Conan package: build failure using c++17 (or later) with MSVC.

[Vincent Saulue-Laborde]

Description

While trying to use thorvg via conan in a c++20 project on Windows (Visual Studio Community 17.9.3), the thorvg build fails with the following first error:

C:\Program Files (x86)\Windows Kits\10\Include\10.0.22621.0\shared\rpcndr.h(203,9): error C2872: 'byte': ambiguous symbol [C:\Users\Vincent\.conan2\p\b\thorvd6d3916f25a7e\b\build-debug\src\25a6634@@thorvg@
sta.vcxproj]
  (compiler le fichier source '../../src/src/loaders/ttf/tvgTtfLoader.cpp')
  C:\Program Files (x86)\Windows Kits\10\Include\10.0.22621.0\shared\rpcndr.h(202,23):
  could be 'unsigned char byte'
  D:\Programmes\Microsoft Visual Studio\2022\Community\VC\Tools\MSVC\14.39.33519\include\cstddef(34,24):
  or       'std::byte'

My conan host profile:

[settings]
arch=x86_64
build_type=Debug
compiler=msvc
compiler.cppstd=20
compiler.runtime=dynamic
compiler.runtime_type=Debug
compiler.version=193
os=Windows
[conf]
tools.cmake.cmaketoolchain:generator=Ninja Multi-Config

Reproduction steps

1. Open a Visual Studio command prompt
2. cd to an empty folder you don't mind polluting
3. conan remove thorvg
4. conan install --requires="thorvg/0.13.0" --build=missing -s:h build_type=Debug -s:h compiler.cppstd=20

Full build output

Root cause ?

The C++ standard library provides std::byte since C++17. The Windows header rpcndr.h defines typedef unsigned char byte;. A using namespace std; in thorvg causes these types to be ambiguous.

Workaround for users

Force conan to build the thorvg dependency in C++14 for your project, to "undefine" std::byte. This can be done by adding -s thorvg/*:compiler.cppstd=14 in the conan install command of your project:

# Build the project's dependencies with C++20 by default, but use C++14 for thorvg.
conan install . -pr:b cpp20-release -pr:h cpp20 -s build_type=Debug --build=missing -s thorvg/*:compiler.cppstd=14

[rinechran]

Thank you for raising the issue
Due to build errors caused by the definition overlap between std::byte introduced in C++17 and byte in windows.h, I will resolve this issue by adding the macro #define _HAS_STD_BYTE 0.

[vtorri]

just don't include all the headers from windows.h. Just before windows.h in tvgTtfLoader.cpp (and probably in all the source/header files which include windows.h), define WIN32_LEAN_AND_MEAN like that:

#ifndef WIN32_LEAN_AND_MEAN
#  define WIN32_LEAN_AND_MEAN
#endif
#include <windows.h>
#undef WIN32_LEAN_AND_MEAN

it works for me on mingw when using c++20.

[rinechran]

thank you for your suggestion. If it is possible to resolve this with the WIN32_LEAN_AND_MEAN macro , this solution seems preferable

thank you for your suggestion. If it is possible to resolve this with the WIN32_LEAN_AND_MEAN macro , this solution seems preferable

[Hermet Park]

@vsaulue Hello, the fix will be applied in v0.13.3. With the version, it will insert the addressed the definition - WIN32_LINEA_AND_MEAN in thorvg "config.h"

Please let us know if you have any trouble with the solution. Thanks.

[Vincent Saulue-Laborde]

Hi @hermet,

I don't see a conanfile.py in the repo to test the Conan packaging, so I tested the build directly with git clone and meson instead. I was able to reproduce the errors on v0.13.2, and they are effectively gone on the main branch, so it looks good.

Thanks for the quick fix !