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

[Basil L. Contovounesios]

"Basil L. Contovounesios" <contovob@tcd.ie> writes:

> Dmitry Gutov <dgutov@yandex.ru> writes:
>
>> 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
>
> LGTM.  Perhaps add a test as well:
>
> diff --git a/test/lisp/json-tests.el b/test/lisp/json-tests.el
> index 05837e83f9..9d7ffd5feb 100644
> --- a/test/lisp/json-tests.el
> +++ b/test/lisp/json-tests.el
> @@ -269,10 +269,13 @@ test-json-encode-plist-with-sort-predicate
>      (should (equal (json-encode plist) "{\"a\":1,\"b\":2,\"c\":3}"))))
>  
>  (ert-deftest test-json-encode-alist-with-sort-predicate ()
> -  (let ((alist '((:c . 3) (:a . 1) (:b . 2)))
> -        (json-encoding-object-sort-predicate 'string<)
> -        (json-encoding-pretty-print nil))
> -    (should (equal (json-encode alist) "{\"a\":1,\"b\":2,\"c\":3}"))))
> +  (let* ((alist '((:c . 3) (:a . 1) (:b . 2)))
> +         (clone (copy-sequence alist))
> +         (json-encoding-object-sort-predicate #'string<)
> +         (json-encoding-pretty-print nil))
> +    (should (equal (json-encode alist) "{\"a\":1,\"b\":2,\"c\":3}"))
> +    ;; Ensure sorting isn't destructive (bug#40693).
> +    (should (equal alist clone))))
>  
>  (ert-deftest test-json-encode-list ()
>    (let ((json-encoding-pretty-print nil))
>
>
> Eli, would this be okay for emacs-27?

Any chance of getting this fix in?

Thanks,

-- 
Basil