vim-patch:8.2.1059: crash when using :tabonly in an autocommand

Problem:    Crash when using :tabonly in an autocommand. (Yegappan Lakshmanan)
Solution:   Do not allow the autocommand window to be closed.
cf8441704d

E813 error message does not mention 'popup' window
because Neovim floating window are regular windows, unlike Vim popups.

https://github.com/neovim/neovim/pull/14532#discussion_r631731829

src/nvim/ex_docmd.c

@@ -6520,6 +6520,12 @@ ex_win_close(
   int need_hide;
   buf_T       *buf = win->w_buffer;
 
+  // Never close the autocommand window.
+  if (win == aucmd_win) {
+    EMSG(_(e_autocmd_close));
+    return;
+  }
+
   need_hide = (bufIsChanged(buf) && buf->b_nwindows <= 1);
   if (need_hide && !buf_hide(buf) && !forceit) {
     if ((p_confirm || cmdmod.confirm) && p_write) {

src/nvim/globals.h

@@ -987,6 +987,8 @@ EXTERN char_u e_dirnotf[] INIT(= N_(
     "E919: Directory not found in '%s': \"%s\""));
 EXTERN char_u e_au_recursive[] INIT(= N_(
     "E952: Autocommand caused recursive behavior"));
+EXTERN char_u e_autocmd_close[] INIT(= N_(
+    "E813: Cannot close autocmd window"));
 EXTERN char_u e_unsupportedoption[] INIT(= N_("E519: Option not supported"));
 EXTERN char_u e_fnametoolong[] INIT(= N_("E856: Filename too long"));
 EXTERN char_u e_float_as_string[] INIT(= N_("E806: using Float as a String"));

src/nvim/testdir/test_autocmd.vim

@@ -1949,6 +1949,26 @@ func Test_autocmd_window()
   %bw!
 endfunc
 
+" Test for trying to close the tab that has the temporary window for exeucing
+" an autocmd.
+func Test_close_autocmd_tab()
+  edit one.txt
+  tabnew two.txt
+   augroup aucmd_win_test
+    au!
+    au BufEnter * if expand('<afile>') == 'one.txt' | tabfirst | tabonly | endif
+  augroup END
+
+  call assert_fails('doautoall BufEnter', 'E813:')
+
+  tabonly
+  augroup aucmd_win_test
+    au!
+  augroup END
+  augroup! aucmd_win_test
+  %bwipe!
+endfunc
+
 func Test_autocmd_closes_window()
   au BufNew,BufWinLeave * e %e
   file yyy

src/nvim/window.c

@@ -2286,7 +2286,7 @@ int win_close(win_T *win, bool free_buf)
     return FAIL;     // window is already being closed
   }
   if (win == aucmd_win) {
-    EMSG(_("E813: Cannot close autocmd window"));
+    EMSG(_(e_autocmd_close));
     return FAIL;
   }
   if ((firstwin == aucmd_win || lastwin == aucmd_win) && one_window()) {