GNU bug report logs - #59816
29.0.60; c++-ts-mode handles one-line comments badly

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From: Herman, Géza <geza.herman <at> gmail.com>
To: 59816 <at> debbugs.gnu.org
Subject: bug#59816: 29.0.60; c++-ts-mode handles one-line comments badly
Date: Sun, 4 Dec 2022 13:58:52 +0100

With the following simple program, emacs reports that "int a;" is in a 
comment:

---------------------
void foo() {
   // c
   int a;
}
---------------------

Repro steps:
- install tree-sitter-cpp available at 
https://github.com/tree-sitter/tree-sitter-cpp
- copy the program above into a buffer
- switch to c++-ts-mode
- at the line "int a;", put the cursor at the 'i' (or anywhere in the 
line, exact position doesn't seem to matter)
- M-: (nth 4 (syntax-ppss (point)))

For me, this incorrectly returns "t". In c++-mode (without tree sitter), 
this correctly returns "nil".

If I replace "// c" with "/* c */", the bug doesn't happen. It seems 
that one line comments don't end at the end of the line but last until 
the end of the buffer.

The AST looks like this (with both comment styles there are the same) 
using treesit-explore-mode:

(function_definition type: (primitive_type)
 declarator:
  (function_declarator declarator: (identifier)
   parameters: (parameter_list ( )))
 body:
  (compound_statement { (comment)
   (declaration type: (primitive_type) declarator: (identifier) ;)
   }))

Note I'm not sure whether this is an emacs, tree-sitter or 
tree-sitter-cpp bug. But because the AST is the same for /* */ kind of 
comment, and also if press RET on "(comment)" then only the "// c" 
comment is highlighted (so tree-sitter reports the correct area for the 
comment), I suppose that this is an emacs-related problem.


In GNU Emacs 29.0.60 (build 1, x86_64-pc-linux-gnu, GTK+ Version
 3.24.20, cairo version 1.16.0) of 2022-12-04 built on zetor
Repository revision: 84214578f5a2ff0d45312d9385442583f6877fb5
Repository branch: HEAD
Windowing system distributor 'The X.Org Foundation', version 11.0.12008000
System Description: Debian GNU/Linux bullseye/sid

Configured using:
 'configure --with-native-compilation --without-compress-install
 --with-xinput2 --with-xwidgets --with-tree-sitter
 'CFLAGS=-fno-omit-frame-pointer -g3 -O2''

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 X11 XDBE XIM XINPUT2 XPM
XWIDGETS GTK3 ZLIB

Important settings:
  value of $LC_ALL: C.UTF-8
  value of $LANG: en_US.UTF-8
  value of $XMODIFIERS: @im=none
  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
  line-number-mode: t
  indent-tabs-mode: t
  transient-mark-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  abbrev-mode: t

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message mailcap yank-media 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 sendmail
rfc2047 rfc2045 ietf-drums mm-util mail-prsvr mail-utils cc-mode
cc-fonts cc-guess cc-menus cc-cmds cc-styles cc-align cc-engine cc-vars
cc-defs c-ts-mode treesit cl-loaddefs comp comp-cstr warnings icons
subr-x rx cl-seq cl-macs gv cl-extra help-mode bytecomp byte-compile
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 xwidget-internal 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 108555 6531)
 (symbols 48 9153 0)
 (strings 32 26241 1411)
 (string-bytes 1 905477)
 (vectors 16 18498)
 (vector-slots 8 368704 14814)
 (floats 8 42 316)
 (intervals 56 400 0)
 (buffers 992 11))

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