This case was happening when a message had its own message ID in its
In-Reply-To header. The thread-resolution code would find the
partially constructed message, (with no thread ID yet), get garbage
from this function, and then march right along with that garbage.
With this commit, a self-cyclic message like this will now trigger an
internal error rather than marching along silienty. (And a subsequent
commit will remove the call to this function in this case.)
This function has only one caller, and that one caller was passing the
same value for both talloc_owner and the notmuch database. Dropping
the redundant argument simplifies the documentation of this function
considerably.
This reduces our reliance on open message_file objects, (so is a step
toward fixing the "too many open files" bug), but more importantly, it
means we don't load a self-referencing in-reply-to header, (since we
weed those out before adding any replyto terms to the database).
We now properly analyze the in-reply-to headers to create a proper
tree representing the actual thread and present the messages in this
correct thread order. Also, there's a new "depth:" value added to the
"message{" header so that clients can format the thread as desired,
(such as by indenting replies).
The existing notmuch_message_get_header is *almost* good enough for
this, except that we also need to remove the '<' and '>'
delimiters. We'll probably want to implement this function with
database storage in the future rather than loading the email message.
