nvim/lua/plugins/treesj.lua

return {
  "Wansmer/treesj",
  dependencies = { "nvim-treesitter/nvim-treesitter" },
  cmd = { "TSJToggle", "TSJJoin", "TSJSplit" },
  keys = {
    { "J", "<cmd>TSJToggle<cr>", desc = "Toggle Treesitter Join" },
    { "<space>tj", "<cmd>TSJJoin<cr>", desc = "Treesitter Join" },
    { "<space>ts", "<cmd>TSJSplit<cr>", desc = "Treesitter Split" },
  },
  config = function()
    require("treesj").setup({
      use_default_keymaps = false,
      on_error = function(err_text, level)
        if not err_text:find("splitted") then
          vim.cmd.join()
        end
      end,
    })
  end,
}