Break the undo sequence in normal mode

Question

Question: Is there something which is works same as i_CTRL-G_u, but for normal mode?

This would be useful in mappings (like nnoremap), because (I think, but fixme) in normal mode, if you are just typing commands (vs. a sequence mapped to a single key), then each command counts as a separate undo block.

Case in point: I'm trying to solve this exercise, from Learn Vimscript the Hard Way.

This is what I came up with, and it seems to work:

:nnoremap <leader>d ddi<C-G>u<esc>dd

While this works, it seems a bit hackish, going into insert mode just to break the undo sequence, so I was wondering if it is possible without going into insert mode.

Of course, I already tried the following variant, but all it does is deleting a single line, so it seems that the <C-G> part kind of ends the sequence:

:nnoremap <leader>d dd<C-G>udd

Answer 1

Doing :let &ul=&ul breaks the undo sequence. This is documented under :h :undojoin:

Setting the value of 'undolevels' also breaks undo. Even when the new value is equal to the old value.

Using the described method, you can do the following:

nnoremap <leader>d dd:let &ul=&ul<CR>dd

Answer 2

Most elegant in my opinion:

nnoremap <leader>dd :call feedkeys("dddd",'t')<cr>

feedkeys() function with 't' parameter pretends that the user actually typed dddd.

If you press dddd in Normal mode, you can undo first dd, and then second dd. If you create a mapping for that and use it, u undoes the whole mapped sequence at once, which is the problem introduced in the question. However, once you create a mapping using feedkeys() function with 't' parameter as in my example, you can undo each individual normal mode command from a sequence of normal mode commands given as first argument to the feedkeys() function.

Of course you cannot control the "granularity" of breaking the undo-sequence using this method. But for some uses it may be more elegant and readable.

More info: :help feedkeys().