Re: [Boost-build] eval default property fails

Subject: Re: [Boost-build] eval default property fails
From: Vladimir Prus (ghost_at_[hidden])
Date: 2010-11-13 03:08:40

On Saturday, November 13, 2010 10:06:59 Oliver Kowalke wrote:
> Hi,
> in my Jamfile I add a new property/feature called 'abi' which should get
> an default value (calculated by 'default_abi()'):
> 
> local rule eval_architecture ( properties * )
> {
> 	local result = "" ;
> ...
> 	return $(result) ;
> }
> 
> local rule default_abi ( properties * )
> {
> 	local result = sysv ;
> 	local arch = [ eval_architecture $(properties) ] ;
> 
>          if <target-os>windows in $(properties) { result = ms ; }
> 	else if $(arch) = "arm" { result = aapcs ; }
> 	return $(result) ;
> }
> 
> feature.feature abi
> 
>     : aapcs
> 
> 	 eabi
> 	 ms
> 	 n32
> 	 n64
> 	 o32
> 	 o64
>       sysv
> 
>     : propagated
> 
>     ;
> feature.set-default abi : [ default_abi $(properties) ] ;
> 
> The problem is, that 'local arch = [ eval_architecture $(properties) ]'
> in 'default_abi()' does not evaluate 'properties'. It seams that
> 'properties' contains nothing.

Yes, indeed, because there's no such variable in the scope of Jamfile, unless 
you have defined such variable yourself.

> How do I have to pass 'properties' to 'default_abi()' invoked in
> 'feature.set-default abi' so that 'eval_architecture()' can inspect the
> builtin-proprties like <archtiecture>, <instructions-set>, <target-os> etc.

Please understand that each Jamfile is read exactly once. Further, the default 
value of a feature is set globally for a given Boost.Build run, while a given
metatarget can be generated many times, with different values of
<architecture> and <target-os> and what not. Therefore, it's not
possible to set default value of a feature like that.

I suggest you use indirect conditional requirements for your purposes
(documented in the manual), so that the value of 'abi' is defaulted
appropriately to the build properties.

- Volodya

-- 
Vladimir Prus
http://vladimir_prus.blogspot.com
Boost.Build: http://boost.org/boost-build2