bug: Formatting with markdownlint-cli2 invalid capture index error

[nickeisenberg]

Neovim version (nvim -v)

NVIM v0.10.5

Operating system/version

Ubuntu 24.04

Read debugging tips

• [x] I have read through the debugging tips.

Add the debug logs

• [x] I have set log_level = vim.log.levels.DEBUG and pasted the log contents below.

Log file

Error executing Lua callback: ...ocal/share/nvim/lazy/conform.nvim/lua/conform/runner.lua:506: invalid capture index stack traceback: [C]: in function 'gsub' ...ocal/share/nvim/lazy/conform.nvim/lua/conform/runner.lua:506: in function 'build_context' ....local/share/nvim/lazy/conform.nvim/lua/conform/init.lua:770: in function 'get_formatter_info' ...ocal/share/nvim/lazy/conform.nvim/lua/conform/health.lua:140: in function 'append_formatters' ...ocal/share/nvim/lazy/conform.nvim/lua/conform/health.lua:159: in function 'show_window' ...s/.local/share/nvim/lazy/conform.nvim/plugin/conform.lua:2: in function <...s/.local/share/nvim/lazy/conform.nvim/plugin/conform.lua:1>

Describe the bug

I am unable to format with markdownlint-cli2.

What is the severity of this bug?

breaking (some functionality is broken)

Steps To Reproduce

1. Install using lazy

return {
  {
    "stevearc/conform.nvim",
    config = function()
      require("conform").setup({
        log_level = vim.log.levels.DEBUG,
        formatters_by_ft = {
          markdown = { "markdownlint-cli2" },
        }
      })
    end,
  },

2. Open and markdown file and run :lua require("conform").format()

3. Thats it.

Expected Behavior

I would like the current file to be formatted with markdownlint-cli2 but there is an error instead.

Minimal example file

#title

Try formatting this with conform.nvim

Minimal init.lua

-- DO NOT change the paths and don't remove the colorscheme
local root = vim.fn.fnamemodify("./.repro", ":p")

-- set stdpaths to use .repro
for _, name in ipairs({ "config", "data", "state", "cache" }) do
  vim.env[("XDG_%s_HOME"):format(name:upper())] = root .. "/" .. name
end

-- bootstrap lazy
local lazypath = root .. "/plugins/lazy.nvim"
if not vim.loop.fs_stat(lazypath) then
  vim.fn.system({
    "git",
    "clone",
    "--filter=blob:none",
    "--single-branch",
    "https://github.com/folke/lazy.nvim.git",
    lazypath,
  })
end
vim.opt.runtimepath:prepend(lazypath)

-- install plugins
local plugins = {
  "folke/tokyonight.nvim",
  {
    "stevearc/conform.nvim",
    config = function()
      require("conform").setup({
        log_level = vim.log.levels.DEBUG,
        -- add your config here
        formatters_by_ft = {
          markdown = { "markdownlint-cli2" },
        }
      })
    end,
  },
  -- add any other plugins here
}
require("lazy").setup(plugins, {
  root = root .. "/plugins",
})

vim.cmd.colorscheme("tokyonight")
-- add anything else here

Additional context

No response