feat: implement BufModified autocmd

src/nvim/auevents.lua

@@ -7,6 +7,7 @@ return {
     'BufFilePre',             -- before renaming a buffer
     'BufHidden',              -- just after buffer becomes hidden
     'BufLeave',               -- before leaving a buffer
+    'BufModified',            -- after the 'modified' state of a buffer changes
     'BufNew',                 -- after creating any buffer
     'BufNewFile',             -- when creating a buffer for a new file
     'BufReadCmd',             -- read buffer using command
@@ -124,6 +125,7 @@ return {
   -- List of nvim-specific events or aliases for the purpose of generating
   -- syntax file
   nvim_specific = {
+    BufModified=true,
     DirChanged=true,
     Signal=true,
     TabClosed=true,

src/nvim/buffer_defs.h

@@ -541,6 +541,8 @@ 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_notified;      // if the BufModified autocmd has been triggered
+                                // since the last time b_changed was modified
 
   /// Change-identifier incremented for each change, including undo.
   ///

src/nvim/change.c

@@ -129,6 +129,7 @@ void changed(void)
 void changed_internal(void)
 {
   curbuf->b_changed = true;
+  curbuf->b_changed_notified = false;
   ml_setflags(curbuf);
   check_status(curbuf);
   redraw_tabline = true;
@@ -502,6 +503,7 @@ void unchanged(buf_T *buf, int ff, bool always_inc_changedtick)
 {
   if (buf->b_changed || (ff && file_ff_differs(buf, false))) {
     buf->b_changed = false;
+    buf->b_changed_notified = false;
     ml_setflags(buf);
     if (ff) {
       save_file_ff(buf);

src/nvim/edit.c

@@ -1488,6 +1488,14 @@ static void ins_redraw(
     do_autocmd_winscrolled(curwin);
   }
 
+  // Trigger BufModified if b_changed_notified is false.
+  if (ready && has_event(EVENT_BUFMODIFIED)
+      && curbuf->b_changed_notified == false
+      && !pum_visible()) {
+    apply_autocmds(EVENT_BUFMODIFIED, NULL, NULL, false, curbuf);
+    curbuf->b_changed_notified = true;
+  }
+
   if (curwin->w_p_cole > 0 && conceal_cursor_line(curwin)
       && conceal_cursor_moved) {
     redrawWinline(curwin, curwin->w_cursor.lnum);

src/nvim/normal.c

@@ -1229,6 +1229,16 @@ static void normal_check_text_changed(NormalState *s)
   }
 }
 
+static void normal_check_buffer_modified(NormalState *s)
+{
+  // Trigger BufModified if b_modified changed
+  if (!finish_op && has_event(EVENT_BUFMODIFIED)
+      && curbuf->b_changed_notified == false) {
+    apply_autocmds(EVENT_BUFMODIFIED, NULL, NULL, false, curbuf);
+    curbuf->b_changed_notified = true;
+  }
+}
+
 static void normal_check_folds(NormalState *s)
 {
   // Include a closed fold completely in the Visual area.
@@ -1336,6 +1346,7 @@ 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);
 
     // Updating diffs from changed() does not always work properly,
     // esp. updating folds.  Do an update just before redrawing if