bug#52097: 28.0.50; Regression - posn-at-point returns wrong result if overlay is present

bug#52097: 28.0.50; Regression - posn-at-point returns wrong result if overlay is present

[Daniel Mendler]

1. emacs -Q
2. Create new buffer bug.el
3. Activate flymake-mode (for the overlay)
4. Enter "  invalid-ident" (note the spaces at the beginning)
5. Wait until the flymake overlay appears

6a. Move the point to the buffer beginning
7a. M-: (posn-x-y (posn-at-point)) -> (0 . 0) is reported, correct

6b. Move the point to the beginning of "|invalid-ident" with the overlay
7b. M-: (posn-x-y (posn-at-point)) -> (26 . 21) is reported, Y wrong

6c. Move the point to the right, "i|nvalid-ident"
7c. M-: (posn-x-y (posn-at-point)) -> (39 . 0) is reported, correct

This bug is a regression of Emacs 28. I cannot reproduce this on Emacs
27, there I always get Y=0.

In GNU Emacs 28.0.50 (build 58, x86_64-pc-linux-gnu, GTK+ Version
3.24.5, cairo version 1.16.0)
 of 2021-08-13 built on projects
Repository revision: 30ca42b49d5b5316abb3ebad38b0e9629eb52920
Repository branch: deferred-highlighting-version2
Windowing system distributor 'The X.Org Foundation', version 11.0.12004000
System Description: Debian GNU/Linux 10 (buster)

Configured using:
 'configure --prefix=/home/user/emacs/install --with-cairo'

Configured features:
CAIRO DBUS FREETYPE GIF GLIB GMP GNUTLS GSETTINGS HARFBUZZ JPEG
LIBSELINUX LIBXML2 MODULES NOTIFY INOTIFY PDUMPER PNG SECCOMP SOUND
THREADS TIFF TOOLKIT_SCROLL_BARS X11 XDBE XIM XPM GTK3 ZLIB

Important settings:
  value of $LANG: en_US.UTF-8
  locale-coding-system: utf-8-unix

Major mode: Message

Minor modes in effect:
  mml-mode: t
  tooltip-mode: t
  global-eldoc-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
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  line-number-mode: t
  auto-fill-function: message-do-auto-fill
  transient-mark-mode: t
  abbrev-mode: t

Load-path shadows:
None found.

Features:
(kmacro pp shadow sort mail-extr emacsbug message rmc puny dired
dired-loaddefs rfc822 mml mml-sec epa derived epg epg-config gnus-util
rmail rmail-loaddefs auth-source eieio eieio-core eieio-loaddefs
password-cache json map mm-decode mm-bodies mm-encode mail-parse rfc2231
mailabbrev gmm-utils mailheader sendmail rfc2047 rfc2045 ietf-drums
mm-util mail-prsvr mail-utils cl-extra time-date subr-x autoload
radix-tree checkdoc lisp-mnt help-mode cl-macs cl-seq flymake-proc
flymake compile text-property-search comint ansi-color ring warnings
thingatpt vc-git diff-mode easy-mmode vc-dispatcher cl-loaddefs cl-lib
bug-reference seq byte-opt gv bytecomp byte-compile cconv two-column
iso-transl tooltip eldoc electric uniquify ediff-hook vc-hooks
lisp-float-type mwheel term/x-win x-win term/common-win x-dnd tool-bar
dnd fontset image regexp-opt fringe tabulated-list replace newcomment
text-mode elisp-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 cl-generic
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 charscript charprop
case-table epa-hook jka-cmpr-hook help simple abbrev obarray
cl-preloaded nadvice button loaddefs faces cus-face macroexp files
window text-properties overlay sha1 md5 base64 format env code-pages
mule custom widget hashtable-print-readable backquote threads dbusbind
inotify dynamic-setting system-font-setting font-render-setting cairo
move-toolbar gtk x-toolkit x multi-tty make-network-process emacs)

Memory information:
((conses 16 71359 11512)
 (symbols 48 8479 2)
 (strings 32 24937 1971)
 (string-bytes 1 821235)
 (vectors 16 16877)
 (vector-slots 8 214845 16955)
 (floats 8 40 25)
 (intervals 56 530 0)
 (buffers 992 18))

bug#52097: 28.0.50; Regression - posn-at-point returns wrong result if overlay is present

[Eli Zaretskii]

> From: Daniel Mendler <mail@daniel-mendler.de>
> Date: Thu, 25 Nov 2021 11:13:04 +0100
> 
> 1. emacs -Q
> 2. Create new buffer bug.el
> 3. Activate flymake-mode (for the overlay)
> 4. Enter "  invalid-ident" (note the spaces at the beginning)
> 5. Wait until the flymake overlay appears

The overlay doesn't seem to appear for me, for some reason.

Could you please post a recipe that doesn't require Flymake?  Surely,
creating an overlay doesn't require such heavy machinery?  I tried to
put a simple overlay with before-string in a buffer, but didn't see
any problem with the Y coordinate reported by posn-at-point, so I
guess there's a need in something special in that overlay.

Thanks.

bug#52097: 28.0.50; Regression - posn-at-point returns wrong result if overlay is present

[Daniel Mendler]

>> 1. emacs -Q
>> 2. Create new buffer bug.el
>> 3. Activate flymake-mode (for the overlay)
>> 4. Enter "  invalid-ident" (note the spaces at the beginning)
>> 5. Wait until the flymake overlay appears
> 
> The overlay doesn't seem to appear for me, for some reason.

I am using emacs -Q. I just recompiled the current emacs-28 branch.
After some time flymake should underline the invalid identifier.

> Could you please post a recipe that doesn't require Flymake?
Try this command:

(defun posn-bug ()
  (interactive)
  (let ((buffer (get-buffer-create "*bug*")))
    (with-current-buffer buffer
      (erase-buffer)
      (pop-to-buffer buffer)
      (goto-char (point-min))
      (insert "  word")
      (let ((ov (make-overlay 3 7)))
        (overlay-put ov 'before-string
          #("!" 0 1 (display (left-fringe exclamation-mark error))))
        (message "Reported positions %S %S %S %S %S %S %S"
                 (posn-x-y (posn-at-point 1))
                 (posn-x-y (posn-at-point 2))
                 (posn-x-y (posn-at-point 3))
                 (posn-x-y (posn-at-point 4))
                 (posn-x-y (posn-at-point 5))
                 (posn-x-y (posn-at-point 6))
                 (posn-x-y (posn-at-point 7)))))))

bug#52097: 28.0.50; Regression - posn-at-point returns wrong result if overlay is present

[Eli Zaretskii]

> Cc: 52097@debbugs.gnu.org
> From: Daniel Mendler <mail@daniel-mendler.de>
> Date: Thu, 25 Nov 2021 12:23:02 +0100
> 
> >> 1. emacs -Q
> >> 2. Create new buffer bug.el
> >> 3. Activate flymake-mode (for the overlay)
> >> 4. Enter "  invalid-ident" (note the spaces at the beginning)
> >> 5. Wait until the flymake overlay appears
> > 
> > The overlay doesn't seem to appear for me, for some reason.
> 
> I am using emacs -Q.

So did I.

> I just recompiled the current emacs-28 branch.
> After some time flymake should underline the invalid identifier.

What can I say?  I didn't see it.

> > Could you please post a recipe that doesn't require Flymake?
> Try this command:

Thanks, this will do.

bug#52097: 28.0.50; Regression - posn-at-point returns wrong result if overlay is present

[Eli Zaretskii]

> Date: Thu, 25 Nov 2021 13:40:47 +0200
> From: Eli Zaretskii <eliz@gnu.org>
> Cc: 52097@debbugs.gnu.org
> 
> > > Could you please post a recipe that doesn't require Flymake?
> > Try this command:
> 
> Thanks, this will do.

Should be fixed now on the release branch.

bug#52097: 28.0.50; Regression - posn-at-point returns wrong result if overlay is present

[Daniel Mendler]

> Should be fixed now on the release branch.

Thank you. I confirm that the issue has been fixed.

bug#52097: 28.0.50; Regression - posn-at-point returns wrong result if overlay is present

[Eli Zaretskii]

> Cc: 52097@debbugs.gnu.org
> From: Daniel Mendler <mail@daniel-mendler.de>
> Date: Thu, 25 Nov 2021 14:52:01 +0100
> 
> > Should be fixed now on the release branch.
> 
> Thank you. I confirm that the issue has been fixed.

Thanks for testing, I'm therefore closing the bug.