Date: Sun, 22 Jan 2012 13:16:09 -0500
From: Austin Clements <amdragon@MIT.EDU>
To: Mark Walters <markwalters1009@gmail.com>
Subject: Re: [PATCH] Automatically exclude tags in notmuch-show
Message-ID: <20120122181609.GQ16740@mit.edu>
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Quoth myself on Jan 20 at 12:18 pm:
> Quoth Mark Walters on Jan 20 at 12:10 am:
> > 
> > Ok Having said this is trivial I have found a problem. What should
> > notmuch do if you do something like
> > 
> > notmuch show id:<some-id>
> > and that message is marked with a deleted tag? To be consistent with the
> > other cases (where a deleted message is in a matched thread) we might
> > want to return the message with the not-matched flag set (eg in
> > JSON). But my patch doesn't, as it never even sees the thread since it
> > doesn't match.
> > 
> > Looking at notmuch-show.c I think we should not apply the exclude tags
> > to do_show_single, but usually should apply it to do_show. One solution
> > which is simple and is at least close to right would be to get do_show
> > to return the number of threads found. If this is zero then retry the
> > query without the excludes (possible setting the match_flag to zero on
> > each message since we know it does not match)
> > 
> > This is not a completely correct solution as if you ask notmuch-show to
> > show more than one thread it might  threads which only contain deleted
> > messages.
> > 
> > I can't see other good possibilities without slowing down the normal
> > path a lot (eg find all threads that match the original query and then
> > apply the argument above).
> > 
> > Any thoughts?
> 
> Oh dear.
> 
> Well, here's one idea.  Instead of doing a single thread query in
> show, do a thread query without the exclusions and then a message
> query with the exclusions.  Output all of the messages from the first
> query, but use the results of the second query to determine which
> messages are "matched".  The same could be accomplished in the library
> somewhat more efficiently, but it's not obvious to me what the API
> would be.

Here's a slightly crazier idea that's more library-invasive than the
original approach, but probably better in the long run.

Have notmuch_query_search_* return everything and make exclusion a
message flag like NOTMUCH_MESSAGE_FLAG_MATCH.  Tweak the definition of
"matched" to mean "matched and not excluded" (specifically, a message
would have the match flag or the excluded flag or neither, but not
both).  Search would skip threads with zero matched messages and I
think show would Just Work.

I can think of two ways to implement this.  notmuch_query_search_*
could perform both the original query and the query with exclusions
and use the docid set from the second to compute the "excluded"
message flag.  Alternatively, it could examine the tags of each
message directly to compute the flag.  The latter is probably easier
to implement, but probably slower.

Thoughts?