bug#50290: Using `setf` on `map-elt` repeats evaluation for returning the value of `setf`

bug#50290: Using `setf` on `map-elt` repeats evaluation for returning the value of `setf`

[Okamsn via Bug reports for GNU Emacs, the Swiss army knife of text editors]

Hello,

When I do `(setf (map-elt map key) (my-func))`, it expands to

     (let* ((key key))
       (condition-case nil
           (with-no-warnings
             (map-put! map key (my-func) nil))
         (map-not-inplace
          (setq map (map-insert map key (my-func)))
          (my-func))))

The repetition of `(my-func)` raises warnings.  Compare with using
`(setf (alist-get key map) (my-func))`, where the result of `(my-func)`
is bound to `v` so that it is only called once:

     (let* ((p (if (and nil (not (eq nil 'eq)))
                   (assoc key map nil)
                 (assq key map)))
            (v (my-func)))
       (progn
         (if p
             (setcdr p v)
           (setq map (cons (setq p (cons key v))
                           map)))
         v))

This is on Emacs 28 with Map.el 3.1.

bug#50290: Using `setf` on `map-elt` repeats evaluation for returning the value of `setf`

[Lars Ingebrigtsen]

Okamsn <okamsn@protonmail.com> writes:

> When I do `(setf (map-elt map key) (my-func))`, it expands to
>
>      (let* ((key key))
>        (condition-case nil
>            (with-no-warnings
>              (map-put! map key (my-func) nil))
>          (map-not-inplace
>           (setq map (map-insert map key (my-func)))
>           (my-func))))
>
> The repetition of `(my-func)` raises warnings. 

Yup.  This should now be fixed on the trunk.

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no