Re: Fwd: Suggestion about derived files and commands

[Steven Knight]

> I'd like to use Cons to build our product. One drawback I can foresee
> right now is that we heavily use -DSOMETHING compilation option to
> choose some options of our software.
>
> In some cases, that may be a problem.
>
> Suppose that I have a compilation involving several hundred of C
> files.
>
> Then I build the product and test it.
>
> Then I discover a bug and I need to enable some instrumentation code
> in the product embedded in #ifdef LAB_TEST ... #ENDIF in 2 or 3 C
> files. To do this I'll add '-DLAB_TEST' in the CFLAGS variable used to
> create a new cons environment.
>
> So cons will recompile all c files to produce the object files since
> the compilation command has changed.
>
> That's fair enough since cons cannot parse the C files to know whether
> a derived file is affected by the -DLAB_TEST flag.
>
> But when I remove the -DLAB_TEST flag, cons will rebuild again all
> object files. That's may be quite long.

I think what you want is the UseCache feature, which already exists.  It
stores derived files in a directory using the build signature as the
name.  That way, when you go back and remove the -DLAB_TEST flag, all of
the previously-built files are already in the cache and just copied in
to your build tree whenever the signature matches.

Let me know if I misinterpreted what you're looking for.

        --SK