RTTI dependency added by std::any

vongkitt commented 1 year ago

Description

When compiling with -fno-rtti using clang, ninja on VS 2022 17.4.3 the build will fail.

This line seems to be causing the issue:

#if defined(JSON_HAS_CPP_17)
    #include <any>
    #include <string_view>
#endif

Including any requires rtti to be on.

This error was produced using ninja and the VS 2022 17.4.3 clang compiler.

C:\Program Files\Microsoft Visual Studio\2022\Professional\VC\Tools\MSVC\14.34.31933\include\any(22,2): error GDF32A4F7: class any requires static RTTI.

  #error class any requires static RTTI.

   ^

Reproduction steps

Build using ninja and -fno-rtti and the VS 2022 17.4.3 clang compiler.

Expected vs. actual results

Expect: compilation successful Actual: #error class any requires static RTTI.

Minimal code example

No response

Error messages

No response

Compiler and operating system

MSVC 17.4.3

Library version

3.11.2

Validation

[ ] The bug also occurs if the latest version from the develop branch is used.
[ ] I can successfully compile and run the unit tests.

nlohmann commented 1 year ago

This is odd. Does the standard require std::any to only work with RTTI?

barcode commented 1 year ago

It should not. See SO, example using gcc 8.1, example using clang 8,

This might be an issue with the MSVC STL.

nlohmann commented 1 year ago

Thanks - maybe you can open an issue at https://github.com/microsoft/STL/issues ?

barcode commented 1 year ago

Well i did some more testing and am not so sure this is the issue... It seems msvc 19.14 is fine with std::any and disabled RTTI.

vongkitt commented 1 year ago

@barcode Were you using the clang-cl compiler builtin with VS ?

barcode commented 1 year ago

@vongkitt No, I don't have windows and hence i am using godbolt.org for my tests and this way i can share them here. I don't think godbolt has any msvc-clang option.

The strange thing about all of this: The Linux version clang is fine with using std::any when deactivating rtti while the msvc-clang is not.

Looking at the path in your error message

C:\Program Files\Microsoft Visual Studio\2022\Professional\VC\Tools\MSVC\14.34.31933\include\any

This looks like the msvc stl. If you open the <any> file, you probably can see the Microsoft Copyright. This would confirm my hunch.

Also there is a similar issue with any and static rtti: https://github.com/microsoft/STL/issues/3114

vongkitt commented 1 year ago

@barcode Yes MS built-in clang version is using the MS STL by default so your hunch is correct

nlohmann commented 1 year ago

Is this related to #4046?

ambiennt commented 1 year ago

Is this related to #4046?

Yes. #4096 fixes compiling with Clang-cl & -fno-rtti in combination with Microsoft STL.

nlohmann / json