bug#74890: 31.0.50; (thing-at-point 'string) raises error

[Jean Louis <bugs@gnu.support>]

I can see that I cannot run (thing-at-point 'string) safely, though I
cannot exactly determine the condition.

In the buffer I have only this:

Hello

which is string "Hello" and when I place cursor behind "o" and run
(thing-at-point 'string) I am getting the backtrace below. But if I make
one space like "Hello " and place cursor on that empty space in the
buffer, I am getting NIL and no error.  Though I cannot repeat this with
emacs -Q and thus I do not know why is this happening exactly.

I think that  (eq (char-syntax (char-after)) 34) cannot read the char
which is not there "after".

Backtrace:

Debugger entered--Lisp error: (wrong-type-argument characterp nil)
  char-syntax(nil)
  (eq (char-syntax (char-after)) 34)
  (not (eq (char-syntax (char-after)) 34))
  (if (not (eq (char-syntax (char-after)) 34)) (setq syntax (syntax-ppss)) (or (progn (forward-char) (setq syntax (syntax-ppss)) (nth 3 syntax)) (progn (forward-char (- (or nil 1))) (setq syntax (syntax-ppss)) (nth 3 syntax))))
  (let (syntax beg end) (if (not (eq (char-syntax (char-after)) 34)) (setq syntax (syntax-ppss)) (or (progn (forward-char) (setq syntax (syntax-ppss)) (nth 3 syntax)) (progn (forward-char (- (or nil 1))) (setq syntax (syntax-ppss)) (nth 3 syntax)))) (and (nth 3 syntax) (condition-case nil (progn (setq beg (nth 8 syntax)) (setq end (progn (goto-char (nth 8 syntax)) (forward-sexp) (point)))) (error nil)) (cons beg end)))
  (save-excursion (let (syntax beg end) (if (not (eq (char-syntax (char-after)) 34)) (setq syntax (syntax-ppss)) (or (progn (forward-char) (setq syntax (syntax-ppss)) (nth 3 syntax)) (progn (forward-char (- (or nil 1))) (setq syntax (syntax-ppss)) (nth 3 syntax)))) (and (nth 3 syntax) (condition-case nil (progn (setq beg (nth 8 syntax)) (setq end (progn (goto-char ...) (forward-sexp) (point)))) (error nil)) (cons beg end))))
  tap-bounds-of-string-at-point()
  (let ((bounds (tap-bounds-of-string-at-point))) (and bounds (buffer-substring (car bounds) (cdr bounds))))
  tap-string-at-point()
  funcall(tap-string-at-point)
  (prog1 (funcall thing-fn) (constrain-to-field nil opoint))
  (let* ((opoint (point)) (thg (prog1 (funcall thing-fn) (constrain-to-field nil opoint)))) thg)
  (if thing-fn (let* ((opoint (point)) (thg (prog1 (funcall thing-fn) (constrain-to-field nil opoint)))) thg) (let ((bounds (tap-bounds-of-thing-at-point thing syntax-table))) (and bounds (buffer-substring (car bounds) (cdr bounds)))))
  (let* ((thing-fn (or (get thing 'tap-thing-at-point) (get thing 'thing-at-point))) (something (if thing-fn (let* ((opoint (point)) (thg (prog1 ... ...))) thg) (let ((bounds (tap-bounds-of-thing-at-point thing syntax-table))) (and bounds (buffer-substring (car bounds) (cdr bounds))))))) (if (and (stringp something) no-properties) (progn (set-text-properties 0 (length something) nil something))) something)
  thing-at-point(string)
  eval((thing-at-point 'string) t)
  #f(compiled-function () #<bytecode 0x15ba1ac9559f7d5d>)()
  #f(compiled-function () #<bytecode -0x5db3e1955cb81d1>)()
  eval-expression((thing-at-point 'string) nil nil 127)
  funcall-interactively(eval-expression (thing-at-point 'string) nil nil 127)
  command-execute(eval-expression)



In GNU Emacs 31.0.50 (build 4, x86_64-pc-linux-gnu, GTK+ Version
 3.24.38, cairo version 1.16.0) of 2024-12-05 built on lco2
Repository revision: 25b4bf7fcd75564f23b2e60e29e8ff7354186371
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 11.0.12101007
System Description: Debian GNU/Linux 12 (bookworm)

Configured using:
 'configure --with-mailutils --with-native-compilation=yes
 --with-tree-sitter --with-imagemagick'

Configured features:
ACL CAIRO DBUS FREETYPE GIF GLIB GMP GNUTLS GSETTINGS HARFBUZZ
IMAGEMAGICK JPEG LCMS2 LIBSELINUX LIBXML2 MODULES NATIVE_COMP NOTIFY
INOTIFY PDUMPER PNG RSVG SECCOMP SOUND SQLITE3 THREADS TIFF
TOOLKIT_SCROLL_BARS TREE_SITTER WEBP X11 XDBE XIM XINPUT2 XPM GTK3 ZLIB

Important settings:
  value of $LC_ALL: en_US.UTF-8
  value of $LANG: de_DE.UTF-8
  value of $XMODIFIERS: @im=exwm-xim
  locale-coding-system: utf-8-unix

Major mode: Lisp Interaction

Minor modes in effect:
  tooltip-mode: t
  global-eldoc-mode: t
  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
  minibuffer-regexp-mode: 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
cl-loaddefs cl-lib sendmail rfc2047 rfc2045 ietf-drums mm-util
mail-prsvr mail-utils rmc iso-transl tooltip cconv eldoc paren electric
uniquify ediff-hook vc-hooks lisp-float-type elisp-mode mwheel
term/x-win x-win term/common-win x-dnd touch-screen 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 frame minibuffer nadvice seq simple cl-generic
indonesian philippine cham georgian utf-8-lang misc-lang vietnamese
tibetan thai tai-viet lao 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
theme-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 gtk
x-toolkit xinput2 x multi-tty move-toolbar make-network-process
native-compile emacs)

Memory information:
((conses 16 49894 11144) (symbols 48 5434 0) (strings 32 14122 1285)
 (string-bytes 1 414224) (vectors 16 9179)
 (vector-slots 8 129869 10829) (floats 8 22 2) (intervals 56 247 8)
 (buffers 992 11))

-- 
Jean