master 61f8f7f68f: cl-generic.el: Fix bug#46722

[Stefan Monnier]

branch: master
commit 61f8f7f68f3bac5dc7ab41532902c480417552d8
Author: Stefan Monnier <monnier@iro.umontreal.ca>
Commit: Stefan Monnier <monnier@iro.umontreal.ca>

    cl-generic.el: Fix bug#46722
    
    Fix longstanding bug due to unexpected interference via side-effect.
    
    * lisp/emacs-lisp/cl-generic.el (cl--generic-get-dispatcher):
    Copy the `dispatch` arg before storing it into the hash-table.
---
 lisp/emacs-lisp/cl-generic.el | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/lisp/emacs-lisp/cl-generic.el b/lisp/emacs-lisp/cl-generic.el
index 983694204d..5090e06037 100644
--- a/lisp/emacs-lisp/cl-generic.el
+++ b/lisp/emacs-lisp/cl-generic.el
@@ -604,7 +604,9 @@ The set of acceptable TYPEs (also called \"specializers\") 
is defined
 
 (defun cl--generic-get-dispatcher (dispatch)
   (with-memoization
-      (gethash dispatch cl--generic-dispatchers)
+      ;; We need `copy-sequence` here because this `dispatch' object might be
+      ;; modified by side-effect in `cl-generic-define-method' (bug#46722).
+      (gethash (copy-sequence dispatch) cl--generic-dispatchers)
     ;; (message "cl--generic-get-dispatcher (%S)" dispatch)
     (let* ((dispatch-arg (car dispatch))
            (generalizers (cdr dispatch))