Re: If one specifies a cxxstd-dialect, one must also specify the cxxstd

From: Edward Diener (eldiener_at_[hidden])
Date: 2020-02-12 15:59:45

On 2/12/2020 5:15 AM, Paul A Bristow via Boost wrote:
> 
> 
>> -----Original Message-----
>> From: Boost <boost-bounces_at_[hidden]> On Behalf Of Edward Diener via
>> Boost
>> Sent: 11 February 2020 18:32
>> To: boost_at_[hidden]
>> Cc: Edward Diener <eldiener_at_[hidden]>
>> Subject: Re: [boost] If one specifies a cxxstd-dialect, one must also specify the
>> cxxstd
>>
>> On 2/11/2020 4:56 AM, Paul A Bristow via Boost wrote:
>>> https://boostorg.github.io/build/manual/develop/index.html#bbv2.overvi
>>> ew.builtin
>>> s.features
>>>
>>> says
>>>
>>> 5.3. Builtin features
>>>
>>> cxxstd  Allowed values: 98, 03, 0x, 11, 1y, 14, 1z, 17, 2a, latest.
>>>
>>> cxxstd-dialect  Allowed values: iso, gnu, ms.
>>>
>>> So these work as expected
>>>
>>>     toolset=gcc cxxstd=2a cxxstd-dialect=gnu              is OK
>>>     toolset=gcc-9.2.0 cxxstd=2a cxxstd-dialect=gnu              is OK too
>>>
>>> But if I do NOT specify the cxxstd version - just
>>>
>>>      toolset=gcc cxxstd-dialect=gnu
>>>
>>> for example:
>>>
>>> boost\libs\multiprecision\example>b2 float128_snips toolset=gcc-8.1.0
>>> cxxstd-dialect=gnu address-model=64 release >
>>> .mp_float128_snips_gcc810_14_gnu.log
>>>
>>> Iboost/tools/build/src/build\feature.jam:1020: in
>>> feature.compress-subproperties from module feature
>>> error: assertion failure: [ set.equal "<cxxstd-dialect>gnu"
>>> "<toolset-gcc:version>8.1.0" : "<toolset-gcc:version>8.1.0" ]
>>> error: Expected: [ "true" ]
>>> error: Got: [ ]
>>>
>>> which had be puzzled for a while.
>>>
>>> Probably the even more common case of only having one compiler, say
>>> gcc, installed, and so not specifying toolset at all, confusingly
>>> behaves the same way?
>>>
>>> This is a perfectly reasonable behaviour, but this requirement might
>>> helpfully be documented.
>>>
>>> Or this more subtle than I understand?
>>
>> "dialect" is a sub-feature of "cxxstd" in the same way that "version" is a sub-feature
>> of "toolset". If you specify a sub-feature the feature to which it applies must
>> always be specified somewhere.
> 
> I did say " perfectly reasonable behaviour" 😉
> 
>   but if you say toolset=gcc you get a default version, and there isn't a command toolset-version=9.2, so the syntax isn't quite regular (and conveniently cleverer to you can write gcc-9.2.0 ...)

If you say cxxstd=xx you get a default dialect. Are you sure that you 
can not say toolset=gcc toolset-version=9.2 ? The "gcc-9.2.0" is 
shorthand for "toolset=gcc-9.2.0" since Boost Build especially 
recognizes toolset designations without the need of "toolset=" syntax. 
You should be able to say "cxxstd=17-gnu" as an example, in order to 
specify both as feature-subfeature.

> 
> Examples, examples ...?
> 
> Paul