Avoiding unneccessary updates due to Jamfile modifications

From: David Abrahams (david.abrahams_at_[hidden])
Date: 2001-11-22 11:08:26

Ulli's recent ideas about generating Jam-readable configuration files (see
the wiki:
http://www.crystalclearsoftware.com/cgi-bin/boost_wiki/wiki.pl?Configuration
_And_Installation) got me thinking about the plans to make all targets
dependent on the Jamfiles which declare them. Of course that's probably OK
in the short term, but it would cause many things to be rebuilt when there
was no need. I think we can do much better: all we need to do is write a
Jam-readable file that contains the neccessary information (command-line
parameters, usually) about each target, and compare that information with
the information generated by each new build request. If there is a change,
we can use the ALWAYS rule to cause the target to be updated. That way, the
target will be updated if any of its dependencies change, and also if the
information used to build it changes.

-Dave