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

Subject: [boost] Attn: Volodya.. Re: [config] 'requres' doesn't take differing -std into account
From: Rene Rivera (grafikrobot_at_[hidden])
Date: 2015-06-21 21:27:15

On Sun, Jun 21, 2015 at 8:11 PM, Edward Diener <eldiener_at_[hidden]>
wrote:

> 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 must confess I don't know the rationale for limiting the feature set for
config checks. We have to see what Volodya says about this.

-- 
-- Rene Rivera
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