How to remove Neovim trailing white space?

Question

In Vim I used autocmd BufWritePre * :%s/\s\+$//e to delete trailing white space on save. Now, Neovim 0.7 has the new vim.api.nvim_create_autocmd.

What is the correct syntax to adapt this autocmd in Lua?

vim.api.nvim_create_autocmd("BufWritePre", {
  group = "Format",
  buffer = bufnr,
  ...
})

Answer 1

This should do the trick:

vim.api.nvim_create_autocmd({ "BufWritePre" }, {
  pattern = { "*" },
  command = [[%s/\s\+$//e]],
})

Be sure to read the h:nvim_create_autocmd() for more info!

Answer 2

I agree with the accepted answer.
Something that begins to annoy quickly is that the cursor position is reset to the beginning of the line.
To keep it, one can use getpos/setpos like this:

vim.api.nvim_create_autocmd({ "BufWritePre" }, {
    pattern = {"*"},
    callback = function(ev)
        save_cursor = vim.fn.getpos(".")
        vim.cmd([[%s/\s\+$//e]])
        vim.fn.setpos(".", save_cursor)
    end,
})

To catch errors use pcall()

vim.api.nvim_create_autocmd({ "BufWritePre" }, {
    pattern = {"*"},
    callback = function()
      local save_cursor = vim.fn.getpos(".")
      pcall(function() vim.cmd [[%s/\s\+$//e]] end)
      vim.fn.setpos(".", save_cursor)
    end,
})

Answer 3

This could also be setup to only run on a keyboard shortcut.

The following command when executed in n - Normal Mode followed by the Leader key \ + wt.

vim.keymap.set('n', '<Leader>wt', [[:%s/\s\+$//e<cr>]])
-- mode     ----^
-- shortcut ---------^
-- command  ----------------------^

I like to go one step further and wire up the lsp format command like the following example, notice the <bar> symbol allows for multiple commands:

vim.keymap.set('n', '<Leader>wt', [[:lua vim.lsp.buf.format()<cr> <bar> :%s/\s\+$//e<cr>]])
-- mode     ----^
-- shortcut ---------^
-- command1  -----------------------^
-- bar      ------------------------------------------------------^
-- command2  -----------------------------------------------------------^