bug#70367: 30.0.50; Inconsistent Syntax Highlighting

[Amol Surati]

On Sun, 14 Apr 2024 at 00:35, Eli Zaretskii <eliz@gnu.org> wrote:
>
> > From: Stephen Berman <stephen.berman@gmx.net>
> > Cc: suratiamol@gmail.com,  70367@debbugs.gnu.org
> > Date: Sat, 13 Apr 2024 21:00:16 +0200
> >
> > On Sat, 13 Apr 2024 20:48:28 +0300 Eli Zaretskii <eliz@gnu.org> wrote:
> >
> > >> Cc: 70367@debbugs.gnu.org
> > >> Date: Sat, 13 Apr 2024 20:44:37 +0300
> > >> From: Eli Zaretskii <eliz@gnu.org>
> > >>
> > >> > From: Amol Surati <suratiamol@gmail.com>
> > >> > Date: Sat, 13 Apr 2024 18:12:54 +0530
> > >> >
> > >> > The problem is not found in terminal emacs built from the released 
> > >> > 29.3.tar.gz,
> > >> > or with emacs running under GUI (i.e. under PGTK).
> > >> >
> > >> > The problem is seen with terminal emacs built from the master branch, 
> > >> > at various
> > >> > commit levels.
> > >> >
> > >> > Problem: When a large file (for e.g. vulkan_core.h) is opened, certain
> > >> > constructs have their syntax highlighting broken. The video found at 
> > >> > [1] shows
> > >> > the behaviour. At the end of the video, one can see one instance of 
> > >> > the problem;
> > >> > the syntax highlighting for the enum constant
> > >> > 'VK_STRUCTURE_TYPE_EVENT_CREATE_INFO = 10,' abruptly breaks. The entire
> > >> > identifier VK_STRUCTURE_TYPE_EVENT_CREATE_INFO must be one colour. 
> > >> > Instead,
> > >> > 'VK_STRUCTURE_TYPE_EVENT_CREA' is of the expected colour, while
> > >> > 'TE_INFO' is of the colour that is expected with '= 10,'. You may want 
> > >> > to
> > >> > download the video and then play it, if Google Drive plays it at a 
> > >> > resolution
> > >> > that is lower than the video's native resolution.
> > >> >
> > >> > Within this same session, there were other such enum constants with 
> > >> > broken
> > >> > highlighting, though they have not been captured in the video.
> > >> > The termscript is attached at [2].
> > >> >
> > >> > The graphics session is Wayland with swaywm as its compositor; 
> > >> > XWayland is
> > >> > not enabled. The terminal emulator is 'foot'. Another terminal 
> > >> > emulator,
> > >> > 'alacritty' was also tested; the problem occurred there too.
> > >> >
> > >> > The problem doesn't seem to occur with small-sized files; After 
> > >> > reducing the
> > >> > vulkan_core.h to contain only around 235 lines, emacs was able to show 
> > >> > the
> > >> > (reduced) file with consistent highlighting.
> > >>
> > >> FWIW, I cannot reproduce this with stock Emacs 29.3 and vulkan_core.h
> > >> file that I downloaded from this site:
> > >>
> > >>   https://github.com/KhronosGroup/dfdutils/blob/main/vulkan/vulkan_core.h
> > >
> > > I see now that you say you see this with the master branch, so I
> > > tested that version as well, and I still don't see the problem.
> >
> > I see exactly the same misfontification as the OP in the same file
> > (which I happen to have on my system), as well as several more similar
> > misfontifications further down in that file -- but only with c-mode from
> > cc-mode.el.  With c-ts-mode I see no misfontifications in that file.
> > This is with GNU Emacs 30.0.50 (build 1, x86_64-pc-linux-gnu, GTK+
> > Version 3.24.41, cairo version 1.18.0) of 2024-04-11.
>
> Strange.  I see no misfontifications with either mode.

Apologies. I missed Eli's email about the C modes.

My emacs build is devoid of most of the settings and
features, including GUI and tree-sitter (the config command is in
the original report). So it is likely that only cc-mode is affected,
and not c-ts-mode.

Note also that vulkan_core.h isn't special. A C source/header file
with a long enough enum definition also works. Attached is a C
program that generates to stdout the contents of such a header
file. Opening the contents (after they are saved to a file by stdout
redirection, etc.) in emacs demonstrates the problem.

-Amol

>
> Alan, would you please have a look?

repro.c
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