Allow programs to exclude files

However this works will need to allow for non-predictable locations (like .mozilla/firefox/al243lj3.defult/cache). Looking in some sort of user directory for these exclusion files is probably sufficient.

The non-predictable location problem can also be solved by simple wildcard support.

For wildcarding, I'd suggest file globbing patterns (as opposed to regular expressions). As I noted in a private email, I'd suggest that the patterns relative to $HOME be done in the traditional ~/foo style. This would mean you would ignore all patterns that did not start with "/" or "~".

Thinking about this more, it seems way better to just get apps to move to using the XDG cache dir. Either:

A) The app authors are willing to use the XDG spec.
B) The app authors are willing to add a deja-dup-specific exclusion file somewhere.
C) The app authors are willing to add some "standard" backup-program exlusion file somewhere.
D) The app authors aren't willing to consider this use case.

For A, we just win without effort.

For B & C, why not just use A instead? I don't think it would be worth the time and effort developing some syntax that had the support of multiple backup programs when XDG already did the work with wider backing. And I don't think Deja Dup is big enough that app authors would consider special support for it. Besides, by using the XDG spec, the app authors allow all sorts of programs to treat the files in special ways. Much more useful.

For D, we can't do anything anyway except build exclusions into Deja Dup if the use case is important enough (i.e. it affects a lot of uses and the app authors are unlikely to change -- something like Adobe Flash or some such).

So I'm going to mark this Won't Fix for now. If there are common cache-but-not-XDG-cache directories, separate bugs should be filed against Deja Dup to exclude them (as well as against the app itself to start using XDG).