patch 9.2.0340: pum_redraw() may cause flicker

Problem:  pum_redraw() may cause flicker
Solution: Wrap pum_redraw() in synchronized output to avoid flicker
          (Yasuhiro Matsumoto)

closes: #19955

Signed-off-by: Yasuhiro Matsumoto <mattn.jp@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>

src/popupmenu.c

@@ -953,6 +953,10 @@ pum_redraw(void)
     // Use current window for highlight overrides when using 'winhighlight'
     override_success = push_highlight_overrides(curwin->w_hl, curwin->w_hl_len);
 
+    // Batch the underlying screen update and the pum drawing into a single
+    // synchronized output frame to avoid flicker.
+    term_set_sync_output(TERM_SYNC_OUTPUT_ENABLE);
+
     hlf_T	hlfsNorm[3];
     hlf_T	hlfsSel[3];
     // "word"/"abbr"
@@ -1187,6 +1191,8 @@ pum_redraw(void)
 
     if (override_success)
 	pop_highlight_overrides();
+
+    term_set_sync_output(TERM_SYNC_OUTPUT_DISABLE);
 }
 
 #if defined(FEAT_PROP_POPUP) && defined(FEAT_QUICKFIX)

src/version.c

@@ -734,6 +734,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    340,
 /**/
     339,
 /**/