Concerns regarding some library functions

[Austin Clements]

Quoth David Bremner on Sep 27 at  1:59 pm:
> On Tue, 27 Sep 2011 16:25:58 +0300, Ali Polatel <polatel at gmail.com> wrote:
> 
> > The problem with their design is NULL return may both mean an error
> > condition and "message not found". However, we already have a similar
> > function which does not have such a flaw, namely notmuch_database_add_message().
> 
> So, I take there is no way to distinguish those two outcomes? That does
> sound bad. Looking at the code for notmuch-new, it looks like the return
> value of notmuch_database_find_message_by_filename is used without
> checking it for NULL.  Austin, can you comment on that at all?

I'd be happy to distinguish these outcomes.  I did
notmuch_database_find_message_by_filename the way I did only to be
consistent with notmuch_database_find_message.  Since ndfmbf isn't
entrenched yet, now is a good time to change it.

The call in notmuch-new should check the return, though if it can't
find the message at that point, something has gone terribly wrong.
Segfaulting is never the answer, though.