Hi everyone, I would like to discuss a system-wide way to handle C++ standard setting in Gentoo. We currently have many packages appending -std=c++XX to their flags, and it's hard to keep track of which packages use which version of the standard. This is a problem when packages force dependencies to use the same version of the standard, or if certain combinations cause ABI or other breakage (i.e., due to backports conflicting with standard classes). We currently have the page below with some documentation, but I have not found much else on the topic: https://wiki.gentoo.org/wiki/Project:C%2B%2B/Maintaining_ABI
One problem is that depending on the compiler version, the right option may change (e.g. -std=c++1y vs -std=c++14 and -std=c++1z vs -std=c++17). This isn't a big problem when using recent compilers, but may be it will if you want to test some package you develop with an older compiler you still need to support (out of Gentoo), or if you use ICC, which lags a bit behind in standards support. For CMake projects, we could set CMAKE_CXX_STANDARD in cmake-utils.eclass. For other projects we could use other means. In any case, it might make sense to have global USE flags like c++11 (already a local USE flag), c++14, etc, along with a small eclass that C++ projects can inherit to get the right setting instead of using append-cxxflags with a hard-coded standard version. Hard-coding the standard flag may create problems because we will have a mix of the default and the hard-coded ones. The USE flags would also allow depending on a package with the same standard configuration or setting the standard globally to something different than the compiler default (i.e. either stay with C++11 because that's what you need to work with, or use C++17 since you are on ~arch and your system compiler supports it, etc). What are your thoughts on the matter? This has been discussed in the past¹, but it doesn't seem we have a global solution yet. I think another discussion happened more recently, but I didn't find the thread. Cheers, —Guilherme 1. https://archives.gentoo.org/gentoo-dev/message/eab0dc92cb8adb1457ff368c5a033eaf
