Does gnus-summary-move-article need to clear the marks?

Does gnus-summary-move-article need to clear the marks?

[Kevin Boulain]

Hey,

I'm trying out Gnus and the IMAP server from which I'm getting my emails
is running a Sieve script that takes some actions, including setting a
bunch of IMAP keywords/flags ('client' ones, not the system ones like
\Seen as per https://www.rfc-editor.org/rfc/rfc3501#section-2.3.2).

When an email with these custom flags is marked as read (via 'd',
gnus-summary-mark-as-read-forward) and moved to another IMAP folder (via
'B m', gnus-summary-move-article) it loses its flags.

In the IMAP log (that I got with nnimap-record-commands) I can see:
  UID STORE 65 FLAGS.SILENT (\Seen)

A quick Edebug breakpoint on nnimap-request-set-mark (where the magic
seems to happen) gives the following backtrace:
  nnimap-request-set-mark("INBOX" (((65) set (read)) ((65) del (unexist seen forward unsend download cache save score dormant bookmark killed expire reply tick))) "$SERVER")
  gnus-request-set-mark("nnimap+$SERVER:INBOX" (((65) set (read)) ((65) del (unexist seen forward unsend download cache save score dormant bookmark killed expire reply tick))))
  gnus-summary-push-marks-to-backend(65)
  gnus-summary-move-article(nil)
  funcall-interactively(gnus-summary-move-article nil)
  command-execute(gnus-summary-move-article)

So the issue appears to be that gnus-summary-push-marks-to-backend calls
gnus-request-set-mark with 'set:
https://git.savannah.gnu.org/cgit/emacs.git/tree/lisp/gnus/gnus-sum.el?h=emacs-28.2#n10390

Should it be 'add instead, which should preserve the set of flags?
https://git.savannah.gnu.org/cgit/emacs.git/tree/lisp/gnus/nnimap.el?h=emacs-28.2#n1243

Similarly to what marking as read does:
  UID STORE 67 +FLAGS.SILENT (\Seen)
From around here:
https://git.savannah.gnu.org/cgit/emacs.git/tree/lisp/gnus/gnus-sum.el?h=emacs-28.2#n12896

This patch appears to work but I'm not familiar with the code:
diff --git i/lisp/gnus/gnus-sum.el w/lisp/gnus/gnus-sum.el
index 3f350bffb3..a13777cd95 100644
--- i/lisp/gnus/gnus-sum.el
+++ w/lisp/gnus/gnus-sum.el
@@ -10390 +10390 @@ ACTION can be either `move' (the default), `crosspost' or `copy'."
-    (gnus-request-set-mark gnus-newsgroup-name `(((,article) set ,set)
+    (gnus-request-set-mark gnus-newsgroup-name `(((,article) add ,set)

PS: I sent a similar email to ding@gnus.org a few days ago but it
doesn't look like it went through. Apologies if it ends up duplicated.