C++ modules conformance

[kennykerr]

Now that Visual C++ 16.5 Preview 2 has decent support for C++ modules, I'm able to once again tweak C++/WinRT to support C++ modules as an alternative to precompiled headers. This is still experimental as there remain some minor issues, but it is getting very close.

The cppwinrt.exe compiler will now generate a winrt/winrt.ixx file that may be compiled as a module as follows:

cl /c /I . /experimental:module /EHsc /bigobj /std:c++17 /await winrt/winrt.ixx

This will compile all of the projected namespaces into a single winrt module. This step takes quite a while - around 2 minutes on my machine. But once that's built, much like a PCH, you can import the module into any (compatible) TU very quickly as follows:

cl /experimental:module /EHsc /std:c++17 /await app.cpp winrt.obj

Here's a sample app that you can use to test this:

import winrt;
#include <stdio.h>

#pragma comment (lib, "oleaut32")

// Note: these two are only needed when compiling with modules.
#pragma comment (lib, "ole32")
#pragma comment (lib, "advapi32")

using namespace winrt;
using namespace Windows::Foundation;

int main()
{
    Uri uri(L"http://kennykerr.ca");
    printf("%ls\n", uri.Domain().c_str());
}

Note the extra libs that are required when compiling with modules. This is a C++ compiler bug.

There's also an issue with coroutines - waiting for a solution from the C++ team.

[Scottj1s]

nice!

[mediabuff]

Great! Another optimization that can help is to separate the platform header generation and app header generation - as the former changes infrequently. Additionally, if the platform headers can be shared across projects - this will help in the build speeds as well.

[mediabuff]

I tried it with the new pull.

1>------ Build started: Project: cppwinrt_modules, Configuration: Debug Win32 ------
1>winrt.ixx
1>d:\agent_work\8\s\src\vctools\Compiler\CxxFE\sl\p1\c\module\writer.cpp:5261: sorry: not yet implemented
1>c:\temp\cppwinrt_modules\cppwinrt_modules\Debug\Generated Files\winrt\winrt.ixx(491,1): fatal error C1001: Internal compiler error.
1>(compiler file 'd:\agent_work\8\s\src\vctools\Compiler\CxxFE\sl\p1\c\module\utilities.h', line 39)
1> To work around this problem, try simplifying or changing the program near the locations listed above.

Here is the cl command line:
CL.exe /c /I. /I"Debug\Generated Files\" /I"C:\MyDevProjects\MyProjectsThirdPartyLibs\vcpkg\installed\x86-windows\include" /ZI /JMC /nologo /W4 /WX- /diagnostics:column /Od /Oy- /D WIN32 /D _DEBUG /D _CONSOLE /D WIN32_LEAN_AND_MEAN /D WINRT_LEAN_AND_MEAN /D _UNICODE /D UNICODE /Gm- /EHsc /RTC1 /MDd /GS /fp:precise /Zc:wchar_t /Zc:forScope /Zc:inline /std:c++latest /Fo"Debug\" /Fd"Debug\vc142.pdb" /Gd /TP /wd4100 /analyze- /FC /errorReport:prompt /bigobj /await /EHsc /experimental:module /bigobj /await /permissive- /bigobj "Debug\Generated Files\winrt\winrt.ixx"

[kennykerr]

@mediabuff You need to use Visual C++ 16.5 Preview 2 or later.

[mediabuff]

Actually, it 16.5/P2. But may be it's related to this error;

' c:\temp\cppwinrt_modules\cppwinrt_modules\main.cpp(1,13): error C2235: mismatching target architecture for compiled module interface for 'winrt' from 'winrt.ifc'
1> c:\temp\cppwinrt_modules\cppwinrt_modules\main.cpp(1,13): error C2230: could not find module 'winrt''

[kennykerr]

Could be. It looks like you're trying to build this from the IDE. I would suggest following the instructions exactly as I demonstrated above from a single dev command prompt. Keep in mind that C++ module support is still very new and experimental.