Mathias, On Tue, Oct 10, 2017 at 12:25 PM, Matthias Klose <d...@debian.org> wrote: > On 10.10.2017 11:42, Mathieu Malaterre wrote: >> On Tue, Oct 10, 2017 at 11:38 AM, Matthias Klose <d...@debian.org> wrote: >>> On 10.10.2017 08:45, Mathieu Malaterre wrote: >>>> Dear all, >>>> >>>> Since the GCC 6 release [1], the default mode for C++ is now >>>> -std=gnu++14 instead of -std=gnu++98. What this means is that upon >>>> (re)compilation a library written for c++98 will be recompiled using a >>>> different c++ standard (c++14 in this case), unless of course the >>>> upstream package explicitly set the -std= flags with the appropriate >>>> c++ version. >>>> >>>> The ISO committee generally describe the change in between different >>>> standards [2] and in some case, one can find examples of subtle change >>>> in behaviors [3] and [4]. >>>> >>>> With this mind I'd like to make mandatory the -std=c++XY flags when >>>> compiling either a c++ library or a stand-alone c++ program: >>>> >>>> 1. Either upstream define the explicit -std=c++XY flags by mean of its >>>> build system, >>>> 2. Or the package maintainers needs to explicit change the CXXFLAGS to >>>> pass the appropriate version of the c++ standard. In which case this >>>> should be documented in the README.Debian file. >>>> 3. As a fallback, dh should initialize the CXXFLAGS with -std=gnu++98 >>>> >>>> If there is a consensus on the following change, I'll go ahead and >>>> also file a bug for lintian to scan the compilation logs in search for >>>> missing -std=c++ expression when g++ command line are issued. >>> >>> I don't think this is a good idea, and I'm still trying to understand what >>> problem you are trying to solve. It took a while until GCC had stable c++11 >>> support, and now you want to fallback to a 20 year old standard by default? >> >> As said above, this is simply a fallback, I am fine with any value as >> long as I can see it in the log clearly. >> >> My point was about making the flag *explicit*, whatever value is >> chosen, so that upon recompilation we gets the same symbols, the same >> behavior, no FTBFS (because of deprecated feature). > > Various libraries do error out on deprecated functions/macros, which you can > override by preprocessor macros. This is usually done in the package. Why > should that be different for the compiler? > >>> It would be better to spend some time to prepare for -std=gnu++17 instead ;) >> >> So you have no major objection against my proposal, > > No, I have objections, because after a while this will become a debt to > maintain ...
Thanks for taking the time to answer. As with Gert's answer, I fail to understand your point: You would prefer to see packages being (re)compiled *without* an explicit -std= flag, so that it always gets recompiled using whatever is the current c++ standard used by gcc, correct ? >> I feared you may >> have an issue with mixed combination of stdc++ runtime lib (not sure >> exactly how this is handled at low level). > > There's only one runtime library in use. Yes, there are more or less subtle > issues which we address by library package renames for issues we cannot or do > not want to handle by renaming libstdc++ itself. But it's always the same > runtime library used, independent of the standard. Ah nice. I may be slamming open door, but could you confirm that you see no objection in maintaining a complex stdc++ package where the c++98 ABI (eg. std::string) will not be used by any packages in the near future.