patch 9.0.0550: crash when closing a tabpage and buffer is NULL

Problem:    Crash when closing a tabpage and buffer is NULL.
Solution:   Adjust how autocommands are triggered when closing a window.
            (closes #11198, closes #11197)

src/ex_docmd.c

@@ -6304,7 +6304,6 @@ tabpage_close_other(tabpage_T *tp, int forceit)
 {
     int		done = 0;
     win_T	*wp;
-    int		h = tabline_height();
 
     // Limit to 1000 windows, autocommands may add a window while we close
     // one.  OK, so I'm paranoid...
@@ -6320,10 +6319,6 @@ tabpage_close_other(tabpage_T *tp, int forceit)
     }
 
     apply_autocmds(EVENT_TABCLOSED, NULL, NULL, FALSE, curbuf);
-
-    redraw_tabline = TRUE;
-    if (h != tabline_height())
-	shell_new_rows();
 }
 
 /*

src/testdir/test_autocmd.vim

@@ -515,6 +515,26 @@ func Test_WinClosed_throws_with_tabs()
   augroup! test-WinClosed
 endfunc
 
+" This used to trigger WinClosed twice for the same window, and the window's
+" buffer was NULL in the second autocommand.
+func Test_WinClosed_switch_tab()
+  edit Xa
+  split Xb
+  split Xc
+  tab split
+  new
+  augroup test-WinClosed
+    autocmd WinClosed * tabprev | bwipe!
+  augroup END
+  close
+  " Check that the tabline has been fully removed
+  call assert_equal([1, 1], win_screenpos(0))
+
+  autocmd! test-WinClosed
+  augroup! test-WinClosed
+  %bwipe!
+endfunc
+
 func s:AddAnAutocmd()
   augroup vimBarTest
     au BufReadCmd * echo 'hello'

src/version.c

@@ -699,6 +699,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    550,
 /**/
     549,
 /**/

src/window.c

@@ -2340,7 +2340,6 @@ close_windows(
 {
     win_T	*wp;
     tabpage_T   *tp, *nexttp;
-    int		h = tabline_height();
     int		count = tabpage_index(NULL);
 
     ++RedrawingDisabled;
@@ -2384,10 +2383,6 @@ close_windows(
 
     if (count != tabpage_index(NULL))
 	apply_autocmds(EVENT_TABCLOSED, NULL, NULL, FALSE, curbuf);
-
-    redraw_tabline = TRUE;
-    if (h != tabline_height())
-	shell_new_rows();
 }
 
 /*
@@ -2446,18 +2441,11 @@ close_last_window_tabpage(
 	 * that below.
 	 */
 	goto_tabpage_tp(alt_tabpage(), FALSE, TRUE);
-	redraw_tabline = TRUE;
 
 	// Safety check: Autocommands may have closed the window when jumping
 	// to the other tab page.
 	if (valid_tabpage(prev_curtab) && prev_curtab->tp_firstwin == win)
-	{
-	    int	    h = tabline_height();
-
 	    win_close_othertab(win, free_buf, prev_curtab);
-	    if (h != tabline_height())
-		shell_new_rows();
-	}
 #ifdef FEAT_JOB_CHANNEL
 	entering_window(curwin);
 #endif
@@ -2656,7 +2644,10 @@ win_close(win_T *win, int free_buf)
 						      && win->w_buffer == NULL)
     {
 	// Need to close the window anyway, since the buffer is NULL.
+	// Don't trigger autocmds with a NULL buffer.
+	block_autocmds();
 	win_close_othertab(win, FALSE, prev_curtab);
+	unblock_autocmds();
 	return FAIL;
     }
 
@@ -2907,6 +2898,8 @@ win_close_othertab(win_T *win, int free_buf, tabpage_T *tp)
     // When closing the last window in a tab page remove the tab page.
     if (tp->tp_firstwin == tp->tp_lastwin)
     {
+	int	h = tabline_height();
+
 	if (tp == first_tabpage)
 	    first_tabpage = tp->tp_next;
 	else
@@ -2922,6 +2915,9 @@ win_close_othertab(win_T *win, int free_buf, tabpage_T *tp)
 	    ptp->tp_next = tp->tp_next;
 	}
 	free_tp = TRUE;
+	redraw_tabline = TRUE;
+	if (h != tabline_height())
+	    shell_new_rows();
     }
 
     // Free the memory used for the window.