From: Aaron Ecay <aaronecay@gmail.com>
To: Jani Nikula <jani@nikula.org>, notmuch@notmuchmail.org
Subject: Re: [RFC] [PATCH] lib/database.cc: change how the parent of a message
	is calculated
In-Reply-To: <871ubzt5gr.fsf@nikula.org>
References: <1361836225-17279-1-git-send-email-aaronecay@gmail.com>
	<87621cteeb.fsf@nikula.org> <871ubzt5gr.fsf@nikula.org>
User-Agent: Notmuch/0.15.2+33~g0c0a530 (http://notmuchmail.org)
	Emacs/24.3.50.2 (x86_64-unknown-linux-gnu)
Date: Sun, 03 Mar 2013 18:46:18 -0500
Message-ID: <87wqtovygl.fsf@gmail.com>
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Precedence: list

Hi Jani,

Thanks to you and Austin for the comments.

2013ko martxoak 1an, Jani Nikula-ek idatzi zuen:
>> I think the background is that RFC 822 defines In-Reply-To (and
>> References too for that matter) as *(phrase / msg-id), while RFC 2822
>> defines them as 1*msg-id. I'd like something about RFC 822 being
>> mentioned in the commit message.
>>=20
>> The problem in the gmane message you link to in
>> id:87liaa3luc.fsf@gmail.com is likely related to the FAQ item 05.26
>> "How do I fix a bogus In-Reply-To or missing References field?" in
>> the MH FAQ http://www.newt.com/faq/mh.html.

Likely yes.  But I think notmuch should handle these messages, since
they are seen in the wild (and I don=E2=80=99t think you disagree with me on
this point?)


>>=20
>> As the comment for the function says, we explicitly avoid including
>> self-references. I think I'd err on the safe side and return NULL if
>> the last ref equals message-id.

Done.

>>=20
>> I don't know how you got this non-change hunk here, but please remove
>> it. :)

That=E2=80=99s what I get for setting my editor to delete trailing whitespa=
ce on
save (then not reading outgoing patches carefully).  Fixed.

>> I wonder if you should reuse your parse_references() change here, so
>> you'd set in_reply_to_message_id to the last message-id in
>> In-Reply-To. This might tackle some of the problematic cases
>> directly, but should still be all right per RFC 2822. I didn't verify
>> how the parser handles an RFC 2822 violating free form header though.
>=20
> Strike that based on http://www.jwz.org/doc/threading.html:
>=20
> "If there are multiple things in In-Reply-To that look like
> Message-IDs, only use the first one of them: odds are that the later
> ones are actually email addresses, not IDs."

Hmm.  I think it=E2=80=99s a toss-up which of multiple quasi-message-ids is=
 the
real one.  In the email message example I linked upthread, it was the
last one that was real.  I decided to use the last one, because it
allows the self-reference checking to be pushed entirely into
parse_references.  If you feel strongly that we should use the first
one, I can change it back.

> I talked to Austin (CC) about the patch on IRC, and his comment was,
> perceptive as always:
>=20
>  23:38 amdragon Is the logic in that patch equivalent to always using
> the last message ID in references unless there is no references
> header?  Seems like it is, but in a convoluted way.
>=20
> And that's actually the case, isn't it? To make the code reflect that,
> you should use last_ref_message_id, and if that's NULL, fallback to
> in_reply_to_message_id.

Yes.  Fixed.

>=20
>> I suggest adding an else if branch (or revamp the above if condition)
>> to tackle the missing In-Reply-To header:
>>=20
>> else if (!in_reply_to_message_id && last_ref_message_id) {
>> in_reply_to_message_id =3D last_ref_message_id; }
>=20
> Strike that, it should be the other way round.

Now that the self-reference check is in parse_references, the
conditional is much simpler.

One additional change I made in this version was to factor out 3 calls
to =E2=80=9Cnotmuch_message_get_message_id (message)=E2=80=9D into a variab=
le inside the
_notmuch_database_link_message_to_parents function, for a small boost to
readability (and perhaps speed, depending on how clever the compiler is
I guess).

I also added tests =E2=80=93 those are the first of two patches that will f=
ollow
this email, the second being the code to make them pass.

--=20
Aaron Ecay