bug#46397: 27.1; Cannot delete buffer pointing to a file in a path that includes a file

[Matt Armstrong]

"Peter" <craven@gmx.net> writes:

> The following steps reproduce this:
> - Make sure /tmp/tmp does not exist
> - Open a buffer /tmp/tmp/foo.txt
> - Make some changes to the buffer.
> - Do *not* save the buffer or create the directory /tmp/tmp/
> - Create /tmp/tmp as a *file* (not a directory)
> - Try to kill the buffer.
>
> You will see the following error message:
>
> Unlocking file: Not a directory, /tmp/tmp/foo.txt
>
> I just want to kill the buffer, I don't want to save it.
>
> This is easily rectified by just deleting / moving away /tmp/tmp, but it
> seems like this could be resolved to just delete the buffer.

I confirmed this in 27.1 and the master branch. I also found it
difficult to exit Emacs once this state was reached. If you choose "no"
when saving modified buffers Emacs hits this error and is left in a
strange state (there are no displayed buffers or mode line, but Emacs is
still running).

The backtrace is unsurprising:

Debugger entered--Lisp error: (file-error "Unlocking file" "Not a directory" 
"/private/tmp/tmp/test.txt")
  kill-buffer("test.txt")
  funcall-interactively(kill-buffer "test.txt")
  call-interactively(kill-buffer nil nil)
  command-execute(kill-buffer)