Re: [boost] [config] 'requres' doesn't take differing -std into account

Subject: Re: [boost] [config] 'requres' doesn't take differing -std into account
From: Edward Diener (eldiener_at_[hidden])
Date: 2015-06-21 21:11:02

On 6/21/2015 10:19 AM, Peter Dimov wrote:
> I have, in my user-config.jam,
>
> using gcc ;
>
> feature.subfeature toolset gcc : std : cxx0x cxx11 cxx1y cxx14 :
> optional composite propagated ;
>
> feature.compose <toolset-gcc:std>cxx0x : <cxxflags>-std=c++0x ;
> feature.compose <toolset-gcc:std>cxx11 : <cxxflags>-std=c++11 ;
> feature.compose <toolset-gcc:std>cxx1y : <cxxflags>-std=c++1y ;
> feature.compose <toolset-gcc:std>cxx14 : <cxxflags>-std=c++14 ;
>
> using clang : : : <cxxflags>-Wno-variadic-macros
> <cxxflags>-Wno-c99-extensions ;
>
> feature.subfeature toolset clang : std : cxx0x cxx11 cxx1y cxx14 :
> optional composite propagated ;
>
> feature.compose <toolset-clang:std>cxx0x : <cxxflags>-std=c++0x ;
> feature.compose <toolset-clang:std>cxx11 : <cxxflags>-std=c++11 ;
> feature.compose <toolset-clang:std>cxx1y : <cxxflags>-std=c++1y ;
> feature.compose <toolset-clang:std>cxx14 : <cxxflags>-std=c++14 ;
>
> This allows me to use toolset=clang (without -std) and
> toolset=clang-cxx11 (with -std=c++11).
>
> The 'requires' rule however caches the results of the configuration
> check when I run with toolset=clang, and then when I rerun with
> toolset=clang-cxx11, it uses the cached values, which is wrong.

I believe the same problem is causing predef-check problems in the 
predef library because I have seen local errors using predef-check which 
also says that a previous calculation on another toolset has been cached 
and is being reused, even when the toolset changes. Somehow the 
incorrect cached value is being retained by Boost Build even when the 
toolset value changes and a new calculation needs to be made. But like 
many other people I don't know nearly enough about Boost Build to figure 
out what it is doing.

>
> I use something like
>
> run test.cpp : : : [ requires cxx11_variadic_templates
> cxx11_template_aliases cxx11_hdr_type_traits cxx11_hdr_tuple ] ;