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

From: pbristow_at_[hidden]
Date: 2020-02-12 17:17:48

> -----Original Message-----
> From: Boost <boost-bounces_at_[hidden]> On Behalf Of Edward Diener via
> Boost
> Sent: 12 February 2020 16:00
> 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 2/12/2020 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.over
> >>> vi
> >>> 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.

Correct!

>b2 toolset=gcc cxxstd=17-gnu float128_snips

Neat - but I am not sure how I would have guessed, (without delving into .jam src).

>b2 toolset=gcc toolset-version=9.2.0 cxxstd=17 float128_snips  fails.

In the end it feels all too clever, mainly to reduce typing.

I am not surprised to find that toolset=gcc-gnu doesn't work.

> > Examples, examples ...

Are very helpful, as I have been bleating for over a decade.

Thanks

Paul