I'm about to do my initial maildir import in to notmuch and I'm wondering
how people have dealt with the initial transition from maildir folders to
tags.  Many of my folders can be replaced by saved searches, but I would
like to convert the ones that don't make good searches into tags.

Ideally, notmuch would let me search by maildir folder, which would have the
added advantage of keeping things in sync going forward.  Unfortunately,
this looks difficult to support (possibly to the point of requiring a custom
query parser to do it efficiently).

I could extract all of the message ID's from the messages in these folders
and run a big notmuch tag command, but this sounds slow and potentially
error-prone.

Are there good solutions to this problem?