since we dropped the support of xenial, we now have the luxury of using
newer CMake! and by using CMake 3.10.2, we can prevent libfmt from
assuming that we are using C++11, and hence set `CMAKE_CXX_STANDARD` to
11, which will literally append `-std=gnu++11` to `CMAKE_CXX_FLAGS`.
the last `-std` option passed to `g++` takes precendence.
since we've switched over to C++17, and we are using C++17 features.
so, using cmake older than 3.8 breaks the build. because it is CMake 3.8
which stared support `CMAKE_CXX_STANDARD` 17.
- for bionic: https://packages.ubuntu.com/bionic/cmake : 3.10.2
- for CentOS7:
https://dl.fedoraproject.org/pub/epel/7/x86_64/Packages/c/ : 3.13.5
so in this change,
* bump up the required version to v3.10.2
* cleanups to wipe out the workaround for lower CMake versions
* use `PROJECT_VERSION` defined by `project()` command instead of
`VERSION` explicitly defined.
Signed-off-by: Kefu Chai <kchai@redhat.com>
before this change, we fails to detect std::filesystem with clang++,
because the cmake project created by try_compile() only expands
following options passed from its caller:
- COMPILE_DEFINITIONS
- INCLUDE_DIRECTORIES
- LINK_DIRECTORIES
- LINK_LIBRARIES
which do not include CMAKE_CXX_FLAGS, so either we need to (ab)use
COMPILE_DEFINITIONS for passing -std=c++17, or we can change the
CMAKE_CXX_FLAGS in the parent env, as it turns out the created cmake
project does inherit this flag from current project. in this change,
we use the COMPILE_DEFINITIONS approach: simpler this way. and we
can drop it once cmake 3.8 is required.
Signed-off-by: Kefu Chai <kchai@redhat.com>
see
https://libcxx.llvm.org/docs/UsingLibcxx.html#using-libc-experimental-and-experimental,
> Note that as of libc++ 7.0 using the <experimental/filesystem>
> requires linking libc++fs instead of libc++experimental.
do not build ceph_test_admin_socket_output if we are not able to find
the library for std::experimental::filesystem . it is a workaround of
https://reviews.freebsd.org/D10840 where FreeBSD 11.2 does not ship
libc++experimental.a .
Signed-off-by: Kefu Chai <kchai@redhat.com>
