Extmarks not updated correctly in nvim_buf_attach on_lines event when using :m

[TheBlob42]

Problem

Setting extmarks in the on_lines event of nvim_buf_attach for the updated lines results in wrong results when lines are moved via the :m command (e.g. :m .+2). When "moving" the line by cutting and pasting these problems do not occur, so it seems like specifically related to the :m command.

Wrapping the code for clearing the namespace and setting the extmarks into vim.schedule(...) makes it work.

Maybe this is related to #28107

Steps to reproduce

Use the following minimal.lua file:

local ns = vim.api.nvim_create_namespace('test')
vim.api.nvim_buf_attach(0, false, {
        on_lines = function(_,_,_,fl,_,llu)
            vim.print(fl .. ':' .. llu)

            vim.api.nvim_buf_clear_namespace(0, ns, fl, llu)

            for i = fl, llu - 1 do
                local first_char = vim.api.nvim_buf_get_lines(0, i, i + 1, false)[1]:sub(1, 1)
                vim.api.nvim_buf_set_extmark(0, ns, i, 0, {
                    virt_text = {{ first_char, 'WarningMsg' }},
                })
            end
        end
    }
)

• start neovim using nvim -u NONE minimal.lua
• source the minimal.lua file using source %
• add a few new rows
  • every new row contains an extmark displaying first char of the line (only for demonstration purposes)
• move one of the new lines up or down using the :m command (e.g. :m .+3)
  • the adjacent line to the moved line has the same (incorrect) extmark
  • the others have been updated accordingly

Expected behavior

The extmarks are all updated correctly even when using the :m command

Neovim version (nvim -v)

0.10.0

Vim (not Nvim) behaves the same?

not applicable

Operating system/version

Ubuntu 20.04.6 LTS

Terminal name/version

GNOME Terminal 3.36.2

$TERM environment variable

xterm-256color

Installation

appimage