please remove target_compile_features from INTERFACE

[ObiWahn]

The automatically appended --std=gnu++11 overrides the --std=c++1z of my project. It is a shame that cmake does not support unfinished standards.

[ObiWahn]

I did a bit research on this:

• since cmake 3.8 c++17 is supported
• target_compile_features(mylib INTERFACE cxx_std_17) in the including target should fix the problem
• set(CMAKE_CXX_STDANDARD 17) in the including project fixes the problem
• the patch below could work for most people using CMake below v3.8

list(FIND "${CMAKE_CXX_FLAGS}" "-std=c++1z" use1z)
list(FIND "${CMAKE_CXX_FLAGS}" "-std=c++17" use17)
if(use1z LESS 0 AND use17 LESS 0)
# CMAKE_CXX_STANDARD 17 - is availalbe with cmake 3.8
# if the including project defines the correct standard
# this check should not be required

# mpl requires a number of features to compile, this will automatically set the c++ standard version
# to support those features. The c++ version is not explicitly set, so that cmake can figure
# things out by itself
target_compile_features(kvasir_mpl INTERFACE
        cxx_variadic_templates
        cxx_constexpr
        cxx_alias_templates
        cxx_auto_type
        cxx_long_long_type
        cxx_right_angle_brackets
        cxx_static_assert
        cxx_uniform_initialization
        cxx_user_literals
        ${CPP_EXTRA_FEATURES})
endif()

[chieltbest]

I agree that we should probably conditionally remove the compile features as I have had problems with it as well, however I wonder if it wouldn't be better to search for "-std=" instead, as that would also include other versions.
Just checking the opinion on this as it might create some problems instead that I don't know of.

[ObiWahn]

I would try to upgrade to 3.8. For versions below setting the flag is the only way to get c++17 support, from my perspective it is the only valid usage of the flag (-std=...) as part of CMAKE_CXX_FLAGS. That is why I did not consider other possible combinations. The "gnu" versions of the flags should probably be checked as well.