bug#70054: 30.0.50; Unknown ids in References: break threading

[Andrew Cohen <acohen@ust.hk>]

>>>>> "EZ" == Eli Zaretskii <eliz@gnu.org> writes:

[...]

    EZ> Ping!  Can we make some further progress with this bug report?

I worked with Jose to track everything down. This isn't a gnus bug and
the bug report can be closed.

Slightly more detail: the protonmail bridge adds non-existent ids to the
references header of messages (presumably used in some internal way by
the protonmail bridge). 'gnus is resilient in handling these: if
collecting threads by subject (the default) everything "just works". And
in case you (optionally) want to only use the references header for
threading, gnus has a way to alter the headers for exactly this
occasion: 'gnus-alter-header-function.  So the following:

(setq gnus-alter-header-function 'fix-protonmail-references)

(defun fix-protonmail-references (header)
  (setf (mail-header-references header)
        (mapconcat
         #'(lambda (x) (if (string-search "protonmail.internalid" x) "" x))
         (gnus-split-references (mail-header-references header)) " "))
  header)

will work.

I think this deserves to be in the gnus manual.  I have a commit in my local
tree to do this, which I will push to master.

-- 
Andrew Cohen