Neovim crashes when editing multilevel list

[fisher-j]

Describe the bug

When editing a multilevel list, and starting a new "de-dented" list item neovim crashes without warning. Often this only happens after typing and deleting a character (with backspace) on the new item.

For instance, if I open a test.md with the following contents:

# A list

- item 1
  - sub-item
    - level three
  -

and then place my cursor on the last line, and type a space followed by some characters, and then possibly a backspace, neovim crashes.

The behavior is reproducible, but not perfectly so. To reproduce I might have to do any of the following (on the last line, after the list marker):

• type a single character
• type several characters
• type several characters followed by a backspace
• repeatedly type 1 or more chacters followed by an equal number of backspaces

I was able to reproduce this behavior when treesitter is the only plugin I load.

Once I was able to reopen the file and observe an error which I think mentioned an out of range index for extmark, but unfortunately, I have not be able to reproduce the error message.

[difeiyu]

I also encountered this problem, the same way to reproduce

## HOME
- a
    - aa
        - aaa
    - ac

vim crashes when backspace is pressed I removed all plugins except treesitter, same goes for tests

[ibash]

Maybe related: https://github.com/neovim/neovim/issues/25164

[ibash]

For posterity, you can apply the patch as per instructions here: https://github.com/neovim/neovim/issues/25164#issuecomment-1722150924

[zmre]

This bug has been killing me. Stack traces were misleading. Random quits when editing notes. Have temporarily disabled treesitter markdown but am hoping the linked PR gets accepted and a new release made. I see the workaround that uses ibash's fork, and I can make that work if necessary (though differently since I use nix), but would far rather see it fixed here. I know maintaining open source software like this can be thankless, so just want to send out a thank you to whomever (@MDeiml ?) is able to review and help get the bug fix through to a release. Thank you and thanks to @ibash for tracking it down!