[Scons-users] What affects rebuilding?

[Dirk Bächle]

Hi Douwe,

On 30.06.2015 17:04, Douwe Gelling wrote:
> I don't know specifics of scons, but it seems to me this isn't the issue. I've applied the patch to be certain, and it doesn't work
> in any case.
> It almost looks like the wrong files are compared when using variantdir, or perhaps some fields of the File object are being compared
> that shouldn't be. I'll have a look at the changed_since_last_build function, see what fields are compared.
>

your output messages from "--debug=explain" look a lot as if your actual files stay unchanged (equal hashsum), but the order in 
which they are found is different from run to run. This can happen when you have Builders like SWIG, or any custom Builder, which 
create headers or programs that are then used in the further build. In this way they are implicit dependencies and have to get 
checked on an update.
In the first run the created files don't exist initially, but in the second they do...so you get a different order in which files 
are found during the build phase.

Does your build keep quiet (no changes) when you run it a third time? Then you might also try to switch the implicit dependency 
detection for commands to "off", as described in 
http://stackoverflow.com/questions/11564403/how-do-i-tell-scons-to-ignore-implicit-dependencies-from-command-actions for example.

Hope this helps you a little further.

Best regards,

Dirk