Revert "Obsolete local set difference functions in favor of seq-difference"

This reverts commit 20f7fa691b7c2859b96550d9ccb326bf394e160d.

gnus-set-difference is orders of magnitude faster than seq-difference
(on these sets), and using seq-difference makes nnimap too
slow.

1 files changed, 11 insertions, 3 deletions

diff --git a/lisp/gnus/spam.el b/lisp/gnus/spam.el
index 3f978918b9a..d00f0a60b66 100644
--- a/lisp/gnus/spam.el
+++ b/lisp/gnus/spam.el
@@ -710,8 +710,16 @@ finds ham or spam.")
 (defun spam-set-difference (list1 list2)
   "Return a set difference of LIST1 and LIST2.
 When either list is nil, the other is returned."
-  (declare (obsolete seq-difference "28.1"))
-  (seq-difference list1 list2 #'eq))
+  (if (and list1 list2)
+      ;; we have two non-nil lists
+      (progn
+        (dolist (item (append list1 list2))
+          (when (and (memq item list1) (memq item list2))
+            (setq list1 (delq item list1))
+            (setq list2 (delq item list2))))
+        (append list1 list2))
+    ;; if either of the lists was nil, return the other one
+    (if list1 list1 list2)))
 
 (defun spam-group-ham-mark-p (group mark &optional spam)
   "Checks if MARK is considered a ham mark in GROUP."
@@ -1319,7 +1327,7 @@ In the case of mover backends, checks the setting of
              (new-articles (spam-list-articles
                             gnus-newsgroup-articles
                             classification))
-             (changed-articles (seq-difference new-articles old-articles #'eq)))
+             (changed-articles (spam-set-difference new-articles old-articles)))
         ;; now that we have the changed articles, we go through the processors
         (dolist (backend (spam-backend-list))
           (let (unregister-list)