patch 9.0.0294: crash when 'cmdheight' is 0 and popup_clear() used

Problem:    Crash when 'cmdheight' is 0 and popup_clear() used.
Solution:   Reset "message_win" when the message popup is cleared.  Close the
            popup when 'cmdheight' is non-zero.  Add a screendump test.

src/popupwin.c

@@ -28,6 +28,11 @@ static poppos_entry_T poppos_entries[] = {
     {"center", POPPOS_CENTER}
 };
 
+#ifdef HAS_MESSAGE_WINDOW
+// Window used for messages when 'winheight' is zero.
+static win_T *message_win = NULL;
+#endif
+
 static void popup_adjust_position(win_T *wp);
 
 /*
@@ -2770,6 +2775,11 @@ popup_free(win_T *wp)
 	clear_cmdline = TRUE;
     win_free_popup(wp);
 
+#ifdef HAS_MESSAGE_WINDOW
+    if (wp == message_win)
+	message_win = NULL;
+#endif
+
     redraw_all_later(UPD_NOT_VALID);
     popup_mask_refresh = TRUE;
 }
@@ -4440,9 +4450,6 @@ popup_close_info(void)
 
 #if defined(HAS_MESSAGE_WINDOW) || defined(PROTO)
 
-// Window used for messages when 'winheight' is zero.
-static win_T *message_win = NULL;
-
 /*
  * Get the message window.
  * Returns NULL if something failed.
@@ -4516,6 +4523,16 @@ popup_hide_message_win(void)
 	popup_hide(message_win);
 }
 
+/*
+ * If the message window exists: close it.
+ */
+    void
+popup_close_message_win(void)
+{
+    if (message_win != NULL)
+	popup_close(message_win->w_id, TRUE);
+}
+
 #endif
 
 /*

src/proto/popupwin.pro

@@ -66,6 +66,7 @@ win_T *popup_get_message_win(void);
 void popup_show_message_win(void);
 int popup_message_win_visible(void);
 void popup_hide_message_win(void);
+void popup_close_message_win(void);
 int popup_win_closed(win_T *win);
 void popup_set_title(win_T *wp);
 void popup_update_preview_title(void);

src/testdir/dumps/Test_cmdheight_zero_1.dump

@@ -0,0 +1,6 @@
+>s+0&#ffffff0|o|m|e| |t|e|x|t| @65
+|~+0#4040ff13&| @73
+|~| @73
+|~| @73
+|~| @73
+|~| @73

src/testdir/dumps/Test_cmdheight_zero_2.dump

@@ -0,0 +1,6 @@
+|s+0&#e0e0e08|o|m|e| >t+0&#ffffff0|e|x|t| @65
+|~+0#4040ff13&| @73
+|~| @73
+|~| @73
+|~| @73
+|~| @73

src/testdir/dumps/Test_cmdheight_zero_3.dump

@@ -0,0 +1,6 @@
+|s+0&#ffffff0|o|m|e| >t|e|x|t| @65
+|~+0#4040ff13&| @73
+|~| @73
+|~| @73
+|═+0#e000002&@74
+|m|e|s@1|a|g|e| |w|i|n|d|o|w| @60

src/testdir/test_messages.vim

@@ -471,4 +471,32 @@ func Test_cmdheight_zero()
   redraw
 endfunc
 
+func Test_cmdheight_zero_dump()
+  CheckScreendump
+
+  let lines =<< trim END
+      set cmdheight=0
+      set showmode
+      call setline(1, 'some text')
+  END
+  call writefile(lines, 'XtestCmdheight')
+  let buf = RunVimInTerminal('-S XtestCmdheight', #{rows: 6})
+  " The "-- INSERT --" indicator should not be visible.
+  call term_sendkeys(buf, "i")
+  call VerifyScreenDump(buf, 'Test_cmdheight_zero_1', {})
+
+  " The "-- VISUAL --" indicator should not be visible.
+  call term_sendkeys(buf, "\<Esc>vw")
+  call VerifyScreenDump(buf, 'Test_cmdheight_zero_2', {})
+
+  " Echo'd text is in a popup window
+  call term_sendkeys(buf, "\<Esc>:echo 'message window'\<CR>")
+  call VerifyScreenDump(buf, 'Test_cmdheight_zero_3', {})
+
+  " clean up
+  call StopVimInTerminal(buf)
+  call delete('XtestCmdheight')
+endfunc
+
+
 " vim: shiftwidth=2 sts=2 expandtab

src/version.c

@@ -707,6 +707,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    294,
 /**/
     293,
 /**/

src/window.c

@@ -6603,6 +6603,11 @@ command_height(void)
     // Recompute window positions.
     if (frp != lastwin->w_frame)
 	(void)win_comp_pos();
+
+#ifdef HAS_MESSAGE_WINDOW
+    if (p_ch > 0)
+	popup_close_message_win();
+#endif
 }
 
 /*