Subject: bug#71819: Incorrect substitution when undo replacing regexps

From: Sab Pyrope <[email-masked]>
Date: Fri, 28 Jun 2024 08:57:03 +0800

I encountered a bug when replacing regular expressions.
If you [u]ndo a previous change during the replacement process, subsequent
changes to the \2 substitution will use the old undone result.

Text:
---
Aaaaa. Bbbb.
Ccccc. Dddd.
Eeeee. Ffff.
Ggggg. Hhhh.
---
Input regexp: \([.]\) \([A-Z]\)
Output regexp: \1  \2
Bug:
1. Copy the text above to the buffer.
2. Enter the regular expressions to the interactive regexp replacement [
C-M-%].
3. Click [y] twice until the Ffff is highlighted.
4. Cancel the previous replacement via [u].
5. Continue replacing [y] until the end.
6. Notice that all sentences except the first and second now begin with an
incorrect letter D, which is not implied by the entered regexp, it should
be F and H, as if it had been replaced, but without being undoed in the
middle of the process.
Output:
---
Aaaaa.  Bbbb.
Ccccc.  Dddd.
Eeeee.  Dfff.
Ggggg.  Dhhh.
---

In GNU Emacs 29.3 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.38,
 cairo version 1.16.0) of 2024-05-20, modified by Debian built on sbuild
Windowing system distributor 'The X.Org Foundation', version 11.0.12101007
System Description: Debian GNU/Linux 12 (bookworm)

Configured using:
 'configure --build x86_64-linux-gnu --prefix=/usr
 --sharedstatedir=/var/lib --libexecdir=/usr/libexec
 --localstatedir=/var/lib --infodir=/usr/share/info
 --mandir=/usr/share/man --with-libsystemd --with-pop=yes
 --enable-locallisppath=/etc/emacs:/usr/local/share/emacs/29.3/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/29.3/site-lisp:/usr/share/emacs/site-lisp
 --with-sound=alsa --without-gconf --with-mailutils
 --with-native-compilation --build x86_64-linux-gnu --prefix=/usr
 --sharedstatedir=/var/lib --libexecdir=/usr/libexec
 --localstatedir=/var/lib --infodir=/usr/share/info
 --mandir=/usr/share/man --with-libsystemd --with-pop=yes
 --enable-locallisppath=/etc/emacs:/usr/local/share/emacs/29.3/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/29.3/site-lisp:/usr/share/emacs/site-lisp
 --with-sound=alsa --without-gconf --with-mailutils
 --with-native-compilation --with-cairo --with-x=yes
 --with-x-toolkit=gtk3 --with-toolkit-scroll-bars 'CFLAGS=-g -O2
 -ffile-prefix-map=/build/reproducible-path/emacs-29.3+1=.
-fstack-protector-strong
 -Wformat -Werror=format-security -Wall' 'CPPFLAGS=-Wdate-time
 -D_FORTIFY_SOURCE=2' LDFLAGS=-Wl,-z,relro'

Configured features:
ACL CAIRO DBUS FREETYPE GIF GLIB GMP GNUTLS GPM GSETTINGS HARFBUZZ JPEG
JSON LCMS2 LIBOTF LIBSELINUX LIBSYSTEMD LIBXML2 M17N_FLT MODULES
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Important settings:
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  value of $LC_NUMERIC: ru_RU.UTF-8
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Major mode: Fundamental

Minor modes in effect:
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  global-tab-line-mode: t
  tab-line-mode: t
  global-display-line-numbers-mode: t
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  transient-mark-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t

Load-path shadows:
None found.

Features:
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Memory information:
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 (symbols 48 21740 133)
 (strings 32 123122 109316)
 (string-bytes 1 5309779)
 (vectors 16 36085)
 (vector-slots 8 683635 189466)
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