bug#54992: 29.0.50; python.el: custom type hint in assignment statements is font-locked as a variable

[kobarity]

X-Debbugs-CC: Dario Gjorgjevski <dario.gjorgjevski@gmail.com>

Hi,

This is a separation of bugs mentioned in #51362 Message #24.

When the following file is loaded using emacs -Q and M-x find-file,
CustomInt in the last line is font-locked as a variable name.

#+begin_src python
from typing import List
CustomInt = int
YS: List[CustomInt] = []
#+end_src

Type hints should not be highlighted as variable names.

This is caused by the font-lock rule for special cases of assignment
statements such as '[a] = 5,'. I suggest applying the following patch
to restrict the rule not to match type hints.

diff --git a/lisp/progmodes/python.el b/lisp/progmodes/python.el
index c4d8b123a8..f355055806 100644
--- a/lisp/progmodes/python.el
+++ b/lisp/progmodes/python.el
@@ -706,7 +706,8 @@ python-font-lock-keywords-maximum-decoration
     ;;   [a] = 5
     ;;   [*a] = 5, 6
     (,(python-font-lock-assignment-matcher
-       (python-rx (or "[" "(") (* space)
+       (python-rx (or line-start ?\;) (* space)
+                  (or "[" "(") (* space)
                   grouped-assignment-target (* space)
                   (or ")" "]") (* space)
                   assignment-operator))

In GNU Emacs 29.0.50 (build 3, x86_64-pc-linux-gnu)
 of 2022-04-16 built on ubuntu
Repository revision: db416ae04982d7cf5c6af463d0c47c902f8d9119
Repository branch: master
System Description: Ubuntu 21.10

Configured using:
 'configure --without-x --with-gnutls=ifavailable'

Configured features:
ACL LIBXML2 MODULES NOTIFY INOTIFY PDUMPER SECCOMP SOUND SQLITE3 THREADS
XIM ZLIB

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
  show-paren-mode: t
  electric-indent-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  line-number-mode: t
  indent-tabs-mode: t
  transient-mark-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t

Load-path shadows:
None found.

Features:
(shadow regexp-opt sort mail-extr emacsbug message mailcap yank-media
rmc puny dired dired-loaddefs rfc822 mml mml-sec password-cache 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 cl-loaddefs cl-lib sendmail rfc2047 rfc2045 ietf-drums
mm-util mail-prsvr mail-utils term/screen term/xterm xterm seq gv subr-x
byte-opt bytecomp byte-compile cconv iso-transl tooltip eldoc paren
electric uniquify ediff-hook vc-hooks lisp-float-type elisp-mode
tabulated-list replace newcomment text-mode lisp-mode prog-mode register
page tab-bar menu-bar rfn-eshadow isearch easymenu timer select mouse
jit-lock font-lock syntax font-core term/tty-colors frame minibuffer
nadvice simple 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 emoji-zwj charscript charprop case-table epa-hook
jka-cmpr-hook help abbrev obarray oclosure cl-preloaded button 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 inotify multi-tty
make-network-process emacs)

Memory information:
((conses 16 45429 6400)
 (symbols 48 5661 1)
 (strings 32 15693 1667)
 (string-bytes 1 499770)
 (vectors 16 8641)
 (vector-slots 8 104321 5828)
 (floats 8 23 236)
 (intervals 56 202 0)
 (buffers 992 11))