https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86934
--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> --- (In reply to Jonathan Wakely from comment #0) > The current <version> header doesn't account for the fact that many features > are not defined for freestanding builds. > > Also, the --enable-libstdcxx-filesystem-ts configure option means that > <filesystem> isn't always present, even for hsoted builds (but that should > change for GCC 9 anyway). That was PR 86756 and is fixed now. > I'm not sure how to do this cleanly so that <version> is always consistent > with the real values in other headers. We could generate <version> from a > script that processes the headers (separately for freestanding and hosted > headers) and just extracts the __cpp_lib_* macros and the preprocessor > conditions they depend on. Or maybe just a script that generates the file from input like: filesystem 201703 c++17 launder 201606 c++17 _GLIBCXX_HAVE_BUILTIN_LAUNDER shared_timed_mutex 201402 c++14 _GLIBCXX_HAS_GTHREADS > Also, in https://gcc.gnu.org/ml/libstdc++/2018-07/msg00128.html I said: > > It would be nice if we had tests to check that every macro in > <version> matches the other definition of it (i.e. either both are > defined to the same value, or neither is defined). That should be simple, just include <bits/stdc++.h> and <version> and compile with -Wsystem-headers to check for redefinition warnings.
