[Bf-committers] About linked IDs, make_local() and extern/indirect tags...

[Bastien Montagne]

Hey devs,

As you may have noticed (lol), I’ve been rampaging past days in some 
ID-management BKE areas (mostly, make_local one, but also copy to some 
extent), and I have a question about politics of id_lib_extern usage.

To summarize, when we make a datablock local, we have to tag all 
(linked) IDs it uses as 'extern' (and no more 'indirect') ones. So far, 
code mostly only tags 'refcounted' usages as extern (e.g. if you make an 
object local, all possible linked objects used as targets by its 
constraints/modifiers *will not* be tagged as 'extern' and will remain 
'indirect').

I cannot see any reason for this behavior, which only has a few 
exceptions like meshes' uvface/uvpoly images. To me it actually looks 
like a bug, since it means some non-refcounted usages may be lost at 
write/readfile time. Further more, there are some inconsistencies, e.g. 
BKE_camera_copy makes its dof_ob extern, while BKE_camera_make_local 
does not 'externalize' any pointer...

So question is: are you aware of any historical reason explaining that 
behavior? Is it still desired, or can we switch to a simple 
full-externalize callback here (for both copy and make_local funcs)?

Best regards,
Bastien

PS: I know the 'object targets of constraints/modifiers' in not a good 
example in practice, since objects are supposed to always be 
instantiated in scenes (i.e. always be 'extern' ones).