microsoft Visual Studio\2022\Preview\VC\Tools\MSVC\14.42.34226\include\__msvc_int128.hpp(826,22):
1>    a non-constant (sub-)expression was encountered
1>C:\Program Files\Microsoft Visual Studio\2022\Preview\VC\Tools\MSVC\14.42.34226\include\random(319,39): error C2131: expression did not evaluate to a constant
1>(compiling source file 'Random.cpp')
1>    C:\Program Files\Microsoft Visual Studio\2022\Preview\VC\Tools\MSVC\14.42.34226\include\__msvc_int128.hpp(826,22):
1>    a non-constant (sub-)expression was encountered
1>C:\Program Files\Microsoft Visual Studio\2022\Preview\VC\Tools\MSVC\14.42.34226\include\random(321,46): error C2131: expression did not evaluate to a constant
1>(compiling source file 'Random.cpp')
1>    C:\Program Files\Microsoft Visual Studio\2022\Preview\VC\Tools\MSVC\14.42.34226\include\__msvc_int128.hpp(826,22):
1>    a non-constant (sub-)expression was encountered
1>C:\Program Files\Microsoft Visual Studio\2022\Preview\VC\Tools\MSVC\14.42.34226\include\random(322,40): error C2131: expression did not evaluate to a constant
1>(compiling source file 'Random.cpp')
1>    C:\Program Files\Microsoft Visual Studio\2022\Preview\VC\Tools\MSVC\14.42.34226\include\__msvc_int128.hpp(826,22):
1>    a non-constant (sub-)expression was encountered
1>C:\Program Files\Microsoft Visual Studio\2022\Preview\VC\Tools\MSVC\14.42.34226\include\random(336,39): error C2131: expression did not evaluate to a constant
1>(compiling source file 'Random.cpp')
1>    C:\Program Files\Microsoft Visual Studio\2022\Preview\VC\Tools\MSVC\14.42.34226\include\__msvc_int128.hpp(826,22):
1>    a non-constant (sub-)expression was encountered
1>C:\Program Files\Microsoft Visual Studio\2022\Preview\VC\Tools\MSVC\14.42.34226\include\random(337,39): error C2131: expression did not evaluate to a constant
1>(compiling source file 'Random.cpp')
1>    C:\Program Files\Microsoft Visual Studio\2022\Preview\VC\Tools\MSVC\14.42.34226\include\__msvc_int128.hpp(826,22):
1>    a non-constant (sub-)expression was encountered
1>C:\Program Files\Microsoft Visual Studio\2022\Preview\VC\Tools\MSVC\14.42.34226\include\random(342,43): error C2131: expression did not evaluate to a constant
1>(compiling source file 'Random.cpp')
1>    C:\Program Files\Microsoft Visual Studio\2022\Preview\VC\Tools\MSVC\14.42.34226\include\__msvc_int128.hpp(826,22):
1>    a non-constant (sub-)expression was encountered
1>C:\Program Files\Microsoft Visual Studio\2022\Preview\VC\Tools\MSVC\14.42.34226\include\random(344,50): error C2131: expression did not evaluate to a constant
1>(compiling source file 'Random.cpp')
1>    C:\Program Files\Microsoft Visual Studio\2022\Preview\VC\Tools\MSVC\14.42.34226\include\__msvc_int128.hpp(826,22):
1>    a non-constant (sub-)expression was encountered
1>Done building project "Random.vcxproj" -- FAILED.
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========
========== Build completed at 20:40 and took 03,809 seconds ==========

[CaseyCarter]

_Unsigned128 inherits a default constructor from _Base128. This looks like a compiler regression. The workaround we have for pre-C++17-inherited constructors seems to fix this as well:

STL/stl/inc/__msvc_int128.hpp

Lines 710 to 712 in 62205ab

	#if !_HAS_CXX17
	constexpr _Unsigned128() noexcept : _Base128{} {}
	#endif // !_HAS_CXX17

[StephanTLavavej]

Thanks for the report! Can we ask you to report this on VS Developer Community, at https://developercommunity.visualstudio.com/cpp/report ?

The compiler team wants to track all issues there and they'd like customers to directly report issues (instead of MSVC team members). Sorry for asking you to do a bit more paperwork.

[StephanTLavavej]

I'll report it.

By the way, when using import std; or import std.compat;, all you need is /std:c++latest (or /std:c++20).

You don't need the "experimental modules" selected in the VS Installer, and you shouldn't use the /experimental:module compiler option - that was for the older, limited, non-Standard import std.core; et al.

[StephanTLavavej]

DevCom-10729775 "Standard Library Modules: Random number machinery emits bogus error C2512: 'std::_Unsigned128': no appropriate default constructor available".

[larioteo]

Sorry for being late; I simply haven't had time until now :).

Next time, I'll report it through the developer community as well.

Thanks! I overlooked that the /experimental:module option is no longer needed.

[StephanTLavavej]

Awesome, thanks again for being an early adopter of modules! I've merged the library workarounds for VS 2022 17.12 Preview 3. However, I encountered a compiler assertion in our internal "checked" builds (that aren't active in the "retail" builds that we ship publicly). This assertion might be over-eager, but it might also indicate remaining problems that could appear with the retail compiler under more intensive usage. Please let us know if you run into any remaining weirdness.

[peter1745]

This seems to be happening in Visual Studio 17.12 Preview 1.0 and Preview 2.0

[CaseyCarter]

This seems to be happening in Visual Studio 17.12 Preview 1.0 and Preview 2.0

The fix should be in VS 2022 17.12 Preview 3.