bug#62732: 29.0.60; uniquify-trailing-separator-p affects any buffer whose name matches a dir in CWD

[Stefan Monnier via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>]

>>> This inspired me to do something not exactly this but which also gets
>>> rid of the new argument to create-file-buffer.  How about this:
>>
>> Now you're talking!  :-)
>> LGTM!  Thank you very much,
>
> Great!  Here's that as a complete patch again.

Eli, OK to install on `master`?


        Stefan


PS: Nitpicks:

> +  (let* ((lastname (if (directory-name-p filename)
> +                       (file-name-nondirectory (directory-file-name filename))
> +                     (file-name-nondirectory filename)))

Aka

     (let* ((lastname (file-name-nondirectory
                       (if (directory-name-p filename)
                           (directory-file-name filename)
                         filename)))

or even just

     (let* ((lastname (file-name-nondirectory
                       (directory-file-name filename)))

> +         (lastname (if (and (directory-name-p filename) uniquify-trailing-separator-p)
> +                       (cond ((eq uniquify-buffer-name-style 'forward)
> +	                      (file-name-as-directory lastname))
> +	                     ((eq uniquify-buffer-name-style 'reverse)
> +	                      (concat (or uniquify-separator "\\") lastname))
> +                             (t lastname))
> +                     lastname))

Here you can merge the `if` into the `cond` and I'd test
`uniquify-trailing-separator-p` first (cheaper and nil by default)
and since we know (directory-name-p filename), I'd be tempted to replace
(file-name-as-directory lastname) with just `filename`.  Also I'd argue
that when `uniquify-trailing-separator-p` and (directory-name-p
filename) are both true we never want to use just `lastname` so the
default should be to return `filename`:

            (lastname (cond
                       ((not (and uniquify-trailing-separator-p (directory-name-p filename)))
                        lastname)
                       ((eq uniquify-buffer-name-style 'reverse)
                        (concat (or uniquify-separator "\\") lastname))
                       (t filename)))

so for `post-forward` (my personal favorite) /foo/bar/mumble/name/ would
turn into name/|bar/mumble.
WDYT?


        Stefan