On Wed, Jun 29, 2016 at 3:25 PM, Richard Smith <rich...@metafoo.co.uk> wrote:
> On Wed, Jun 29, 2016 at 12:14 PM, Nico Weber <tha...@chromium.org> wrote: > >> For clang-cl, we should follow cl's model of selecting a standard. Before >> C++17, this was "use newest language the compiler knows about" (keyed off >> -fmsc-version; clang-cl detects the system msvc version by default if >> that's not passed in). After C++17, there's an explicit language flag, and >> we use the same default as cl. >> > > Is that default something other than "the newest one"? > It looks like the next MSVC (which adds that flag) defaults to C++14. (See majnemer's r273841 which implemented this in clang-cl, and https://blogs.msdn.microsoft.com/vcblog/2016/06/07/standards-version-switches-in-the-compiler/ ) > Last I checked (which was a while ago), libstdc++ didn't parse with >> -std=c++14, at least at some version. I don't remember which version of >> libstdc++ I tried (maybe 4.9?). Should that factor into the decision? Not >> parsing standard library headers by default on Linux seems like a somewhat >> suboptimal user experience. >> > > Last time I looked into this, I saw only one problem with version 4.9: > libc doesn't provide ::gets to C++14, and earlier versions of libstdc++ > assume it's there and do "namespace std { using ::gets; }". We can add a > compatibility hack to clang to work around this. > > Note that at this point I'd like to mainly focus on what our policy should > be; > Fair enough. I don't have a strong opinion on that; your proposal makes sense to me. (Except for clang-cl, which I think needs to mirror what cl does.) > there are certainly technical challenges involved in actually applying the > policy (another one is that clang's test suite still has some failures when > the default is changed, but Charles Li has made tremendous headway on > this), and if we can't actually prepare for the transition in the C++ > default in time for 3.9, then so be it. > > >> On Wed, Jun 29, 2016 at 3:09 PM, Richard Smith via cfe-commits < >> cfe-commits@lists.llvm.org> wrote: >> >>> Hi all! >>> >>> I'd like to establish a policy for Clang's default language standard (if >>> none is specified with -std), as follows: >>> >>> Clang defaults to the most recent published standard for the selected >>> language that it fully implements. >>> >>> The practical impact of this is that clang++ will default to C++14 for >>> C++ compilations (for version 3.9 onwards) and will default to C++17 once >>> our implementation support is complete and the standard is published >>> (whichever happens later). >>> >>> I'd suggest that we apply the same policy for clang-cl, but if it's >>> important that we enable a not-yet-fully-implemented standard for cl >>> compatibility, that seems reasonable. >>> >>> The question of whether the default mode for the GCC-compatible driver >>> should be -std=gnuXXX or -std=cXXX is separate, but also likely worth >>> discussing. Enabling GNU keywords by default is a very odd choice, and if >>> we believe we can change our defaults without breaking the world then this >>> seems like a good time to do so. >>> >>> I also intend to make explicit in our documentation that our -std=XXX >>> flag enables the selected standard, *plus all relevant issues in Defect >>> Report status from the relevant language committee* (it doesn't make sense >>> to support a language without its bugfixes). >>> >>> Thoughts? >>> >>> _______________________________________________ >>> cfe-commits mailing list >>> cfe-commits@lists.llvm.org >>> http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits >>> >>> >> >
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