[Scons-users] env[X'] and signatures

[Tom Tanner]

On 27/12/16 18:22, Bill Deegan wrote:
> If every builder depends on all values in env['ENV'], then any change 
> will rebuild everything.
> This is almost never warranted.

But then why does scons clear out the supplied environment? It is 
precisely because everything behaves in a way that is unclear and not 
reproducable if you don't know exactly what the environment is.
> I think, ideally, a builder (Action really), would specify what parts 
> of the Environment() it's sensitive too.

This would be better. If every builder specified which parts of 
env['ENV'] it is interested in, and they (and nothing else) got passed 
through and added to the build signature

>
> Remember, while many users are only building source code which is 
> fairly quick, SCons is used in other "build" systems where steps can 
> take considerable time and resources so extraneous rebuilds are quite 
> costly for them.
>
> -Bill

I agree but specifying the correct dependencies are how you avoid costly 
rebuilds. Not rebuilding something that has changed can be just as 
costly because instead of finding out about it at the build stage, you 
find out about it when it is on a production machine.