[RFC] 'bzr-email' using revision_id for threading

[Stephen J. Turnbull]

Robert Collins writes:

 > Perhaps a more interesting question then, is:
 > What will mail clients do with multiple messages with the same message-id.

Anything they please, because it's an error condition.  Behaviors I
have implemented include adding a command to my MUA to auto-prune
them, sending them to a generic killfiled-messages folder, sending
them to a special dupes folder, and sending them to /dev/null.

AFAIK, gmail for one automatically discards dupes.

 > > One way to think about it is that any text you personally add will be
 > > treated like those annoying prefixes before the body parts of a MIME
 > > message.
 > 
 > Well, commit messages can be dramatically different - 'st', full diffs,
 > semantic diffs, htmlised or not, etc. I'm not sure users will appreciate
 > the differences.

My point is that many users with capable mailers won't see them at
all, because messages with duplicate IDs will be hidden or discarded.

I think it would be good to provide an X-Bzr-Related-Revision-Ids
header with the broad definition "any revid you wanna put in there",
and let users with highly programmable MUAs find uses for it (this
includes not only Emacs-based MUAs and the like, but 'bots like the
Bundle Buggy).  If it turns out to be useful to have more specific
rules and interpretations for which revids you put in there, then
create new headers with appropriately restricted definitions.

I doubt that the use of Message-ID will correspond very well to the
threading behavior users will want from it, but we'll see.