[Boost-build] Method for expressing complex requirements logic

From: Vladimir Prus (ghost_at_[hidden])
Date: 2006-01-28 09:58:54

Hi!
Some of the Boost libraries have pretty contrived logic in their regression 
tests. So example, if the toolset is borland, the serialization library will 
check for global variable SPIRIT_ROOT, and if that's set, add its value to 
<include>, and if it's not set, error out.

In V1 this is accomplished by adding a name of a rule to requirements, which 
rule will be called to compute extra requirements.

The question is how to best implement this in V2. I've outlined three posible 
methods in 

   https://zigzag.cs.msu.su:7813/boost.build/ticket/23

Anybody can comment which one seems best?

- Volodya