vim-patch:9.1.0048: Abort opening cmdwin if autocmds screw things up

Problem:  Autocmds triggered from opening the cmdwin (in win_split and
          do_ecmd) can cause issues such as E199, as the current checks
          are insufficient.

Solution: Commands executed from the cmdwin apply to the old curwin/buf,
          so they should be kept in a "suspended" state; abort if
          they've changed. Also abort if cmdwin/buf was tampered with,
          and check that curwin is correct. Try to clean up the cmdwin
          buffer (only if hidden and non-current to simplify things; the
          same approach is used when closing cmdwin normally), and add a
          beep. (Sean Dewar)

Rename the old Test_cmdwin_interrupted() like in the patch (can be moved to
test_cmdwin.vim when v9.0.0027 is ported).
Move the error message to `e_active_window_or_buffer_changed_or_deleted`.

43b395ec2e

src/nvim/ex_getln.c

@@ -219,6 +219,9 @@ static int cedit_key = -1;  ///< key value of 'cedit' option
 static handle_T cmdpreview_bufnr = 0;
 static int cmdpreview_ns = 0;
 
+static const char e_active_window_or_buffer_changed_or_deleted[]
+  = N_("E199: Active window or buffer changed or deleted");
+
 static void save_viewstate(win_T *wp, viewstate_T *vs)
   FUNC_ATTR_NONNULL_ALL
 {
@@ -4323,6 +4326,14 @@ static int open_cmdwin(void)
     ga_clear(&winsizes);
     return K_IGNORE;
   }
+  // win_split() autocommands may have messed with the old window or buffer.
+  // Treat it as abandoning this command-line.
+  if (!win_valid(old_curwin) || curwin == old_curwin || !bufref_valid(&old_curbuf)
+      || old_curwin->w_buffer != old_curbuf.br_buf) {
+    beep_flush();
+    ga_clear(&winsizes);
+    return Ctrl_C;
+  }
   // Don't let quitting the More prompt make this fail.
   got_int = false;
 
@@ -4332,14 +4343,29 @@ static int open_cmdwin(void)
   cmdwin_win = curwin;
   cmdwin_old_curwin = old_curwin;
 
-  // Create empty command-line buffer.
-  if (buf_open_scratch(0, _("[Command Line]")) == FAIL) {
-    // Some autocommand messed it up?
-    win_close(curwin, true, false);
-    ga_clear(&winsizes);
+  // Create empty command-line buffer.  Be especially cautious of BufLeave
+  // autocommands from do_ecmd(), as cmdwin restrictions do not apply to them!
+  const int newbuf_status = buf_open_scratch(0, _("[Command Line]"));
+  const bool cmdwin_valid = win_valid(cmdwin_win);
+  if (newbuf_status == FAIL || !cmdwin_valid || curwin != cmdwin_win || !win_valid(old_curwin)
+      || !bufref_valid(&old_curbuf) || old_curwin->w_buffer != old_curbuf.br_buf) {
+    if (newbuf_status == OK) {
+      set_bufref(&bufref, curbuf);
+    }
+    if (cmdwin_valid && !last_window(cmdwin_win)) {
+      win_close(cmdwin_win, true, false);
+    }
+    // win_close() autocommands may have already deleted the buffer.
+    if (newbuf_status == OK && bufref_valid(&bufref) && bufref.br_buf != curbuf) {
+      close_buffer(NULL, bufref.br_buf, DOBUF_WIPE, false, false);
+    }
+
     cmdwin_type = 0;
+    cmdwin_level = 0;
     cmdwin_win = NULL;
     cmdwin_old_curwin = NULL;
+    beep_flush();
+    ga_clear(&winsizes);
     return Ctrl_C;
   }
   cmdwin_buf = curbuf;
@@ -4444,11 +4470,12 @@ static int open_cmdwin(void)
 
   exmode_active = save_exmode;
 
-  // Safety check: The old window or buffer was deleted: It's a bug when
-  // this happens!
-  if (!win_valid(old_curwin) || !bufref_valid(&old_curbuf)) {
+  // Safety check: The old window or buffer was changed or deleted: It's a bug
+  // when this happens!
+  if (!win_valid(old_curwin) || !bufref_valid(&old_curbuf)
+      || old_curwin->w_buffer != old_curbuf.br_buf) {
     cmdwin_result = Ctrl_C;
-    emsg(_("E199: Active window or buffer deleted"));
+    emsg(_(e_active_window_or_buffer_changed_or_deleted));
   } else {
     win_T *wp;
     // autocmds may abort script processing

test/old/testdir/test_cmdline.vim

@@ -1885,7 +1885,7 @@ func Test_cmdwin_tabpage()
   tabclose!
 endfunc
 
-func Test_cmdwin_interrupted()
+func Test_cmdwin_interrupted_more_prompt()
   CheckScreendump
 
   " aborting the :smile output caused the cmdline window to use the current

test/old/testdir/test_cmdwin.vim

@@ -121,9 +121,75 @@ func Test_cmdwin_temp_curwin()
 
   call feedkeys("q::call CheckCmdWin()\<CR>:call win_execute(win_getid(winnr('#')), 'call CheckOtherWin()')\<CR>:q<CR>", 'ntx')
 
+  %bwipe!
   delfunc CheckWraps
   delfunc CheckCmdWin
   delfunc CheckOtherWin
 endfunc
 
+func Test_cmdwin_interrupted()
+  func CheckInterrupted()
+    call feedkeys("q::call assert_equal('', getcmdwintype())\<CR>:call assert_equal('', getcmdtype())\<CR>:q<CR>", 'ntx')
+  endfunc
+
+  augroup CmdWin
+
+  " While opening the cmdwin's split:
+  " Close the cmdwin's window.
+  au WinEnter * ++once quit
+  call CheckInterrupted()
+
+  " Close the old window.
+  au WinEnter * ++once execute winnr('#') 'quit'
+  call CheckInterrupted()
+
+  " Switch back to the old window.
+  au WinEnter * ++once wincmd p
+  call CheckInterrupted()
+
+  " Change the old window's buffer.
+  au WinEnter * ++once call win_execute(win_getid(winnr('#')), 'enew')
+  call CheckInterrupted()
+
+  " Using BufLeave autocmds as cmdwin restrictions do not apply to them when
+  " fired from opening the cmdwin...
+  " After opening the cmdwin's split, while creating the cmdwin's buffer:
+  " Delete the cmdwin's buffer.
+  au BufLeave * ++once bwipe
+  call CheckInterrupted()
+
+  " Close the cmdwin's window.
+  au BufLeave * ++once quit
+  call CheckInterrupted()
+
+  " Close the old window.
+  au BufLeave * ++once execute winnr('#') 'quit'
+  call CheckInterrupted()
+
+  " Switch to a different window.
+  au BufLeave * ++once split
+  call CheckInterrupted()
+
+  " Change the old window's buffer.
+  au BufLeave * ++once call win_execute(win_getid(winnr('#')), 'enew')
+  call CheckInterrupted()
+
+  " However, changing the current buffer is OK and does not interrupt.
+  au BufLeave * ++once edit other
+  call feedkeys("q::let t=getcmdwintype()\<CR>:let b=bufnr()\<CR>:clo<CR>", 'ntx')
+  call assert_equal(':', t)
+  call assert_equal(1, bufloaded('other'))
+  call assert_notequal(b, bufnr('other'))
+
+  augroup END
+
+  " No autocmds should remain, but clear the augroup to be sure.
+  augroup CmdWin
+    au!
+  augroup END
+
+  %bwipe!
+  delfunc CheckInterrupted
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab