Re: Creating build version numbers (was RE: How to always build a tar get?)

[Steven Knight]

On Mon, 30 Oct 2000, Eric Brown wrote:
> > Invoking something every time and letting the underlying tool handle part
> > of the dependency analysis runs counter to Cons' design.  Cons would
> > have no way of knowing that your smart tool figured out that it didn't
> > need to update the header file.  Hence, Cons would still think the header
> > file had been rebuilt every time, and it would then try to rebuild every
> > target that depends on that header file every time, which is probably not
> > what you want.  You could get around this by Ignore()ing the dependency
> > on the header file, but then the dependent targets wouldn't get rebuilt
> > when you actually wanted them to...
> 
> OK.  What I really want is the header in question (which contains a build
> version number) to get rebuilt on the first build of the day (and not
> thereafter).  Is there a good (or even feasible) way to do this?

Heck, why not do it in straight Perl?  (The light bulb just came on...)
Since you already have a tool to do this, you could just call system to
do it:

        system("tool_to_update_version_number version_file.h");

That way, Cons would be happy because it would simply detect the change
to the contents of the version file and rebuild anything that includes
it as appropriate.

This would work because it keeps the separate "dependency" calculation
(based on whether this is the first build of the day) outside of the Cons
dependency tree.  The problem with trying to "build" the file every time
through a Cons method like Command is that it mixes the two different
dependency mechanisms, with unfortunate side effects...

        --SK