GNU bug report logs - #70524
[PATCH] Fix `map-elt` with `setf` for subplaces

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From: Augusto Stoffel <arstoffel <at> gmail.com>
To: 70524 <at> debbugs.gnu.org
Cc: michael_heerdegen <at> web.de, okamsn <at> protonmail.com, monnier <at> iro.umontreal.ca
Subject: bug#70524: [PATCH] Fix `map-elt` with `setf` for subplaces
Date: Thu, 25 Apr 2024 14:03:47 +0200

On Tue, 23 Apr 2024 at 02:10, Okamsn via "Bug reports for GNU Emacs, the Swiss army knife of text editors" wrote:

> Hello,
>
> Currently, the use
>
>      (let ((arr (vector 0 1 2 3 4 5 6)))
>        (setf (map-elt (cl-subseq arr 3) 0)
>              27)
>        arr)
>
> expands to
>
>      (let ((arr (vector 0 1 2 3 4 5 6)))
>        (let* ((v arr))
>          (condition-case nil
>              (with-no-warnings
>                (map-put! (cl-subseq v 3) 0 27 nil))
>            (map-not-inplace
>             (let* ((new (map-insert (cl-subseq v 3) 0 27)))
>               (progn
>                 (cl-replace v new :start1 3 :end1 nil)
>                 new))
>             27)))
>        arr)

Since map-put! may raise a not-in-place signal, and I doubt the macro
expansion checks for whatever condition it is that leads to that, I
would say this use-case is essentially broken.

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