Setting a feature for specific subsets based on an external condition

Hallo,
In order to build Boost.Serialization with some compilers
the path to an
external installation of Spirit must be specified on the
command line before
$(BOOST_ROOT). One way to achieve that is to ensure that
<cxxflags>-I/path/to/spirit is defined.

To ensure that Serialization builds with all the supported
toolsets I'd like to
define <cxxflags> as above only for the toolset that
require it and only if
$(SPIRIT_ROOT) is defined.

I had thought of writing a rule that took the toolset as
argument and checked
whether <cxxflags> was needed, roughly as follows
(pseudo bjam code):

rule include-spirit ( toolset )
{
  local SPIRIT_ROOT = [ modules.peek : SPIRIT_ROOT ] ;
  if ( $(SPIRIT_ROOT) && $(toolset) in borland vc cw
)
  {
    return
<toolset>$(toolset):<cxxflags>-I$(SPIRIT_ROOT) ;
  }
}

To be used as (pseudo bjam code again):

lib boost_serialization 
        : $(SOURCES).cpp
	:
<link>shared:<define>BOOST_SERIALIZATION_DYN_LIN
K=1
	  include-spirit
	:
	:
<link>shared:<define>BOOST_SERIALIZATION_DYN_LIN
K=1
	;

However I don't know the correct way to do it and I couldn't
find an example to
copy from....

Thank you,
Nicola Musatti


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On Wednesday 22 November 2006 18:29, Nicola Musatti wrote:
> Hallo,
> In order to build Boost.Serialization with some
compilers the path to an
> external installation of Spirit must be specified on
the command line
> before $(BOOST_ROOT). One way to achieve that is to
ensure that
> <cxxflags>-I/path/to/spirit is defined.
>
> To ensure that Serialization builds with all the
supported toolsets I'd
> like to define <cxxflags> as above only for the
toolset that require it and
> only if $(SPIRIT_ROOT) is defined.
>
> I had thought of writing a rule that took the toolset
as argument and
> checked whether <cxxflags> was needed, roughly as
follows (pseudo bjam
> code):
>
> rule include-spirit ( toolset )
> {
>   local SPIRIT_ROOT = [ modules.peek : SPIRIT_ROOT ] ;
>   if ( $(SPIRIT_ROOT) && $(toolset) in borland
vc cw )
>   {
>     return
<toolset>$(toolset):<cxxflags>-I$(SPIRIT_ROOT) ;
>   }
> }
>
> To be used as (pseudo bjam code again):
>
> lib boost_serialization
>
>         : $(SOURCES).cpp
> 	:
> 	:
<link>shared:<define>BOOST_SERIALIZATION_DYN_LIN
K=1
>
> 	  include-spirit
>
> 	:
<link>shared:<define>BOOST_SERIALIZATION_DYN_LIN
K=1
>
> 	;
>
> However I don't know the correct way to do it and I
couldn't find an
> example to copy from....

The feature you're looking for is "indirect conditional
requirement", 
documented at:

http://boost
.org/boost-build2/doc/html/bbv2/advanced/targets.html#bbv2.a
dvanced.targets.requirements

HTH,
Volodya
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