patch 9.1.1571: CmdlineChanged triggered to often

Problem:  The CmdlineChanged event was firing unnecessarily, even when
          the command line's content hadn't actually changed.

Solution: I've added a check to compare the command-line buffer's state
          before and after key processing. The `CmdlineChanged` event
          now only triggers if the buffer's contents are genuinely
          different (Girish Palya).

closes: #17803

Signed-off-by: Girish Palya <girishji@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>

src/ex_getln.c

@@ -1633,7 +1633,6 @@ getcmdline_int(
     int		res;
     int		save_msg_scroll = msg_scroll;
     int		save_State = State;	// remember State when called
-    int		prev_cmdpos = -1;
     int		some_key_typed = FALSE;	// one of the keys was typed
     // mouse drag and release events are ignored, unless they are
     // preceded with a mouse down event
@@ -1649,6 +1648,7 @@ getcmdline_int(
     int		cmdline_type;
     int		wild_type = 0;
     int		event_cmdlineleavepre_triggered = FALSE;
+    char_u	*prev_cmdbuff = NULL;
 
     // one recursion level deeper
     ++depth;
@@ -1820,6 +1820,7 @@ getcmdline_int(
     {
 	int trigger_cmdlinechanged = TRUE;
 	int end_wildmenu;
+	int prev_cmdpos = ccline.cmdpos;
 
 	redir_off = TRUE;	// Don't redirect the typed command.
 				// Repeated, because a ":redir" inside
@@ -1836,6 +1837,13 @@ getcmdline_int(
 	// Trigger SafeState if nothing is pending.
 	may_trigger_safestate(xpc.xp_numfiles <= 0);
 
+	if (ccline.cmdbuff != NULL)
+	{
+	    prev_cmdbuff = vim_strnsave(ccline.cmdbuff, ccline.cmdpos);
+	    if (prev_cmdbuff == NULL)
+		goto returncmd;
+	}
+
 	// Get a character.  Ignore K_IGNORE and K_NOP, they should not do
 	// anything, such as stop completion.
 	do
@@ -2566,7 +2574,10 @@ cmdline_not_changed:
 
 #ifdef FEAT_SEARCH_EXTRA
 	if (!is_state.incsearch_postponed)
+	{
+	    VIM_CLEAR(prev_cmdbuff);
 	    continue;
+	}
 #endif
 
 cmdline_changed:
@@ -2578,15 +2589,17 @@ cmdline_changed:
 	    may_do_incsearch_highlighting(firstc, count, &is_state);
 #endif
 	// Trigger CmdlineChanged autocommands.
-	if (trigger_cmdlinechanged)
+	if (trigger_cmdlinechanged
+		&& (ccline.cmdpos != prev_cmdpos
+		    || (prev_cmdbuff != NULL && STRNCMP(prev_cmdbuff,
+			    ccline.cmdbuff, prev_cmdpos) != 0)))
 	    trigger_cmd_autocmd(cmdline_type, EVENT_CMDLINECHANGED);
 
+	VIM_CLEAR(prev_cmdbuff);
+
 	// Trigger CursorMovedC autocommands.
 	if (ccline.cmdpos != prev_cmdpos)
-	{
 	    trigger_cmd_autocmd(cmdline_type, EVENT_CURSORMOVEDC);
-	    prev_cmdpos = ccline.cmdpos;
-	}
 
 #ifdef FEAT_RIGHTLEFT
 	if (cmdmsg_rl
@@ -2695,6 +2708,8 @@ theend:
 	    restore_cmdline(&save_ccline);
 	else
 	    ccline.cmdbuff = NULL;
+
+	vim_free(prev_cmdbuff);
 	return p;
     }
 }

src/testdir/test_cmdline.vim

@@ -4691,4 +4691,53 @@ func Test_pum_scroll_noselect()
   call StopVimInTerminal(buf)
 endfunc
 
+" CmdlineChanged shouldn't trigger if command-line text is unchanged
+func Test_cmdline_changed()
+  let g:cmdchg_count = 0
+  let g:cmdprefix = ''
+  augroup test_CmdlineAugrp | autocmd!
+    autocmd CmdlineChanged * if getcmdline() =~ g:cmdprefix | let g:cmdchg_count += 1 | endif
+  augroup END
+
+  new
+  set wildmenu
+  set wildmode=full
+
+  let g:cmdprefix = 'echomsg'
+  let g:cmdchg_count = 0
+  call feedkeys(":echomsg\<Tab>", "tx")
+  call assert_equal(1, g:cmdchg_count) " once only for 'g', not again for <Tab>
+
+  let g:cmdchg_count = 0
+  let g:cmdprefix = 'echo'
+  call feedkeys(":ech\<Tab>", "tx")
+  call assert_equal(1, g:cmdchg_count) " (once for 'h' and) once for 'o'
+
+  set wildmode=noselect,full
+  let g:cmdchg_count = 0
+  let g:cmdprefix = 'ech'
+  call feedkeys(":ech\<Tab>", "tx")
+  call assert_equal(1, g:cmdchg_count) " once for 'h', not again for <tab>
+
+  command! -nargs=+ -complete=custom,TestComplete Test echo
+
+  func TestComplete(arglead, cmdline, cursorpos)
+    return "AbC"
+  endfunc
+
+  set wildoptions=fuzzy wildmode=full
+  let g:cmdchg_count = 0
+  let g:cmdprefix = 'Test \(AbC\|abc\)'
+  call feedkeys(":Test abc\<Tab>", "tx")
+  call assert_equal(2, g:cmdchg_count) " once for 'c', again for 'AbC'
+
+  bw!
+  set wildmode& wildmenu& wildoptions&
+  augroup test_CmdlineAugrp | autocmd! | augroup END
+  unlet g:cmdchg_count
+  unlet g:cmdprefix
+  delfunc TestComplete
+  delcommand Test
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab

src/version.c

@@ -719,6 +719,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1571,
 /**/
     1570,
 /**/