Request: CMake integration sets flags to same values as vcpkg builds

[arthur-tacca]

When vcpkg builds libraries, it chooses the command line switches for the compiler, with some options depending on the selected triplet. For example, it adds /Z7 so that debug symbols are generated even in release builds. But when you build a CMake project using the vcpkg toolchain, these command line options aren't set. I find this quite surprising - surely you want all parts of the project to be built in a consistent way, at least as a default? This is especially true if the project you're working on is a library that you're considering using from within vcpkg later.

The most significant impact of this (you probably saw this coming) is if you are building with a triplet like x64-windows-static that uses the static CRT. In that case the default compiler options will give you a mismatched CRT and probably a linker error or a runtime crash. As far as I can tell, in the absence of the requested feature, the correct command line to build a CMake project with static libraries is:

cmake ^
   -DCMAKE_TOOLCHAIN_FILE=%VCPKGDIR%\scripts\buildsystems\vcpkg.cmake ^
   -G "Visual Studio 15 2017 Win64" ^
   -DVCPKG_TARGET_TRIPLET=x64-windows-static ^
   "-DCMAKE_CXX_FLAGS_DEBUG=/D_DEBUG /MTd /Z7 /Ob0 /Od /RTC1" ^
   "-DCMAKE_CXX_FLAGS_RELEASE:STRING=/MT /O2 /Oi /DNDEBUG /Z7" ^
   ..

Even this doesn't cover all cases (e.g. it doesn't attempt to fix MinSizeRel or RelWithDebInfo, although I don't think vcpkg supports those anyway, and it only sets C++ flags not C flags). This is not exactly intuitive! It's not even mentioned in the docs (where those extra options are hidden in a "...").

Please could it possible (and, ideally, the default) for the vcpkg toolchain to set the compiler flags? I resisted making the title something like "Please make building static projects easier" because I don't just care about the /MT switch. Similarly, for consistentcy with vcpkg, dynamic-library-linking triplets should set -DBUILD_SHARED_LIBS=true.

Thanks for considering it.