Fix compiling python_uwp.cpp with clang-cl on Windows

[chris-eibl]

clang-cl fails with the following error when compiling python_uwp.cpp:

1>In file included from ..\PC\python_uwp.cpp:14:
1>In file included from C:\Program Files (x86)\Windows Kits\10\Include\10.0.26100.0\cppwinrt\winrt\Windows.ApplicationModel.h:9:
1>In file included from C:\Program Files (x86)\Windows Kits\10\Include\10.0.26100.0\cppwinrt\winrt/base.h:56:
1>C:\Program Files\Microsoft Visual Studio\2022\Community\VC\Tools\MSVC\14.43.34808\include\experimental/coroutine(29,2): error : The <experimental/coroutine>, <experimental/generator>, and <experimental/resumable> headers do not support Clang, but the C++20 <coroutine> header does.

Let's fix it using

#if defined(__clang__)
#define _SILENCE_CLANG_COROUTINE_MESSAGE
#endif

before including the respective header.

This only happens when IncludeUwp is set in case of building with build.bat or in the Visual Studio IDE, because there always all projects are built.

Linked PRs

• GH-131291: fix building python_uwp.cpp with clang-cl #131292

[encukou]

Will this result in a working “uwp” build?
Could IncludeUwp be unset on clang instead? (That's a naive question, I don't know much about how PCbuild works.)

Could you add a source comment about why this is needed, perhaps with a link to docs about _SILENCE_CLANG_COROUTINE_MESSAGE?

[chris-eibl]

Will this result in a working “uwp” build?

Yes. At least a quick test I did is working: enable developer mode so that local UWP apps can be run. Starting the app then gives me

Python 3.14.0a6+ (heads/fix_clangcl_sysmodule-dirty:0eea635960, Mar 17 2025, 08:32:10) [Clang 19.1.1 ] 64 bit (AMD64) with MSC v.1943 CRT] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>>

Could IncludeUwp be unset on clang instead? (That's a naive question, I don't know much about how PCbuild works.)

You already have to opt-in by setting it when doing a "regular" build.bat. Only in the Visual Studio IDE it is compiled by default.

In the latter, you could opt-out via deselecting it in the Configuration Manager.

Could you add a source comment about why this is needed, perhaps with a link to docs about _SILENCE_CLANG_COROUTINE_MESSAGE?

This comes directly out of the MSVC STL header: https://github.com/microsoft/STL/pull/136/files.
python_uwp.cpp doesn't need it, so it's safe to deactivate it. Would you like me to put that link as a comment above the define in the PR?

[zooba]

I would probably tend towards disabling IncludeUwp on Clang, or just ignoring the warning. Whichever way PEP 773 goes, I'm hopeful that this entire project will go away soon enough.

[zooba]

Or the PR was already there I guess, so easy enough to just merge it.

[chris-eibl]

Thanks for merging. This one wasn't a warning but an error. Sorry for not being explicit here.
Too much scrolling would have been needed to see it in the issue, so I am reformatting that part here:

1>C:\Program Files\Microsoft Visual Studio\2022\Community\VC\Tools\MSVC\14.43.34808\include\experimental/coroutine(29,2):
error : The <experimental/coroutine>, <experimental/generator>, and
<experimental/resumable> headers do not support Clang, but the C++20 <coroutine> header does.