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

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

[Jean Louis]

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

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

[Jean Louis]

Now I realized that this bug is related to Drew's thingatpt+ as when I turned it off, the bug did not appear again.

Drew, do you maybe know how to improve this?

Jean Louis

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

[Eli Zaretskii]

> From: Jean Louis <bugs@gnu.support>
> Date: Sun, 15 Dec 2024 11:27:24 +0300
> 
> 
> 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)

Please show a complete recipe, preferably starting from "emacs -Q".  I
tried to reproduce this problem, but couldn't, which probably means
some special steps are required to see it.

I also don't understand your claims about "char after", because
there's always something "after" point.

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

[Stefan Kangas]

Jean Louis <bugs@gnu.support> writes:

> Now I realized that this bug is related to Drew's thingatpt+ as when I
> turned it off, the bug did not appear again.

Thanks, since this bug is not about Emacs, I'm closing it now.

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

[Jean Louis]

* Eli Zaretskii <eliz@gnu.org> [2024-12-15 21:32]:
> > Debugger entered--Lisp error: (wrong-type-argument characterp nil)
> >   char-syntax(nil)
> >   (eq (char-syntax (char-after)) 34)
> 
> Please show a complete recipe, preferably starting from "emacs -Q".  I
> tried to reproduce this problem, but couldn't, which probably means
> some special steps are required to see it.
> 
> I also don't understand your claims about "char after", because
> there's always something "after" point.

When I removed loading of Drew's thingatpt+ I could not observe this problem anymore.

I just think it is related to function from that library `tap-bounds-of-string-at-point'

Jean

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

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

> > > Debugger entered--Lisp error: (wrong-type-argument characterp nil)
> > >   char-syntax(nil)
> > >   (eq (char-syntax (char-after)) 34)
> >
> > Please show a complete recipe, preferably starting from "emacs -Q".  I
> > tried to reproduce this problem, but couldn't, which probably means
> > some special steps are required to see it.
> >
> > I also don't understand your claims about "char after", because
> > there's always something "after" point.

No, there's _not_ always something (some text) after
point.  And that, I think, is what this report is about.
From Jean's description, the only text in the buffer is
`Hello', where that `o' char is the last char, and
point is _after_, not on/at, that `o'.

> When I removed loading of Drew's thingatpt+ I could not observe this
> problem anymore.
> 
> I just think it is related to function from that library `tap-bounds-of-
> string-at-point'

Hi Jean,

I see the same thing with `emacs -Q' for Emacs 29.4,
which is the latest Emacs release AFAIK:

Debugger entered--Lisp error: (wrong-type-argument characterp nil)
  thing-at-point-bounds-of-string-at-point()
  bounds-of-thing-at-point(string)
  thing-at-point(string)
  eval-expression((thing-at-point 'string) nil nil 127)
  funcall-interactively(eval-expression (thing-at-point 'string) nil nil 127)
  command-execute(eval-expression)

To me, this behavior makes sense since, per your recipe,
there's _no character_ at point, and for thing-at-point
to tell whether or not _the buffer text at point_
represents a given type of thing or not there must at
least be a char at point!

(You'll get the same error if you try thing-at-point
in an empty buffer - no char at point to test.  I see
that too with Emacs 29.4.)

An alternative behavior - incorrect/poorer IMO - could
conceivably be to return nil.  But to me (and to vanilla
Emacs -Q for all releases I know of), that would be
claiming that _there's text at point_ that does not
represent such a thing.

Your Emacs bug #74890 says you're using an Emacs 31
development version.  Emacs 30 hasn't even been released
yet!  The bleeding edge bleeds, and I'm hoping Emacs 31's
current failure to raise an error in this context is an
ephemeral bug that'll be fixed before release.  (This is a
regression - a backward-incompatible change.  But it may
be intentional.)

If _released_ Emacs 31 thing-at-point changes the behavior
to instead return nil, then I'll have to decide whether to
follow suit.  My feeling, for now at least, is that that's
poor behavior (a bug).  And if I go with that feeling then
at most I'll perhaps provide an option to give users such
(misguided) behavior if they so choose.

To me, it's important that thing-at-point be usable _not_
just to grab some text at point to use as a default value
but - more importantly, if less commonly - to test whether
there's a given type of thing at point, i.e., for
_conditional/filtering_ behavior.  With such an outlook I
think it's important for the testing to be doable and done
on (duh!) text, i.e., a character at point.

That such filtering behavior is important to me is also
why my code returns nil when just _after_ a thing (not
on/at a thing).

One day, vanilla Emacs opted to return a thing that's just
before, not at point.  I disagreed with that change when
it was made, but was overruled.  I think it's due to a
shortsighted opinion that the only use for thing-at-point
is to grab some text for use as a default value - not _at_
point, but _near_ point.  For that use case thingatpt+.el
provides different functions: *-near[est]-point.  Those
functions let you specify what you mean by "near".

When you can repro the bug with `thingatpt+.el', but not
`emacs -Q', in an actual Emacs release (e.g. 31), please
send me a mail with a recipe to repro it.  Thx.