bug#58531: 29.0.50; Wrong predicate used by map-elt gv getter

[Basil L. Contovounesios]

0. emacs -Q
1. M-x load-library RET map RET
2. (let ((l (list (cons 'a 1))))
     (setf (map-elt l "a" nil #'string=) 2)
     l)
   C-j

This correctly gives ((a . 2)).

3. (let ((l (list (cons 'a 1))))
     (cl-incf (map-elt l "a" nil #'string=))
     l)
   C-j

This gives the following backtrace:

Debugger entered--Lisp error: (wrong-type-argument number-or-marker-p nil)
  +(nil 1)
  (let* ((v (+ (map-elt l "a" nil) 1))) (condition-case nil (with-no-warnings 
(map-put! l "a" v #'string=)) (map-not-inplace (setq l (map-insert l "a" v)) 
v)))
  (let ((l (list (cons 'a 1)))) (let* ((v (+ (map-elt l "a" nil) 1))) 
(condition-case nil (with-no-warnings (map-put! l "a" v #'string=)) 
(map-not-inplace (setq l (map-insert l "a" v)) v))) l)
  (progn (let ((l (list (cons 'a 1)))) (let* ((v (+ (map-elt l "a" nil) 1))) 
(condition-case nil (with-no-warnings (map-put! l "a" v #'string=)) 
(map-not-inplace (setq l (map-insert l "a" v)) v))) l))
  eval((progn (let ((l (list (cons 'a 1)))) (let* ((v (+ (map-elt l "a" nil) 
1))) (condition-case nil (with-no-warnings (map-put! l "a" v #'string=)) 
(map-not-inplace (setq l (map-insert l "a" v)) v))) l)) t)
  elisp--eval-last-sexp(t)
  eval-last-sexp(t)
  eval-print-last-sexp(nil)
  funcall-interactively(eval-print-last-sexp nil)
  call-interactively(eval-print-last-sexp nil nil)
  command-execute(eval-print-last-sexp)

Whereas it should give the same result as step 2.
Patch to follow.

Thanks,

-- 
Basil

In GNU Emacs 29.0.50 (build 1, x86_64-pc-linux-gnu, X toolkit, cairo
 version 1.16.0, Xaw3d scroll bars) of 2022-10-14 built on tia
Repository revision: cbd04ad3d572850775f18bde868c71abcde733ed
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 11.0.12101004
System Description: Debian GNU/Linux bookworm/sid

Configured using:
 'configure 'CFLAGS=-Og -ggdb3' -C --prefix=/home/blc/.local
 --enable-checking=structs --with-file-notification=yes
 --with-x-toolkit=lucid --with-x'

Configured features:
ACL CAIRO DBUS FREETYPE GIF GLIB GMP GNUTLS GPM GSETTINGS HARFBUZZ JPEG
JSON LCMS2 LIBOTF LIBSELINUX LIBSYSTEMD LIBXML2 M17N_FLT MODULES NOTIFY
INOTIFY PDUMPER PNG RSVG SECCOMP SOUND SQLITE3 THREADS TIFF
TOOLKIT_SCROLL_BARS WEBP X11 XAW3D XDBE XIM XINPUT2 XPM LUCID ZLIB

Important settings:
  value of $LANG: en_IE.UTF-8
  value of $XMODIFIERS: @im=ibus
  locale-coding-system: utf-8-unix

Major mode: Debugger

Minor modes in effect:
  tooltip-mode: t
  global-eldoc-mode: t
  show-paren-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  tool-bar-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  buffer-read-only: t
  line-number-mode: t
  indent-tabs-mode: t
  transient-mark-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message mailcap yank-media puny dired
dired-loaddefs rfc822 mml mml-sec password-cache epa derived epg rfc6068
epg-config gnus-util text-property-search time-date subr-x mm-decode
mm-bodies mm-encode mail-parse rfc2231 mailabbrev gmm-utils mailheader
sendmail rfc2047 rfc2045 ietf-drums mm-util mail-prsvr mail-utils
help-fns radix-tree cl-print debug backtrace help-mode cl-macs map
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find-func rmc iso-transl tooltip eldoc paren electric uniquify
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term/common-win x-dnd tool-bar dnd fontset image regexp-opt fringe
tabulated-list replace newcomment text-mode lisp-mode prog-mode register
page tab-bar menu-bar rfn-eshadow isearch easymenu timer select
scroll-bar mouse jit-lock font-lock syntax font-core term/tty-colors
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korean japanese eucjp-ms cp51932 hebrew greek romanian slovak czech
european ethiopic indian cyrillic chinese composite emoji-zwj charscript
charprop case-table epa-hook jka-cmpr-hook help abbrev obarray oclosure
cl-preloaded button loaddefs faces cus-face macroexp files window
text-properties overlay sha1 md5 base64 format env code-pages mule
custom widget keymap hashtable-print-readable backquote threads dbusbind
inotify lcms2 dynamic-setting system-font-setting font-render-setting
cairo x-toolkit xinput2 x multi-tty make-network-process emacs)

Memory information:
((conses 16 51573 5638)
 (symbols 48 6489 0)
 (strings 32 18774 1872)
 (string-bytes 1 537756)
 (vectors 16 12706)
 (vector-slots 8 181823 10539)
 (floats 8 29 46)
 (intervals 56 370 2)
 (buffers 1000 11))