On Wed, Aug 10, 2022 at 8:35 AM kefu chai <tchaikov@xxxxxxxxx> wrote: > > hi folks, > > as you might have already noticed, we've made the switch to C++20. see > Casey's mail sent to this mailing list a couple days ago. > > another thing you need to pay attention to is, we now need to use at > least gcc-11 or clang-12 for compiling the tree. > > if your working flows depend on the stock C++ compiler in your distro, > you might need to check the version to make sure that its C++20 > support. see also > https://en.cppreference.com/w/cpp/compiler_support#cpp20 . for > instance, if you are using ubuntu focal, you could use the ppa repo at > https://launchpad.net/~ubuntu-toolchain-r/+archive/ubuntu/test or > prebuilt clang-12 or up at https://apt.llvm.org. if you are using > centos/RHEL 8, you might want to use gcc-toolset-11 or gcc-toolset-12 > or llvm-toolset-12 . > > apparently, we are not using all the C++20 features, but we are > starting exploring some of them. as some of us have noticed, we have > started using https://wg21.link/P1185R2 in the main branch. because we > are now using both gcc-11 and clang-12 in our CI/CD workflows, we can > assure you that these two compilers should be able to compile the main > branch. > > i apologise for any inconvenience caused. > > cheers, > > -- > Regards > Kefu Chai > _______________________________________________ > Dev mailing list -- dev@xxxxxxx > To unsubscribe send an email to dev-leave@xxxxxxx > thanks Kefu, there was some good discussion on the topic in today's ceph leadership call, and i wanted to share my thoughts here in more detail # c++20 features and compiler versions compiler support for c++20 features are tracked by gcc and clang: https://gcc.gnu.org/projects/cxx-status.html#cxx20 https://clang.llvm.org/cxx_status.html#cxx20 as you can see, feature support is spotty and we still don't have *full* support in the latest compiler versions. this makes it difficult for the ceph project to draw a line Kefu did a lot of testing and settled on gcc11 and clang12 as the minimum compiler versions, so those are the versions we're using in ceph's CI. these may change in the future, but the vague answer to questions about whether we can use a particular c++20 feature is 'yes if it builds in CI'. there may be some cases where a feature builds with gcc but not with clang, but this is nothing new - we'll just have to continue dealing with those as they come up # distros and default compiler versions ceph has been supporting centos 8 and ubuntu 20.04 for a long time, and their default compiler versions are really old by now. as Ken just announced in 'linux distro requirements for reef', the reef release will target centos stream 9 and ubuntu 22.04, so development on the 'main' branch should switch asap. Kefu and David have been working hard to add these distros to our CI, and it sounds like ubuntu 22.04 is just about ready. if you're interested in helping with this, i'd encourage you to reach out in #sepia irc # ceph's cmake https://github.com/ceph/ceph/pull/45133 merged last week, which raised the CMAKE_CXX_STANDARD from 17 to 20. unfortunately, because c++20 support is so fuzzy, cmake doesn't actually enforce a minimum compiler version. as a result, developers using their default compilers started seeing build failures after the merge of https://github.com/ceph/ceph/pull/47427 which introduced the first use of the c++20 spaceship operator i know that it's frustrating to see your development builds start failing because of changes like this, without any clues to resolve them. i'd like to find a way to turn these compilation failures into an obvious cmake error message that offers additional guidance cmake does have some granular control over language feature support with https://cmake.org/cmake/help/latest/command/target_compile_features.html. hypothetically, that would allow us to do something like 'target_compile_features(ceph-common PUBLIC cxx_spaceship)' to require a compiler version that supported c++20's spaceship operator. however, https://cmake.org/cmake/help/latest/prop_gbl/CMAKE_CXX_KNOWN_FEATURES.html doesn't list any features past c++14. so instead i'm proposing in https://github.com/ceph/ceph/pull/47543 that we add an explicit check for compiler versions, with error messages that make it clear exactly what compiler version is required is there more we should do to ease this transition? let me know what you think _______________________________________________ Dev mailing list -- dev@xxxxxxx To unsubscribe send an email to dev-leave@xxxxxxx
