fix(redraw): handle switching to a tabpage with larger p_ch value

src/nvim/window.c

@@ -4343,6 +4343,11 @@ static void enter_tabpage(tabpage_T *tp, buf_T *old_curbuf, bool trigger_enter_a
   // Use the stored value of p_ch, so that it can be different for each tab page.
   if (p_ch != curtab->tp_ch_used) {
     clear_cmdline = true;
+    if (msg_grid.chars && p_ch < curtab->tp_ch_used) {
+      // TODO(bfredl): a bit expensive, should be enough to invalidate the
+      // region between the old and the new p_ch.
+      grid_invalidate(&msg_grid);
+    }
   }
   p_ch = curtab->tp_ch_used;
 

test/functional/legacy/cmdline_spec.lua

@@ -19,8 +19,6 @@ describe('cmdline', function()
       [3] = {reverse = true};
       [4] = {bold = true, foreground = Screen.colors.Blue1};
     }
-    -- TODO(bfredl): redraw with tabs is severly broken. fix it
-    feed_command [[ set display-=msgsep ]]
 
     feed_command([[call setline(1, range(30))]])
     screen:expect([[
@@ -61,7 +59,7 @@ describe('cmdline', function()
       {4:~                             }|
                                     |
                                     |
-      :tabnew                       |
+                                    |
     ]]}
 
     feed [[gt]]