bug#65834: 29.1; highlighting bug in CPerl mode: here-document false positive

[Vincent Lefevre]

Open a file containing the following code, in CPerl mode:

# -*- mode: cperl -*-
if ($t->[3]<<5) {
  return 0;
}
# comment

The contents are highlighted like a here-document starting at
"return 0;" probably due to the "<<" (but this is a left shift,
not a here-document declaration).

GNU Emacs 27.1, 28.2 and 29.1 are affected.

Note: I initially found when reading the "mailgraph" Perl script.


In GNU Emacs 29.1 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.38,
 cairo version 1.16.0) of 2023-08-30, modified by Debian built on
 x86-csail-01
Windowing system distributor 'The X.Org Foundation', version 11.0.12101008
System Description: Debian GNU/Linux trixie/sid

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/29.1/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/29.1/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/29.1/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/29.1/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-29.1+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
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_COLLATE: POSIX
  value of $LC_CTYPE: C.UTF-8
  value of $LC_TIME: en_DK.utf8
  value of $LANG: POSIX
  locale-coding-system: utf-8-unix

Major mode: CPerl

Minor modes in effect:
  display-time-mode: t
  tooltip-mode: t
  global-eldoc-mode: t
  show-paren-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  menu-bar-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:
/usr/share/emacs/site-lisp/llvm-10/llvm-mode hides 
/usr/share/emacs/site-lisp/llvm-11/llvm-mode
/usr/share/emacs/site-lisp/llvm-10/emacs hides 
/usr/share/emacs/site-lisp/llvm-11/emacs
/usr/share/emacs/site-lisp/llvm-10/tablegen-mode hides 
/usr/share/emacs/site-lisp/llvm-11/tablegen-mode
/usr/share/emacs/site-lisp/llvm-10/llvm-mode hides 
/usr/share/emacs/site-lisp/llvm-12/llvm-mode
/usr/share/emacs/site-lisp/llvm-10/emacs hides 
/usr/share/emacs/site-lisp/llvm-12/emacs
/usr/share/emacs/site-lisp/llvm-10/tablegen-mode hides 
/usr/share/emacs/site-lisp/llvm-12/tablegen-mode
/usr/share/emacs/site-lisp/llvm-10/llvm-mode hides 
/usr/share/emacs/site-lisp/llvm-13/llvm-mode
/usr/share/emacs/site-lisp/llvm-10/emacs hides 
/usr/share/emacs/site-lisp/llvm-13/emacs
/usr/share/emacs/site-lisp/llvm-10/tablegen-mode hides 
/usr/share/emacs/site-lisp/llvm-13/tablegen-mode
/usr/share/emacs/site-lisp/llvm-10/llvm-mode hides 
/usr/share/emacs/site-lisp/llvm-14/llvm-mode
/usr/share/emacs/site-lisp/llvm-10/emacs hides 
/usr/share/emacs/site-lisp/llvm-14/emacs
/usr/share/emacs/site-lisp/llvm-10/tablegen-mode hides 
/usr/share/emacs/site-lisp/llvm-14/tablegen-mode
/usr/share/emacs/site-lisp/llvm-10/llvm-mode hides 
/usr/share/emacs/site-lisp/llvm-15/llvm-mode
/usr/share/emacs/site-lisp/llvm-10/emacs hides 
/usr/share/emacs/site-lisp/llvm-15/emacs
/usr/share/emacs/site-lisp/llvm-10/tablegen-mode hides 
/usr/share/emacs/site-lisp/llvm-15/tablegen-mode
/usr/share/emacs/site-lisp/llvm-10/llvm-mode hides 
/usr/share/emacs/site-lisp/llvm-16/llvm-mode
/usr/share/emacs/site-lisp/llvm-10/emacs hides 
/usr/share/emacs/site-lisp/llvm-16/emacs
/usr/share/emacs/site-lisp/llvm-10/tablegen-mode hides 
/usr/share/emacs/site-lisp/llvm-16/tablegen-mode
/usr/share/emacs/site-lisp/llvm-10/llvm-mode hides 
/usr/share/emacs/site-lisp/llvm-3.5/llvm-mode
/usr/share/emacs/site-lisp/llvm-10/emacs hides 
/usr/share/emacs/site-lisp/llvm-3.5/emacs
/usr/share/emacs/site-lisp/llvm-10/tablegen-mode hides 
/usr/share/emacs/site-lisp/llvm-3.5/tablegen-mode
/usr/share/emacs/site-lisp/llvm-10/llvm-mode hides 
/usr/share/emacs/site-lisp/llvm-3.6/llvm-mode
/usr/share/emacs/site-lisp/llvm-10/emacs hides 
/usr/share/emacs/site-lisp/llvm-3.6/emacs
/usr/share/emacs/site-lisp/llvm-10/tablegen-mode hides 
/usr/share/emacs/site-lisp/llvm-3.6/tablegen-mode
/usr/share/emacs/site-lisp/llvm-10/llvm-mode hides 
/usr/share/emacs/site-lisp/llvm-3.7/llvm-mode
/usr/share/emacs/site-lisp/llvm-10/emacs hides 
/usr/share/emacs/site-lisp/llvm-3.7/emacs
/usr/share/emacs/site-lisp/llvm-10/tablegen-mode hides 
/usr/share/emacs/site-lisp/llvm-3.7/tablegen-mode
/usr/share/emacs/site-lisp/llvm-10/llvm-mode hides 
/usr/share/emacs/site-lisp/llvm-7/llvm-mode
/usr/share/emacs/site-lisp/llvm-10/emacs hides 
/usr/share/emacs/site-lisp/llvm-7/emacs
/usr/share/emacs/site-lisp/llvm-10/tablegen-mode hides 
/usr/share/emacs/site-lisp/llvm-7/tablegen-mode
/usr/share/emacs/site-lisp/llvm-10/llvm-mode hides 
/usr/share/emacs/site-lisp/llvm-8/llvm-mode
/usr/share/emacs/site-lisp/llvm-10/emacs hides 
/usr/share/emacs/site-lisp/llvm-8/emacs
/usr/share/emacs/site-lisp/llvm-10/tablegen-mode hides 
/usr/share/emacs/site-lisp/llvm-8/tablegen-mode
/usr/share/emacs/site-lisp/llvm-10/llvm-mode hides 
/usr/share/emacs/site-lisp/llvm-9/llvm-mode
/usr/share/emacs/site-lisp/llvm-10/emacs hides 
/usr/share/emacs/site-lisp/llvm-9/emacs
/usr/share/emacs/site-lisp/llvm-10/tablegen-mode hides 
/usr/share/emacs/site-lisp/llvm-9/tablegen-mode
/usr/share/emacs/site-lisp/elpa/po-mode-0.21/po-mode hides 
/usr/share/emacs/site-lisp/elpa-src/po-mode-0.21/po-mode
/usr/share/emacs/site-lisp/elpa/po-mode-0.21/po-mode-pkg hides 
/usr/share/emacs/site-lisp/elpa-src/po-mode-0.21/po-mode-pkg
/usr/share/emacs/site-lisp/elpa/po-mode-0.21/po-mode-autoloads hides 
/usr/share/emacs/site-lisp/elpa-src/po-mode-0.21/po-mode-autoloads
/usr/share/emacs/site-lisp/latex-cjk-thai/thai-word hides 
/usr/share/emacs/29.1/lisp/language/thai-word

Features:
(shadow sort mail-extr emacsbug message yank-media puny dired
dired-loaddefs rfc822 mml mml-sec epa derived epg rfc6068 epg-config
gnus-util text-property-search time-date mm-decode mm-bodies mm-encode
mail-parse rfc2231 mailabbrev gmm-utils mailheader sendmail rfc2047
rfc2045 ietf-drums mm-util mail-prsvr mail-utils comp comp-cstr warnings
cl-extra help-mode cperl-mode rx facemenu cus-edit pp cus-start icons
wid-edit time cus-load cc-styles cc-align cc-engine cc-vars cc-defs
mmm-auto mmm-vars mmm-utils mmm-compat package browse-url url url-proxy
url-privacy url-expand url-methods url-history url-cookie
generate-lisp-file url-domsuf url-util mailcap url-handlers url-parse
auth-source cl-seq eieio eieio-core cl-macs password-cache json subr-x
map byte-opt gv bytecomp byte-compile url-vars cl-loaddefs cl-lib 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 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 move-toolbar gtk x-toolkit xinput2 x multi-tty
make-network-process native-compile emacs)

Memory information:
((conses 16 153873 9302)
 (symbols 48 12400 1)
 (strings 32 36098 2125)
 (string-bytes 1 1153829)
 (vectors 16 22304)
 (vector-slots 8 679647 81235)
 (floats 8 50 40)
 (intervals 56 318 0)
 (buffers 984 13))