[question] Setting common flags across build types with CMakeToolchain in multi-config generators about conan HOT 1 OPEN

Hi @solarispika

Thanks for your question, and thanks for your good research, including the merge request to CMake.

However, this experience led me to wonder if it is possible to assign CMAKE_FLAGS (instead of CMAKEFLAGS) in the CMakeToolchain when using a multi-config generator. There might be cases where users need common flags shared across build types, such as the -Werror flag.

This is a good point. The issue is that the current mechanisms don't have any way to model this, when defining something, from the the profile, command line, everything is tied to the current configuration, because there is no way to differentiate that. Things like tools.build:cxxflags passed in a profile belong to the build_type/configuration of that profile.
To be able to make them common to all configurations, we would need something like tools.build:cxx_flags_common, but I'd say this looks a bit ugly.

Conan has mechanisms to share information, so if the same cxxflags are to be used for multiple configurations, it can be reused in its own profile file, and include() from other profiles wanting to use it. If CMake could handle that correctly, that would be the cleanest solution. My understanding is that in multi-config IDEs like VS, there is actually not a common set of flags in a common .props file, but just the same flags that are applied to the different configurations, repeating them.

from conan.