Neovim becomes very slow when opening an ass file

[benqhdri]

Problem

When I set syntax on, even if I opened nvim with nvim --clean, editting an ass file would be very slow.

neovim version:

NVIM v0.9.4
Build type: Release
LuaJIT 2.1.1692716794

   system vimrc file: "$VIM/sysinit.vim"
  fall-back for $VIM: "/__w/neovim/neovim/build/nvim.AppDir/usr/share/nvim"

Run :checkhealth for more info

example ass file I used to test:
https://github.com/EugeneLiu/translationCSAPP/blob/master/subtitle/translation/Lecture%2001%20%20course_overview.ass

Steps to reproduce

*copy the ass file from https://github.com/EugeneLiu/translationCSAPP/blob/master/subtitle/translation/Lecture%2001%20%20course_overview.ass
*
nvim --clean Lecture\ 01\ \ course_overview.ass

Expected behavior

Expect neovim not be that slow :)

Neovim version (nvim -v)

NVIM v0.9.4

Vim (not Nvim) behaves the same?

No(vim would not highlight ass file after syntax on). Vim version: 8.2

Operating system/version

ubuntu 22(wsl)

Terminal name/version

windows terminal 1.18.230526002-preview

$TERM environment variable

screen-256color

Installation

download the release version

[duarm]

Can't reproduce with nvim -u NONE, can reproduce with nvim --clean, running syntax off fixes the problem.

[clason]

You should never use syntax on in Neovim.

[duarm]

with nvim --noplugin -u NORC , syntax is set to ssa(same as ass), shouldn't syntax off be the default in neovim? Added

vim.cmd [[ syntax off ]]

as a workaround, pretty sure I had this, but removed it since it became the default

:verbose set syntax
  syntax=ssa
        Last set from /usr/share/nvim/runtime/syntax/syntax.vim line 35

[clason]

@zeertzjq feel free to enlighten us.

[duarm]

since the ass format is almost an .ini, I made a quick tree-sitter parser for it using the .ini as a base, since I needed it too. It runs much better https://gitlab.com/duarm1/tree-sitter-ass