bug#40693: 28.0.50; json-encode-alist changes alist

[Dmitry Gutov]

Hi Ivan,

thanks for the report.

On 18.04.2020 05:59, Ivan Andrus wrote:
> It's late now, but if I have some time in the next few days, I may submit a 
> patch since it seems like a simple enough change.

How about this one?

diff --git a/lisp/json.el b/lisp/json.el
index 18d7fda882..b65884f913 100644
--- a/lisp/json.el
+++ b/lisp/json.el
@@ -564,9 +564,10 @@ json-encode-alist
   "Return a JSON representation of ALIST."
   (when json-encoding-object-sort-predicate
     (setq alist
-          (sort alist (lambda (a b)
-                        (funcall json-encoding-object-sort-predicate
-                                 (car a) (car b))))))
+          (sort (copy-sequence alist)
+                (lambda (a b)
+                  (funcall json-encoding-object-sort-predicate
+                           (car a) (car b))))))
   (format "{%s%s}"
           (json-join
            (json--with-indentation