proposing "notmuch purge"

[Örjan Ekeberg]

While I like the idea of making it easy to prune away old junk messages
from the mail store, I find it dangerously disruptive to suddenly change
the semantics of the deleted tag.  To me, the deleted tag has always
meant something like "I do not want to see this message again; unless it
reappears in a thread or I explicitly search for it".  The possibility
to undelete also means that deleting messages is not such a big deal.

What do you think about introducing a new tag, e.g. purge, and let
"notmuch purge" destructively remove the messages with this tag set?
Hopefully, nobody is using that particular tag for a different purpose.

Purging would then become a two-stage process; first tagging which
messages should be purged, before doing the actual non-reversible
removal.  This makes it simpler to check what would be purged before
actually doing it.

A dangerous but flexible way of configuration would be to have a
pre-purge-hook which could, for example, do things like:

    notmuch tag +purge "(" tag:deleted OR tag:spam ")" AND date:..30days

The downside of this is of course that hooks are not that easy to set up
and can easily backfire and possibly remove your entire mail collection.

/Örjan