In the master branch, insert the following code into a buffer and
activate cperl-mode:

# ---
sub just_for_indenting {
    my $here = <<HERE;
    test for a not indented here-doc containing
    HERE
    which should not terminate the here-doc
HERE
    return;
}
# ---

This is an old-style HERE-document which is terminated by the string
"HERE" which starts in the leftmost column.  cperl-mode in the master
branch wrongly uses the first occurrence of "HERE" to terminate the
string, resulting in badly fontified / indented code which follows.

The bug was introduced by an incomplete fix for (Bug:#27254) to support
indented HERE-documents in the commit
2017-07-12T15:07:55Z!vividsnow@gmail.com.

A patch to cover this edge case is attached.


In GNU Emacs 28.0.50 (build 1, x86_64-pc-linux-gnu, X toolkit, Xaw
scroll bars)
 of 2020-07-07 built on hajtower
Repository revision: 6b80ff3c465f87a31ccaaf41b2b521075f43632d
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 11.0.12004000
System Description: Debian GNU/Linux 10 (buster)

Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.

Configured features:
XPM JPEG TIFF GIF PNG SOUND NOTIFY INOTIFY GNUTLS LIBXML2 ZLIB
TOOLKIT_SCROLL_BARS LUCID X11 XDBE XIM MODULES THREADS PDUMPER GMP

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

Major mode: Lisp Interaction

Minor modes in effect:
  tooltip-mode: t
  global-eldoc-mode: t
  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
  transient-mark-mode: t

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message rmc puny dired dired-loaddefs
rfc822 mml easymenu mml-sec password-cache epa derived epg epg-config
gnus-util rmail rmail-loaddefs text-property-search time-date subr-x seq
byte-opt gv bytecomp byte-compile cconv 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
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
timer select scroll-bar mouse jit-lock font-lock syntax facemenu
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 loaddefs button faces cus-face macroexp files
text-properties overlay sha1 md5 base64 format env code-pages mule
custom widget hashtable-print-readable backquote threads inotify
dynamic-setting x-toolkit x multi-tty make-network-process emacs)

Memory information:
((conses 16 45105 8978)
 (symbols 48 6124 1)
 (strings 32 16147 1957)
 (string-bytes 1 511756)
 (vectors 16 9750)
 (vector-slots 8 164900 10931)
 (floats 8 21 43)
 (intervals 56 200 0)
 (buffers 992 10))