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,
        }),
    },
}