bug#70367: 30.0.50; Inconsistent Syntax Highlighting

[Stephen Berman via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>]

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.

Steve Berman