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

Bill Deegan bill at baddogconsulting.com
Thu Dec 29 12:50:51 EST 2016

As a workaround, perhaps add an action string which does nothing, but uses
the variables you depend on?
Just a thought.

Are the builders external python scripts which get run from the shell by
SCons? or are the builders python logic run inside scons?

On Thu, Dec 29, 2016 at 8:54 AM, Tom Tanner <trtanner at btinternet.com> wrote:

> 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.
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