lualine.nvim/lua/lualine/components/searchcount.lua

local function searchcount()
  if vim.v.hlsearch == 0 then
    return ''
  end

  local result = vim.fn.searchcount { maxcount = 999, timeout = 500 }
  local denominator = math.min(result.total, result.maxcount)
  return string.format('[%d/%d]', result.current, denominator)
end

return searchcount