GNU bug report logs - #64063
smerge-mode highlight gets stuck if buffer autoreverted "delicately"

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Konstantin Kharlamov <hi-angel <at> yandex.ru>
To: bug-gnu-emacs <at> gnu.org
Subject: smerge-mode highlight gets stuck if buffer autoreverted "delicately"
Date: Wed, 14 Jun 2023 14:16:47 +0300

Basically, when autorevert is on and the file reverted contains a conflict, the
conflict is highlighted. Then if you remove the conflict by external means, and
Emacs autoreverts the buffer again, the conflict highlight usually gets removed.
However, if autorevert is using `revert-buffer-insert-file-contents-delicately`,
the highlight gets stuck.


# Steps to reproduce

1. Create `/tmp/.emacs` with the following content:

    (require 'autorevert)
    ;; Do not break markers in a buffer upon reverting a buffer. Details:
    ;; https://github.com/magit/magit/issues/4442
    (setq revert-buffer-insert-file-contents-function 'revert-buffer-insert-
file-contents-delicately)
    (global-auto-revert-mode 1)

2. In a terminal, enter Emacs source-code repository, and create a conflict by
executing:

    git checkout 5cace109d2 && git cherry-pick f24ea84f430

3. Open Emacs as `HOME=/tmp emacs etc/NEWS`. Note a conflict line that Emacs
automatically jumped to.
4. In a terminal, execute `git cherry-pick --abort` and wait for Emacs to revert
the buffer. Note that buffer no longer has conflict.

## Expected

The reverted buffer does not have word "user option" highlighted

## Actual

The reverted buffer has word "user option" highlighted in red.

------------------

In GNU Emacs 30.0.50 (build 1, x86_64-pc-linux-gnu, GTK+ Version
 3.24.38, cairo version 1.17.8) of 2023-05-31 built on constantine-N61Ja
Repository revision: 5cace109d2bce98a7d486e44378286031465f40f
Repository branch: fix-smerge-highlight
Windowing system distributor 'The X.Org Foundation', version 11.0.12101008
System Description: Arch Linux

Configured using:
 'configure --prefix=/usr --sysconfdir=/etc --libexecdir=/usr/lib
 --localstatedir=/var --mandir=/usr/share/man --with-gameuser=:games
 --with-modules --without-libotf --without-m17n-flt --without-gconf
 --enable-link-time-optimization --with-native-compilation=yes
 --with-xinput2 --with-x-toolkit=gtk3 --without-xaw3d --with-sound=no
 --with-tree-sitter --without-gpm --without-compress-install
 '--program-transform-name=s/\([ec]tags\)/\1.emacs/' 'CFLAGS=-Wno-error
 -flto=2 -march=native -O3 -pipe -fno-stack-protector -fweb
 -fmerge-all-constants -fno-plt -fcommon' 'LDFLAGS=-flto=2 -O3
 -march=native -fweb -fmerge-all-constants -floop-nest-optimize
 -Wl,--sort-common,-z,relro -fno-plt -fcommon''

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

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

Major mode: Shell-script

Minor modes in effect:
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  yas-global-mode: t
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  highlight-parentheses-mode: t
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  global-auto-revert-mode: t
  auto-revert-mode: t
  company-flx-mode: t
  global-company-mode: t
  company-mode: t
  override-global-mode: t
  tooltip-mode: t
  global-eldoc-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  column-number-mode: t
  line-number-mode: t
  transient-mark-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t

Load-path shadows:
~/.emacs.d/lisp/popup hides /home/constantine/.emacs.d/elpa/popup-
20211231.1823/popup
~/.emacs.d/lisp/idomenu hides /home/constantine/.emacs.d/elpa/idomenu-
20141123.2120/idomenu
/home/constantine/.emacs.d/elpa/cmake-mode-20220322.1258/cmake-mode hides
/usr/share/emacs/site-lisp/cmake-mode
/home/constantine/.emacs.d/elpa/ninja-mode-20181024.1439/ninja-mode hides
/usr/share/emacs/site-lisp/ninja-mode
/home/constantine/.emacs.d/elpa/transient-20220406.1156/transient hides
/usr/share/emacs/30.0.50/lisp/transient
/home/constantine/.emacs.d/elpa/use-package-20210207.1926/use-package hides
/usr/share/emacs/30.0.50/lisp/use-package/use-package
/home/constantine/.emacs.d/elpa/use-package-20210207.1926/use-package-lint hides
/usr/share/emacs/30.0.50/lisp/use-package/use-package-lint
/home/constantine/.emacs.d/elpa/use-package-20210207.1926/use-package-jump hides
/usr/share/emacs/30.0.50/lisp/use-package/use-package-jump
/home/constantine/.emacs.d/elpa/use-package-20210207.1926/use-package-ensure
hides /usr/share/emacs/30.0.50/lisp/use-package/use-package-ensure
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hides /usr/share/emacs/30.0.50/lisp/use-package/use-package-diminish
/home/constantine/.emacs.d/elpa/use-package-20210207.1926/use-package-delight
hides /usr/share/emacs/30.0.50/lisp/use-package/use-package-delight
/home/constantine/.emacs.d/elpa/use-package-20210207.1926/use-package-core hides
/usr/share/emacs/30.0.50/lisp/use-package/use-package-core
/home/constantine/.emacs.d/elpa/use-package-20210207.1926/use-package-bind-key
hides /usr/share/emacs/30.0.50/lisp/use-package/use-package-bind-key
/home/constantine/.emacs.d/elpa/bind-key-20210210.1609/bind-key hides
/usr/share/emacs/30.0.50/lisp/use-package/bind-key
/home/constantine/.emacs.d/elpa/let-alist-1.0.6/let-alist hides
/usr/share/emacs/30.0.50/lisp/emacs-lisp/let-alist

Features:
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sh-script treesit executable smartparens-markdown markdown-mode noutline
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Memory information:
((conses 16 830707 760363)
 (symbols 48 33187 0)
 (strings 32 209268 43537)
 (string-bytes 1 6269384)
 (vectors 16 101229)
 (vector-slots 8 3036394 730693)
 (floats 8 456 39245)
 (intervals 56 35797 24006)
 (buffers 984 61))

Message #8 received at 64063 <at> debbugs.gnu.org (full text, mbox):

From: Konstantin Kharlamov <hi-angel <at> yandex.ru>
To: 64063 <at> debbugs.gnu.org
Cc: mardani29 <at> yahoo.es, emacs-devel <at> gnu.org
Subject: smerge-mode highlight gets stuck if buffer autoreverted "delicately"
Date: Sat, 17 Jun 2023 03:16:32 +0300

On Thu, 2023-06-01 at 13:35 +0200, Daniel Martín wrote:
> > So, my question is, what "on change" hooks smerge-mode uses to detect that a
> > change to the buffer has been made to check whether conflict markers are still
> > in place? I tried searching for the word "hook" over the smerge-mode.el but
> > didn't find anything relevant.
>
> If font-lock is enabled, smerge-mode uses it to fontify the conflicting
> regions.  See smerge-font-lock-keywords.  So perhaps the regular
> font-lock debugging techniques might help you investigate this issue in
> more detail.

So, I think the problem is that the highlight that gets stuck does not use font-lock,
or at least not through means of `smerge-font-lock-keywords`. Whatever is defined in
`smerge-font-lock-keywords` gets unhighlighted correctly. But the part that gets
stuck instead is an overlay.

So I presume besides font-lock-mode there's some other highlight management ongoing,
the one that decides whether to put/remove overlays over some text.

Message #11 received at 64063 <at> debbugs.gnu.org (full text, mbox):

From: Konstantin Kharlamov <hi-angel <at> yandex.ru>
To: 64063 <at> debbugs.gnu.org
Cc: mardani29 <at> yahoo.es, emacs-devel <at> gnu.org
Subject: Re: smerge-mode highlight gets stuck if buffer autoreverted
 "delicately"
Date: Sat, 17 Jun 2023 03:39:20 +0300

On Sat, 2023-06-17 at 03:16 +0300, Konstantin Kharlamov wrote:
> On Thu, 2023-06-01 at 13:35 +0200, Daniel Martín wrote:
> > > So, my question is, what "on change" hooks smerge-mode uses to detect that
> > > a
> > > change to the buffer has been made to check whether conflict markers are
> > > still
> > > in place? I tried searching for the word "hook" over the smerge-mode.el
> > > but
> > > didn't find anything relevant.
> > 
> > If font-lock is enabled, smerge-mode uses it to fontify the conflicting
> > regions.  See smerge-font-lock-keywords.  So perhaps the regular
> > font-lock debugging techniques might help you investigate this issue in
> > more detail.
> 
> So, I think the problem is that the highlight that gets stuck does not use
> font-lock,
> or at least not through means of `smerge-font-lock-keywords`. Whatever is
> defined in
> `smerge-font-lock-keywords` gets unhighlighted correctly. But the part that
> gets
> stuck instead is an overlay.
> 
> So I presume besides font-lock-mode there's some other highlight management
> ongoing,
> the one that decides whether to put/remove overlays over some text.

Okay, I think I figured it out. The hook upon which stuff gets highlighted is
`find-file-hook`. It calls vc, vc calls smerge, which checks if there's any
conflict markers; then finally `(smerge-refine)` gets called which adds the
problematic overlay.

I'm not quite sure though what is the correct fix in this case. The problem
appears when autorevert-mode is enabled, so one way may be always adding a hook
to `after-revert-hook` that clears up the overlays.

But there *may* be some other way. I notice that if I remove a conflict marker
manually, this makes the overlay disappear. I don't know what exactly causes
that to happen, but the answer to this may hide another possibility to fix the
bug. If anybody has the knowledge I will be glad to hear C:

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