vim-patch:8.2.2433: opening cmdline window gives error in BufLeave autocommand

Problem:    Opening cmdline window gives error in BufLeave autocommand.
Solution:   Reset cmdwin_type when triggering the autocommand.
b63f3ca66d

src/nvim/ex_cmds.c

@@ -2434,6 +2434,11 @@ int do_ecmd(
      * is returned by buflist_new(), nothing to do here.
      */
     if (buf != curbuf) {
+      const int save_cmdwin_type = cmdwin_type;
+
+      // BufLeave applies to the old buffer.
+      cmdwin_type = 0;
+
       /*
        * Be careful: The autocommands may delete any buffer and change
        * the current buffer.
@@ -2449,6 +2454,7 @@ int do_ecmd(
       }
       set_bufref(&au_new_curbuf, buf);
       apply_autocmds(EVENT_BUFLEAVE, NULL, NULL, false, curbuf);
+      cmdwin_type = save_cmdwin_type;
       if (!bufref_valid(&au_new_curbuf)) {
         // New buffer has been deleted.
         delbuf_msg(new_name);  // Frees new_name.

src/nvim/testdir/test_cmdline.vim

@@ -1005,6 +1005,25 @@ func Test_buffers_lastused()
   bwipeout bufc
 endfunc
 
+" Test for CmdwinEnter autocmd
+func Test_cmdwin_autocmd()
+  CheckFeature cmdwin
+
+  augroup CmdWin
+    au!
+    autocmd BufLeave * if &buftype == '' | update | endif
+    autocmd CmdwinEnter * startinsert
+  augroup END
+
+  call assert_fails('call feedkeys("q:xyz\<CR>", "xt")', 'E492:')
+  call assert_equal('xyz', @:)
+
+  augroup CmdWin
+    au!
+  augroup END
+  augroup! CmdWin
+endfunc
+
 func Test_cmdlineclear_tabenter()
   " See test/functional/legacy/cmdline_spec.lua
   CheckScreendump