feat(events)!: support Optionset modified, drop BufModifiedSet #35610

Problem:
BufModifiedSet autocmd only triggered for current buffer during
redraw, causing delayed events when :wa writes non-current buffers.

Solution:
- Use the aucmd_defer approach to implement `Optionset modified`.
- Drop BufModifiedSet.

runtime/doc/autocmd.txt

@@ -292,10 +292,6 @@ BufLeave			Before leaving to another buffer.  Also when
 
 				Not used for ":qa" or ":q" when exiting Vim.
 
-							*BufModifiedSet*
-BufModifiedSet			After the `'modified'` value of a buffer has
-				been changed. Special-case of |OptionSet|.
-
 							*BufNew*
 BufNew				After creating a new buffer (except during
 				startup, see |VimEnter|) or renaming an
@@ -926,9 +922,9 @@ OptionSet			After setting an option (except during
 				always use |:noautocmd| to prevent triggering
 				OptionSet.
 
-				Note: Not triggered by the 'modified' option;
-				the |BufModifiedSet| event may be used to
-				handle that.
+				Note: The 'modified' option triggers
+				|OptionSet| deferred to the next event-loop
+				tick, even when set via |:set|.
 
 				Non-recursive: |:set| in the autocommand does
 				not trigger OptionSet again.

runtime/doc/deprecated.txt

@@ -24,6 +24,9 @@ API
   • |nvim_exec_autocmds()|
   • |nvim_clear_autocmds()|
 
+EVENTS
+• *BufModifiedSet*	Use |OptionSet| with pattern "modified" instead.
+
 ------------------------------------------------------------------------------
 DEPRECATED IN 0.12					*deprecated-0.12*
 

runtime/doc/news.txt

@@ -81,6 +81,8 @@ EDITOR
 
 EVENTS
 
+• |BufModifiedSet| has been removed. Use the |OptionSet| event with pattern
+  "modified" instead.
 • todo
 
 LSP

runtime/doc/vim_diff.txt

@@ -334,7 +334,8 @@ Editor:
 
 Events (autocommands):
 - Fixed inconsistent behavior in execution of nested autocommands #23368
-- |BufModifiedSet|
+- |OptionSet| is now fired for 'modified' when writing a file,
+  undoing changes, or using |:set| modified.
 - |Progress|
 - |RecordingEnter|
 - |RecordingLeave|

runtime/lua/vim/_meta/api_keysets.gen.lua

@@ -88,7 +88,6 @@ error('Cannot require a meta file')
 --- |'BufFilePre'
 --- |'BufHidden'
 --- |'BufLeave'
---- |'BufModifiedSet'
 --- |'BufNew'
 --- |'BufNewFile'
 --- |'BufRead'

src/nvim/auevents.lua

@@ -10,7 +10,6 @@ return {
     BufFilePre = true, -- before renaming a buffer
     BufHidden = true, -- just after buffer becomes hidden
     BufLeave = true, -- before leaving a buffer
-    BufModifiedSet = true, -- after the 'modified' state of a buffer changes
     BufNew = true, -- after creating any buffer
     BufNewFile = true, -- when creating a buffer for a new file
     BufReadCmd = true, -- read buffer using command
@@ -157,7 +156,6 @@ return {
   --- @type table<string,true>
   --- List of Nvim-specific events or aliases for generating syntax file.
   nvim_specific = {
-    BufModifiedSet = true,
     DiagnosticChanged = true,
     LspAttach = true,
     LspDetach = true,

src/nvim/autocmd.c

@@ -1551,6 +1551,35 @@ static void deferred_event(void **argv)
   xfree(e);
 }
 
+static void deferred_optionset_modified(void **argv)
+{
+  Error err = ERROR_INIT;
+  buf_T *buf = find_buffer_by_handle((handle_T)(uintptr_t)argv[0], &err);
+  api_clear_error(&err);
+  if (buf) {
+    bool new_val = (bool)(uintptr_t)argv[1];
+    OptVal old = BOOLEAN_OPTVAL(!new_val);
+    OptVal new = BOOLEAN_OPTVAL(new_val);
+    aco_save_T aco;
+    aucmd_prepbuf(&aco, buf);
+    apply_optionset_autocmd_now(kOptModified, OPT_LOCAL, old, old, old, new, NULL);
+    aucmd_restbuf(&aco);
+  }
+}
+
+/// Special case of aucmd_defer for `OptionSet modified`.
+void aucmd_defer_modified(buf_T *buf, bool new_val)
+{
+  if (!has_event(EVENT_OPTIONSET)
+      || (bt_nofile(buf) && !buf->b_p_bl)
+      || *get_vim_var_str(VV_OPTION_TYPE) != NUL) {
+    return;
+  }
+  multiqueue_put(deferred_events, deferred_optionset_modified,
+                 (void *)(uintptr_t)buf->handle,
+                 (void *)(uintptr_t)new_val);
+}
+
 /// Execute autocommands for "event" and file name "fname".
 ///
 /// @param event event that occurred

src/nvim/buffer_defs.h

@@ -404,9 +404,6 @@ struct file_buffer {
 
   int b_changed;                // 'modified': Set to true if something in the
                                 // file has been changed and not written out.
-  bool b_changed_invalid;       // Set if BufModified autocmd has not been
-                                // triggered since the last time b_changed was
-                                // modified.
 
   /// Change-identifier incremented for each change, including undo.
   ///

src/nvim/change.c

@@ -150,12 +150,15 @@ void changed(buf_T *buf)
 /// Also used for recovery.
 void changed_internal(buf_T *buf)
 {
+  bool was_changed = buf->b_changed;
   buf->b_changed = true;
-  buf->b_changed_invalid = true;
   ml_setflags(buf);
   redraw_buf_status_later(buf);
   redraw_tabline = true;
   need_maketitle = true;  // set window title later
+  if (!was_changed) {
+    aucmd_defer_modified(buf, true);
+  }
 }
 
 /// Invalidate a window's w_valid flags and w_lines[] entries after changing lines.
@@ -606,8 +609,8 @@ void changed_lines(buf_T *buf, linenr_T lnum, colnr_T col, linenr_T lnume, linen
 void unchanged(buf_T *buf, bool ff, bool always_inc_changedtick)
 {
   if (buf->b_changed || (ff && file_ff_differs(buf, false))) {
+    bool was_changed = buf->b_changed;
     buf->b_changed = false;
-    buf->b_changed_invalid = true;
     ml_setflags(buf);
     if (ff) {
       save_file_ff(buf);
@@ -616,6 +619,9 @@ void unchanged(buf_T *buf, bool ff, bool always_inc_changedtick)
     redraw_tabline = true;
     need_maketitle = true;  // set window title later
     buf_inc_changedtick(buf);
+    if (was_changed) {
+      aucmd_defer_modified(buf, false);
+    }
   } else if (always_inc_changedtick) {
     buf_inc_changedtick(buf);
   }

src/nvim/edit.c

@@ -1456,18 +1456,8 @@ void ins_redraw(bool ready)
     may_trigger_win_scrolled_resized();
   }
 
-  // Trigger BufModified if b_changed_invalid is set.
-  if (ready && has_event(EVENT_BUFMODIFIEDSET)
-      && curbuf->b_changed_invalid == true
-      && !pum_visible()) {
-    apply_autocmds(EVENT_BUFMODIFIEDSET, NULL, NULL, false, curbuf);
-    curbuf->b_changed_invalid = false;
-  }
-
   // Trigger SafeState if nothing is pending.
-  may_trigger_safestate(ready
-                        && !ins_compl_active()
-                        && !pum_visible());
+  may_trigger_safestate(ready && !ins_compl_active() && !pum_visible());
 
   pum_check_clear();
   show_cursor_info_later(false);

src/nvim/normal.c

@@ -1326,16 +1326,6 @@ static void normal_check_text_changed(NormalState *s)
   }
 }
 
-static void normal_check_buffer_modified(NormalState *s)
-{
-  // Trigger BufModified if 'modified' changed.
-  if (!finish_op && has_event(EVENT_BUFMODIFIEDSET)
-      && curbuf->b_changed_invalid == true) {
-    apply_autocmds(EVENT_BUFMODIFIEDSET, NULL, NULL, false, curbuf);
-    curbuf->b_changed_invalid = false;
-  }
-}
-
 /// If nothing is pending and we are going to wait for the user to
 /// type a character, trigger SafeState.
 static void normal_check_safe_state(NormalState *s)
@@ -1451,7 +1441,6 @@ static int normal_check(VimState *state)
     normal_check_cursor_moved(s);
     normal_check_text_changed(s);
     normal_check_window_scrolled(s);
-    normal_check_buffer_modified(s);
     normal_check_safe_state(s);
 
     // Updating diffs from changed() does not always work properly,

src/nvim/option.c

@@ -2060,9 +2060,9 @@ void set_option_sctx(OptIndex opt_idx, int opt_flags, sctx_T script_ctx)
   }
 }
 
-/// Apply the OptionSet autocommand.
-static void apply_optionset_autocmd(OptIndex opt_idx, int opt_flags, OptVal oldval, OptVal oldval_g,
-                                    OptVal oldval_l, OptVal newval, const char *errmsg)
+/// Fire OptionSet autocmd directly (called from deferred context, bypasses defer logic).
+void apply_optionset_autocmd_now(OptIndex opt_idx, int opt_flags, OptVal oldval, OptVal oldval_g,
+                                 OptVal oldval_l, OptVal newval, const char *errmsg)
 {
   // Don't do this while starting up, failure or recursively.
   if (starting || errmsg != NULL || *get_vim_var_str(VV_OPTION_TYPE) != NUL) {
@@ -2101,6 +2101,20 @@ static void apply_optionset_autocmd(OptIndex opt_idx, int opt_flags, OptVal oldv
   reset_v_option_vars();
 }
 
+/// For 'modified', the event is deferred.
+static void apply_optionset_autocmd(OptIndex opt_idx, int opt_flags, OptVal oldval, OptVal oldval_g,
+                                    OptVal oldval_l, OptVal newval, const char *errmsg)
+{
+  if (starting || errmsg != NULL) {
+    return;
+  }
+  if (opt_idx == kOptModified) {
+    aucmd_defer_modified(curbuf, newval.data.boolean);
+    return;
+  }
+  apply_optionset_autocmd_now(opt_idx, opt_flags, oldval, oldval_g, oldval_l, newval, errmsg);
+}
+
 /// Process the updated 'arabic' option value.
 static const char *did_set_arabic(optset_T *args)
 {

test/functional/autocmd/autocmd_spec.lua

@@ -20,6 +20,7 @@ local command = n.command
 local exec_lua = n.exec_lua
 local retry = t.retry
 local source = n.source
+local request = n.request
 
 describe('autocmd', function()
   before_each(clear)
@@ -856,4 +857,52 @@ describe('autocmd', function()
       fn.execute('autocmd User ,,,there,is,,a,fly,,')
     )
   end)
+
+  describe('OptionSet modified', function()
+    before_each(clear)
+
+    it('is triggered when modified and un-modified', function()
+      source([[
+      let g:modified = 0
+      autocmd OptionSet modified let g:modified += 1
+      ]])
+      request('nvim_command', [[normal! aa\<Esc>]])
+      eq(1, eval('g:modified'))
+      request('nvim_command', [[normal! u]])
+      eq(2, eval('g:modified'))
+    end)
+
+    it('triggers when writes non-current buffer #32817', function()
+      source([[
+      let g:modified = 0
+      let g:second_trigger_buf = 0
+      autocmd OptionSet modified let g:modified += 1 | if g:modified == 2 | let g:second_trigger_buf = bufnr() | endif
+      ]])
+      request('nvim_command', [[edit test_a | badd test_b]])
+      request('nvim_command', [[normal! aa\<Esc>]])
+      request('nvim_command', [[let g:buf_a = bufnr()]])
+      request('nvim_command', [[bn]])
+      request('nvim_command', [[wa]])
+      os.remove('test_a')
+      eq({ 2, true }, { eval('g:modified'), eval('g:buf_a') == eval('g:second_trigger_buf') })
+    end)
+
+    it('OptionSet triggers correctly when modified changes', function()
+      command([[
+        autocmd OptionSet modified call add(g:messages, string(!!v:option_old) . ' -> ' . string(!!v:option_new) . ' - actual: ' . &modified)
+      ]])
+      command('let g:messages = []')
+      local fname = t.tmpname()
+      command('new ' .. fname)
+      command("call setline(1, 'hi')")
+      command('write')
+      command('set modified')
+      eq({
+        '0 -> 1 - actual: 1',
+        '1 -> 0 - actual: 0',
+        '0 -> 1 - actual: 1',
+      }, eval('g:messages'))
+      os.remove(fname)
+    end)
+  end)
 end)

test/functional/autocmd/bufmodifiedset_spec.lua

@@ -1,23 +0,0 @@
-local t = require('test.testutil')
-local n = require('test.functional.testnvim')()
-
-local clear = n.clear
-local eq = t.eq
-local eval = n.eval
-local source = n.source
-local request = n.request
-
-describe('BufModified', function()
-  before_each(clear)
-
-  it('is triggered when modified and un-modified', function()
-    source([[
-    let g:modified = 0
-    autocmd BufModifiedSet * let g:modified += 1
-    ]])
-    request('nvim_command', [[normal! aa\<Esc>]])
-    eq(1, eval('g:modified'))
-    request('nvim_command', [[normal! u]])
-    eq(2, eval('g:modified'))
-  end)
-end)

test/functional/terminal/buffer_spec.lua

@@ -1423,12 +1423,14 @@ describe(':terminal buffer', function()
   end)
 
   it('does not allow OptionSet or b:term_title watcher to delete buffer', function()
-    local au = api.nvim_create_autocmd('OptionSet', { command = 'bwipeout!' })
-    local chan = api.nvim_open_term(0, {})
+    local chan = exec_lua([[
+      local au = vim.api.nvim_create_autocmd('OptionSet', { command = 'bwipeout!' })
+      local chan = vim.api.nvim_open_term(0, {})
+      vim.api.nvim_del_autocmd(au)
+      return chan
+    ]])
     matches('^E937: ', api.nvim_get_vvar('errmsg'))
-    api.nvim_del_autocmd(au)
     api.nvim_set_vvar('errmsg', '')
-
     api.nvim_chan_send(chan, '\027]2;SOME_TITLE\007')
     eq('SOME_TITLE', api.nvim_buf_get_var(0, 'term_title'))
     command([[call dictwatcheradd(b:, 'term_title', {-> execute('bwipe!')})]])