Undo calls changed_lines before on_bytes

[tomtomjhj]

Problem

Undo (u) calls changed_lines() before adjusting extmarks (which triggers on_bytes):

neovim/src/nvim/undo.c

Lines 2378 to 2430 in 096211a

	changed_lines(curbuf, top + 1, 0, bot, newsize - oldsize, do_buf_event);
	// When text has been changed, possibly the start of the next line
	// may have SpellCap that should be removed or it needs to be
	// displayed. Schedule the next line for redrawing just in case.
	if (spell_check_window(curwin) && bot <= curbuf->b_ml.ml_line_count) {
	redrawWinline(curwin, bot);
	}
	// Set the '[ mark.
	if (top + 1 < curbuf->b_op_start.lnum) {
	curbuf->b_op_start.lnum = top + 1;
	}
	// Set the '] mark.
	if (newsize == 0 && top + 1 > curbuf->b_op_end.lnum) {
	curbuf->b_op_end.lnum = top + 1;
	} else if (top + newsize > curbuf->b_op_end.lnum) {
	curbuf->b_op_end.lnum = top + newsize;
	}
	u_newcount += newsize;
	u_oldcount += oldsize;
	uep->ue_size = oldsize;
	uep->ue_array = newarray;
	uep->ue_bot = top + newsize + 1;
	// insert this entry in front of the new entry list
	nuep = uep->ue_next;
	uep->ue_next = newlist;
	newlist = uep;
	}
	// Ensure the '[ and '] marks are within bounds.
	if (curbuf->b_op_start.lnum > curbuf->b_ml.ml_line_count) {
	curbuf->b_op_start.lnum = curbuf->b_ml.ml_line_count;
	}
	if (curbuf->b_op_end.lnum > curbuf->b_ml.ml_line_count) {
	curbuf->b_op_end.lnum = curbuf->b_ml.ml_line_count;
	}
	// Adjust Extmarks
	ExtmarkUndoObject undo_info;
	if (undo) {
	for (int i = (int)kv_size(curhead->uh_extmark) - 1; i > -1; i--) {
	undo_info = kv_A(curhead->uh_extmark, i);
	extmark_apply_undo(undo_info, undo);
	}
	// redo
	} else {
	for (int i = 0; i < (int)kv_size(curhead->uh_extmark); i++) {
	undo_info = kv_A(curhead->uh_extmark, i);
	extmark_apply_undo(undo_info, undo);
	}
	}

Normally, changed_lines() should be called after adjusting extmarks. This order is important because the result of changed_lines() may depend on the result of on_bytes. For example, changed_lines() updates folds, and the treesitter folding shifts foldlevels in on_bytes. So if changed_lines() is called before on_bytes, the folds can be wrong. See also #26364.

Steps to reproduce

repro.vim

function Fde()
  echom 'foldexpr' v:lnum
endfunction
set foldmethod=expr foldexpr=Fde()
lua vim.api.nvim_buf_attach(0, false, {on_bytes = function() print('on_bytes') end})

1. Run

   nvim --clean
   :so repro.vim
   

   This prints foldexpr 1 to :mess
2. Type o<Esc>.
   This prints the following to :mess, in the correct order.

   on_bytes
   foldexpr 1
   foldexpr 2
   

3. Type u.
   This prints the following to :mess, in the wrong order.

   foldexpr 1
   on_bytes
   

Expected behavior

on_bytes, then foldexpr

Neovim version (nvim -v)

2ebd328

Vim (not Nvim) behaves the same?

N/A

Operating system/version

ubuntu 23.10

Terminal name/version

GNOME Terminal 3.49.92 using VTE 0.74.0 +BIDI +GNUTLS +ICU +SYSTEMD

$TERM environment variable

tmux-256color

Installation

build from repo

[tomtomjhj]

Why isn't ExtmarkUndoObject stored in each u_entry_T?