bug#81522: 32.0.50; dired-auto-toggle-b-switch problem with subdirectory and custom switches

This is a follow up to bug#81295, the relevant discussion is starting
from this message:
https://debbugs.gnu.org/cgi/bugreport.cgi?bug=81295#20.

In particular, here's some analysis and a possible way of fixing it:
https://debbugs.gnu.org/cgi/bugreport.cgi?bug=81295#29.


- mkdir -p ~/tmp/1/2

- emacs -Q -nw --eval "(setopt dired-auto-toggle-b-switch t)"

- C-x d ~/tmp/1 RET

- Create file with newline in name in subdir: M-! touch "2/a\nb.txt"
  (C-q C-j for '\n')

- Type C-u i RET on directory '2' to open it in the same buffer.  In
  bug#81295 the case of just "i" was fixed, this bug is about the case
  with custom switches.

- Observe that the subdir is not inserted at all, and a warning is
  displayed.  This happens only when 2 contains file with newlines.

Thanks.


In GNU Emacs 32.0.50 (build 17, aarch64-apple-darwin25.5.0, NS
 appkit-2685.60 Version 26.5.2 (Build 25F84)) of 2026-07-30 built on
 mac2598
Repository revision: fb6ad8aa780df52b01dc018a283b11db33ded906
Repository branch: master
System Description: macOS 26.5.2