nvim/lua/config/barbar.lua

require("bufferline").setup({
    options = {
        diagnostics = "coc",
        diagnostics_indicator = function(count, level, diagnostics_dict, context)
            local s = " "
            for e, n in pairs(diagnostics_dict) do
                local sym = e == "error" and " " or
                                (e == "warning" and " " or " ")
                s = s .. n .. sym
            end
            return s
        end,
        always_show_bufferline = true,
        offsets = {
            {filetype = "NvimTree", text = "Explorer", text_align = "center"},
            {filetype = "snacks_layout_box"}
        },
        vim.api.nvim_create_autocmd({"BufAdd", "BufDelete"},
                                    {
            callback = function()
                vim.schedule(function() pcall(nvim_bufferline) end)
            end
        })
    }
})