vim/lua/custom/plugins/folding.lua

local foldIcon = ''
local hlgroup = 'NonText'
local function foldTextFormatter(virtText, lnum, endLnum, width, truncate)
  local newVirtText = {}
  local suffix = '  ' .. foldIcon .. '  ' .. tostring(endLnum - lnum)
  local sufWidth = vim.fn.strdisplaywidth(suffix)
  local targetWidth = width - sufWidth
  local curWidth = 0
  for _, chunk in ipairs(virtText) do
    local chunkText = chunk[1]
    local chunkWidth = vim.fn.strdisplaywidth(chunkText)
    if targetWidth > curWidth + chunkWidth then
      table.insert(newVirtText, chunk)
    else
      chunkText = truncate(chunkText, targetWidth - curWidth)
      local hlGroup = chunk[2]
      table.insert(newVirtText, { chunkText, hlGroup })
      chunkWidth = vim.fn.strdisplaywidth(chunkText)
      if curWidth + chunkWidth < targetWidth then
        suffix = suffix .. (' '):rep(targetWidth - curWidth - chunkWidth)
      end
      break
    end
    curWidth = curWidth + chunkWidth
  end
  table.insert(newVirtText, { suffix, hlgroup })
  return newVirtText
end

return {
  'kevinhwang91/nvim-ufo',
  dependencies = 'kevinhwang91/promise-async',
  enabled = false,
  event = 'BufReadPost',
  init = function()
    -- INFO fold commands usually change the foldlevel, which fixes folds, e.g.
    -- auto-closing them after leaving insert mode, however ufo does not seem to
    -- have equivalents for zr and zm because there is no saved fold level.
    -- Consequently, the vim-internal fold levels need to be disabled by setting
    -- them to 99
    vim.opt.foldlevel = 99
    vim.opt.foldlevelstart = 99
    vim.opt.foldcolumn = 'auto'
  end,
  opts = {
    provider_selector = function(_, ft, _)
      local lspWithOutFolding = { 'markdown', 'yaml' }
      if vim.tbl_contains(lspWithOutFolding, ft) then
        return { 'treesitter', 'indent' }
      elseif ft == 'html' then
        return { 'indent' } -- lsp & treesitter do not provide folds
      else
        return { 'lsp', 'indent' }
      end
    end,
    -- open opening the buffer, close these fold kinds
    -- use `:UfoInspect` to get available fold kinds from the LSP
    close_fold_kinds = { 'imports' },
    open_fold_hl_timeout = 500,
    fold_virt_text_handler = foldTextFormatter,
  },
}