Improving BBv2 versioned toolsets

From: Michael Stevens (Michael.Stevens_at_[hidden])
Date: 2003-10-28 13:47:27

Dear All,

I have been looking at ways to improve the current way that toolset are 
versioned in BBv2. I have a lot of different compilers versions so this 
is important to me.

Firstly all the toolset definition have to work around the 'unspecified' 
default values problem. They all do this in a variety of complex ways.

Looking at the way toolsets have to handle this I think things could be 
significantly simplified if toolset versions were enforced. That is to 
say toolsets always were defined with the following init signiture.

rule init ( version : name ? : path ? )

For this to work the current way toolset build requests are invoked 
would have to change. Looking at the current code there is already 
special handling. The 'unspecifed' toolset is invoked specifically at 
line 157 of build-system.jam
for local t in $(targets)
{
local g = [ $(t).generate [ property-set.empty ] ] ;
virtual-targets += $(g[2-]) ;
}

It would be necessary to change this so the toolset is invoked with the 
first (or only) specified version. Sadly at this point in the code the 
trail goes cold for me. I'm unable to find where the 'unversioned' 
properties are generated by the special value 'property-set.empty'.

Enforcing versions would have a further significant side effect. With 
some toolsets it is currently possible to invoke the first definition 
both using the default 'unspecified' version and with a specified version.
Both invocations result in the same code (same property-set) but their 
target directories are named differently. This has often got me into 
trouble!

Hope this all make sense,
Michael