bug#41250: 28.0.50; Dired displays unconditionally ls-switches on modeline

[Juri Linkov]

> There is no way to turn off displaying of ls-switches on modeline when
> in dired-mode.
>
> By default in certain configuration, dired display ls-switches on
> modeline. In case those switches are a long list, for example:
>
> "-lA --si --time-style long-iso --group-directories-first"
>
> then everything else on modeline gets pushed far to the right which is
> not very usable. In general I don't have much use of seing ls-switches
> on modeline and would like to be able to turn them off. As of current it
> does not seem possible since it is hard-coded in function
> `dired-sort-set-mode-line' in dired.el.
>
> I suggest, as small improvement, to introduce a user option to turn off
> or on displaying of ls-switches on modeline. As a suggestion I have
> attached small hack to dired.el as tested on my copy of Emacs, but you
> might wish to rewrite it. Drew had some other suggestions.

Maybe instead of boolean better to use a number for the allowed limit
that should not grow more than this number that means the length of
switches string that the user can tolerate on the modeline.

Then modeline will display abbreviation truncated to the specified
number of characters, with an ellipses, on the assumption that
the most important switches are at the beginning of the string.
Customizing it to 0 effectively disables the display of switches.