RE: [jamboost] FW: Conditional feature problem

From: Mark Elston (m.elston_at_[hidden])
Date: 2004-07-02 12:37:02

Thanks, Vladimir. It works now.

And thanks for the info as well. Just a couple more pieces of the puzzle
...

Mark

> -----Original Message-----
> From: Vladimir Prus [mailto:ghost_at_[hidden]]On Behalf Of Vladimir Prus
> Sent: Thursday, July 01, 2004 11:52 PM
> To: jamboost_at_[hidden]
> Subject: Re: [jamboost] FW: Conditional feature problem
>
>
> Mark Elston wrote:
> > Let me try this again.
>
> Oh, I'm sorry for missing your previous email. Was rather busy
> yesterday :-(
>
> > I have been trying to diagnose this by tracking down where these
> > values are set into the feature. The only place I can find is these
> > lines from builtin.jam:
> >
> > local os = [ modules.peek : OS ] ;
> > feature os : $(os) : propagated link-incompatible ;
> >
> > I can see from this why NT is the only allowed value and I get the
> > error I show below. However, I cannot see why the same Jamfile works
> > on Linux since it contains the <os>NT:... conditional property. It
> > looks like <os> is not a free feature but *may* only have the value
> > of the current OS.
>
> Yes, that's the case.
>
> > I also have not been able to track down what happens in the first
> > line above. The peek rule from modules.jam is:
> >
> > rule peek ( module-name ? : variables + )
> > {
> > module $(<)
> > {
> > return $($(>)) ;
> > }
> > }
>
> This code returns the value that 'variables' have in 'module-name'. The
>
> [ modules.peek : OS ]
>
> passes the empty module name, so values from the global module
> are returned.
>
> > >From the assignment to the 'os' variable above it looks like the peek
> >
> > is looking at the global OS variable, i.e. in no particular module.
> > Is that right? Where is this variable set? I have not been
> able to find
> > it in the jam files or in the jam_src directory.
>
> I believe it's set somewhere in jam_src: specifically in jam.h.
> For example,
> setting for NT is a line 93.
>
> > So I guess I have two questions:
> >
> > 1. Can I legitimately use conditional properties based on the
> <os> feature
> > in my Jamfiles?
>
> I think we need a small tweak here. The <toolset> feature can be used in
> condition without declaraing all the toolsets. I'll just disable
> validation
> for <os> as well, just like it's done for <toolset>. It's
> 'property.expand-subfeatures-in-conditions', if you're interested.
>
> And just to clarify the history. First we did not validate
> conditions at all,
> so <os>FOOBAR:<variant>release was OK even if FOOBAR was never
> known. Due to
> some other improvement in conditinal properties handling, we started
> validating conditions. This even caught some typos!
>
> But unfortunately, this problem <toolset>borland:<cxxflags>fooo
> -- it was now
> required that you have "using borland". So I've made <toolset> special --
> it's not validated when in condtion. I've just made <os>
> similiarly special.
> If you have build/property.jam revision 1.48, it should work.
>
> > 2. Just out of curiosity, what is the OS variable and how is it set?
>
> It's Jam variable which describes the platform Jam was built for.
> It's defined
> in "jam.h" and set in jam.c, line 359. Look for
>
> var_defines( othersyms );
>
> HTH,
> Volodya
>
>
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