C++/WinRT, part of Windows SDK 17134 is not compatible with Visual Studio 15.8 Preview 3

Question

Trying to compile the following code:

#include <winrt/base.h>

int main() {}

With the following compiler options:

/permissive- /std:c++latest

With recently released Visual Studio 15.8 Preview 3.0 results in the following compilation errors:

1>------ Build started: Project: test1, Configuration: Debug x64 ------
1>Source.cpp
1>c:\program files (x86)\windows kits\10\include\10.0.17134.0\cppwinrt\winrt\base.h(2185): error C3861: 'from_abi': identifier not found
1>c:\program files (x86)\windows kits\10\include\10.0.17134.0\cppwinrt\winrt\base.h(2185): note: This diagnostic occurred in the compiler generated function 'conditional<_Test,T,_Ty2>::type winrt::impl::as(From *)'
1>        with
1>        [
1>            _Ty2=winrt::com_ptr<T>
1>        ]
1>c:\program files (x86)\windows kits\10\include\10.0.17134.0\cppwinrt\winrt\base.h(2209): error C3861: 'from_abi': identifier not found
1>c:\program files (x86)\windows kits\10\include\10.0.17134.0\cppwinrt\winrt\base.h(2209): note: This diagnostic occurred in the compiler generated function 'conditional<_Test,T,_Ty2>::type winrt::impl::try_as(From *) noexcept'
1>        with
1>        [
1>            _Ty2=winrt::com_ptr<T>
1>        ]
1>c:\program files (x86)\windows kits\10\include\10.0.17134.0\cppwinrt\winrt\base.h(3850): error C3861: 'from_abi': identifier not found
1>c:\program files (x86)\windows kits\10\include\10.0.17134.0\cppwinrt\winrt\base.h(3873): note: see reference to class template instantiation 'winrt::weak_ref<T>' being compiled
1>c:\program files (x86)\windows kits\10\include\10.0.17134.0\cppwinrt\winrt\base.h(2984): note: see reference to class template instantiation 'winrt::com_ptr<ILanguageExceptionErrorInfo2>' being compiled
1>c:\program files (x86)\windows kits\10\include\10.0.17134.0\cppwinrt\winrt\base.h(3054): note: see reference to class template instantiation 'winrt::com_ptr<IRestrictedErrorInfo>' being compiled
1>c:\program files (x86)\microsoft visual studio\preview\professional\vc\tools\msvc\14.15.26608\include\type_traits(616): note: see reference to class template instantiation 'std::basic_string_view<wchar_t,std::char_traits<wchar_t>>' being compiled
1>c:\program files (x86)\microsoft visual studio\preview\professional\vc\tools\msvc\14.15.26608\include\xstring(2124): note: see reference to class template instantiation 'std::is_convertible<const _StringViewIsh &,std::basic_string_view<wchar_t,std::char_traits<wchar_t>>>' being compiled
1>        with
1>        [
1>            _StringViewIsh=const wchar_t *
1>        ]
1>c:\program files (x86)\microsoft visual studio\preview\professional\vc\tools\msvc\14.15.26608\include\xstring(2122): note: see reference to variable template 'const bool conjunction_v<std::is_convertible<wchar_t const * const &,std::basic_string_view<wchar_t,std::char_traits<wchar_t> > >,std::negation<std::is_convertible<wchar_t const * const &,wchar_t const *> > >' being compiled
1>c:\program files (x86)\microsoft visual studio\preview\professional\vc\tools\msvc\14.15.26608\include\xstring(2281): note: see reference to alias template instantiation '_Is_string_view_ish<const wchar_t*>' being compiled
1>c:\program files (x86)\windows kits\10\include\10.0.17134.0\cppwinrt\winrt\base.h(6308): error C3861: 'to_abi': identifier not found
1>Done building project "test1.vcxproj" -- FAILED.
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========

Is there any solution?

Saltant

Do you have a supported version of the Windows SDK (version 10.0.17134.0 (Windows 10, version 1803) or later)? See the documentation for from_abi. – Curlew

I'm able to repro this issue. It appears that 17134 version of C++/WinRT is not compatible with VS 2017 (15.8 update preview 3) even without /permissive-... Might be a compiler issue, so I'll ping the teams involved. – Garnish

Also note that you should be using /std:c++17 and not /std:c++latest with VS 2017. You only need C++17 support for C++/WinRT, not some future C++20. – Garnish

It may be so for C++/WinRT, but it is not the only component in a program. Other parts may require features not available in C++17 – Saltant

This issue also happens with Visual Studio 2017 15.8.0, released on August 14, 2018. The answer implies, that this is an issue that needs to be resolved with an SDK update, so that shouldn't be a surprise. I'm just leaving this information in case a future visitor that isn't using a Visual Studio Preview runs into this issue as well (like myself). – Passade

Currently I work around this issue by installing and using Windows 10 Preview SDK 10.0.17709.0. – Saltant

Answer 1

This is a known issue which will be addressed in a future Windows 10 SDK update.

You can work around it by either turning off Conformance Mode entirely (/permissive-), -or- keep it on by adding to the Additional Options /Zc:twoPhase- to disable two-phase name lookup.

You should use /std:c++17 and not /std:c++latest with VS 2017 for C++/WinRT to enable C++17 without opting in to future draft changes.

UPDATE: This issue is resolved using the Windows 10 October 2018 Update SDK (17763).

Garnish

The combination /permissive- /Zc:twoPhase- /std:c++latest appears to work, in case you need experimental features in your compilation unit. It is unclear to me, why C++/WinRT doesn't, though, as it relies on/makes available coroutines, which aren't part of C++17. What's the deal here, in case you know? – Passade

C++/WinRT headers for C++17 requires inline namespaces, but otherwise only requires C++14 generalized constexpr to build. Use of co-routines is strongly encouraged, but isn't actually part of C++11, C++14, or C++17. It's enabled via the /await flag. – Garnish

/permissive- was already there - /Zc:twoPhase- worked though. – Liter

What exactly is 'breaking' here? – Garnish

@ChuckWalbourn turning off Conformance Mode has a devastating impact, for example operator names will stop working. – Banka

To my knowledge there's no usage in C++/WinRT that requires Conformance Mode (/permissive-) or Two-Phase Name Lookup (enabled by /permissive-, turned off individually with /Zc:twoPhase-). It does require C++17 mode (/std:c++17). What operator names in particular are you referring to? – Garnish

Answer 2

I made a little patch to fix this problem. It adds a couple of forward declarations so necessary names could be found with two-phase lookup and a missing template keyword.

C:\Program Files (x86)\Windows Kits\10\Include\10.0.17134.0\cppwinrt\winrt\base.h

2171a2172,2189
>     template <typename D, typename I, typename Enable = void>
>     struct producer;
> }
> 
> WINRT_EXPORT namespace winrt
> {
>     template <typename D, typename I>
>     D* from_abi(I const& from) noexcept;
> 
>   template <typename I, typename D, std::enable_if_t<std::is_base_of_v<Windows::Foundation::IUnknown, I>>* = nullptr>
>     impl::abi_t<I>* to_abi(impl::producer<D, I> const* from) noexcept;
> 
>     template <typename I, typename D, std::enable_if_t<std::is_base_of_v< ::IUnknown, I>>* = nullptr>
>     impl::abi_t<I>* to_abi(impl::producer<D, I> const* from) noexcept;
> }
> 
> namespace winrt::impl
> {
6244c6262
<     template <typename D, typename I, typename Enable = void>
---
>     template <typename D, typename I, typename Enable>
6353c6371
<     template <typename I, typename D, std::enable_if_t<std::is_base_of_v<Windows::Foundation::IUnknown, I>>* = nullptr>
---
>     template <typename I, typename D, std::enable_if_t<std::is_base_of_v<Windows::Foundation::IUnknown, I>>*>
6359c6377
<     template <typename I, typename D, std::enable_if_t<std::is_base_of_v< ::IUnknown, I>>* = nullptr>
---
>     template <typename I, typename D, std::enable_if_t<std::is_base_of_v< ::IUnknown, I>>*>
7189c7207
<             return root_implements_type::get_weak<D>();
---
>             return root_implements_type::template get_weak<D>();

Banka