bug#56818: 28.1; c-mode font-lock issues in Emacs 28

[Bill Sacks <sacks@ucar.edu>]

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Starting with Emacs 28, I have been seeing font-lock issues when editing 
C and C++ code. The situation where I see this the most (though I'm not 
sure if it's the only situation) is when I am writing a comment and 
currently have a space at the end of the comment line: in this 
situation, the fontification of a variable name or function name on the 
next line becomes broken until I type a non-space character to end the 
current line.

The attached screen shots illustrate the problem: nospaces.png shows the 
correct fontification; space_before_var.png and 
space_before_function.png show that variable and function names lose 
their fontification when there is a space at the end of the previous 
comment line. Running M-x font-lock-fontify-buffer temporarily fixes the 
issue.

The problem occurs even when using emacs -Q. I have tried the latest 
emacs28 pretest and the latest nightly build available from 
emacsformacosx (though with my customizations – NOT with emacs -Q) and 
those also exhibit the problem. The latest emacs27 from emacsformacosx 
does NOT have this issue.

(I have also been seeing slightly similar font-lock issues when editing 
python code with Emacs 28. There, I get inconsistent fontification of 
variables: variables sometimes are not fontified with 
font-lock-variable-name-face when I initially load a file, but then if I 
edit a line – e.g., by adding a space at the end of the line – then the 
variable defined on that line will become properly fontified. I realize 
that this may be a separate issue that may warrant its own bug report, 
but I thought I'd mention it in case it's related.)

Thank you,
Bill


In GNU Emacs 28.1 (build 2, aarch64-apple-darwin21.5.0, NS 
appkit-2113.50 Version 12.4 (Build 21F79))
of 2022-07-19 built on cgdm-green
Windowing system distributor 'Apple', version 10.3.2113
System Description: macOS 12.4

Configured using:
'configure --disable-dependency-tracking --disable-silent-rules
--enable-locallisppath=/opt/homebrew/share/emacs/site-lisp
--infodir=/opt/homebrew/Cellar/emacs-plus@28/28.1/share/info/emacs
--prefix=/opt/homebrew/Cellar/emacs-plus@28/28.1 --with-xml2
--with-gnutls --with-native-compilation --without-dbus
--without-imagemagick --with-modules --with-rsvg --with-ns
--disable-ns-self-contained 'CFLAGS=-Os -w -pipe
-mmacosx-version-min=12
-isysroot/Library/Developer/CommandLineTools/SDKs/MacOSX12.sdk'
'CPPFLAGS=-I/opt/homebrew/opt/zlib/include
-I/opt/homebrew/opt/icu4c/include -I/opt/homebrew/opt/sqlite/include
-I/opt/homebrew/opt/openssl@1.1/include
-I/opt/homebrew/opt/readline/include -I/opt/homebrew/opt/libffi/include
-isystem/opt/homebrew/include -F/opt/homebrew/Frameworks
-isysroot/Library/Developer/CommandLineTools/SDKs/MacOSX12.sdk'
'LDFLAGS=-L/opt/homebrew/opt/zlib/lib -L/opt/homebrew/opt/icu4c/lib
-L/opt/homebrew/opt/sqlite/lib -L/opt/homebrew/opt/openssl@1.1/lib
-L/opt/homebrew/opt/readline/lib -L/opt/homebrew/opt/libffi/lib
-L/opt/homebrew/lib -F/opt/homebrew/Frameworks
-Wl,-headerpad_max_install_names
-isysroot/Library/Developer/CommandLineTools/SDKs/MacOSX12.sdk''

Configured features:
ACL GLIB GMP GNUTLS JPEG JSON LCMS2 LIBXML2 MODULES NATIVE_COMP NOTIFY
KQUEUE NS PDUMPER PNG RSVG THREADS TIFF TOOLKIT_SCROLL_BARS XIM ZLIB

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

Major mode: C/*l

Minor modes in effect:
tooltip-mode: t
global-eldoc-mode: t
show-paren-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
indent-tabs-mode: t
transient-mark-mode: t
abbrev-mode: t

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message rmc puny dired dired-loaddefs
rfc822 mml mml-sec epa derived epg rfc6068 epg-config gnus-util rmail
rmail-loaddefs auth-source cl-seq eieio eieio-core cl-macs
eieio-loaddefs password-cache json map text-property-search seq byte-opt
gv bytecomp byte-compile cconv mm-decode mm-bodies mm-encode mail-parse
rfc2231 mailabbrev gmm-utils mailheader sendmail rfc2047 rfc2045
ietf-drums mm-util mail-prsvr mail-utils time-date subr-x jka-compr info
vc-dispatcher vc-svn cc-mode cc-fonts cc-guess cc-menus cc-cmds
cc-styles cc-align cc-engine cc-vars cc-defs cl-loaddefs cl-lib
iso-transl tooltip eldoc paren electric uniquify ediff-hook vc-hooks
lisp-float-type elisp-mode mwheel term/ns-win ns-win ucs-normalize
mule-util term/common-win 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 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 simple abbrev obarray cl-preloaded nadvice button
loaddefs faces cus-face macroexp files window text-properties overlay
sha1 md5 base64 format env code-pages mule custom widget
hashtable-print-readable backquote threads kqueue cocoa ns lcms2
multi-tty make-network-process native-compile emacs)

Memory information:
((conses 16 107172 9071)
(symbols 48 8698 0)
(strings 32 28953 1830)
(string-bytes 1 1020321)
(vectors 16 16903)
(vector-slots 8 352351 17895)
(floats 8 29 38)
(intervals 56 546 0)
(buffers 992 13))


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