type_info is not exported correctly

[huangqinjin]

Run preprocessor on std.ixx and inspect its output:

>cl /EHsc /std:c++latest /P "%VCToolsInstallDir%\modules\std.ixx"
Microsoft (R) C/C++ Optimizing Compiler Version 19.40.33808 for x64
Copyright (C) Microsoft Corporation.  All rights reserved.

/std:c++latest is provided as a preview of language features from the latest C++
working draft, and we're eager to hear about bugs and suggestions for improvements.
However, note that these features are provided as-is without support, and subject
to changes or removal as the working draft evolves. See
https://go.microsoft.com/fwlink/?linkid=2045807 for details.

std.ixx

Search type_info in std.i from top, we see that the first statement is in eh.h

extern "C++" { // attach declarations to the global module, see N4910 [module.unit]/7
    class type_info;
} // extern "C++"

and later in vcruntime_typeinfo.h it is exported:

extern "C++" { 
export class type_info {};
}

I believe this violates https://eel.is/c++draft/module.interface#6

A redeclaration of an entity X is implicitly exported if X was introduced by an exported declaration; otherwise it shall not be exported.

[StephanTLavavej]

Thanks - I forgot to search VCRuntime for forward-declaring its own machinery. (This would be easier if MSVC enforced the Standard rule; I've got an active bug requesting that from the compiler team.)

[StephanTLavavej]

Created internal MSVC-PR-549242.

[StephanTLavavej]

Fix merged for VS 2022 17.11 Preview 3. Thanks again for the report! 😻