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

[Drew Adams <drew.adams@oracle.com>]

[-- Attachment #1: Type: text/plain, Size: 1862 bytes --]

> I think format string asks for more documentation and
> more cognitive effort on part of user :-)  and as such
> maybe it is better to have it as part of Dired+.
> 
> Kind-of more for hard-core users who prefer much
> deeper level of customization?

Emacs users are of all kinds.  No user who
doesn't understand `format' would need to
make that particular option-value choice.

This is no different from options we have
that have a catch-all choice of a function,
which they can use to get pretty much any
behavior.

And that's another reasonable alternative
here to a choice of a format string: a
function that accepts the current switches
as its (first) argument.

That's even more general, and it wouldn't
freak out a user unfamiliar with format
strings. ;-)

And that also covers truncating, trivially.
There's nothing special about truncating.
It just happens to correspond directly to
your immediate problem: a long list of
switches.

Attached is a patch that does what I think
should be done.  The option value can be:

nil - to get the current behavior
`as-is' - show the full switches
an integer - show first N chars of switches
a function - show whatever it returns, when
             passed `dired-actual-switches'

If Emacs doesn't want to go this route then
I guess I'll just use it for Dired+.
___

I do think your suggestion of mouseover
the mode-line indication showing the full
switches is a good one.

I've added command `diredp-change-ls-switches'
to Dired+, and added it to menu-bar menu `Dir'
(aka `Subdir').  It shows the current switches
in the prompt, so you can just hit `C-g' if all
you want is see what the current switches are.

And because it's in the menu, you can get to
it by clicking the lighter in the mode-line.
(Menu `Dir' is the first menu listed when you
click.) 

[-- Attachment #2: dired-2020-05-15a.patch --]
[-- Type: application/octet-stream, Size: 2747 bytes --]

diff -u dired.el dired-2020-05-15a-PATCHED.el
--- dired.el	2020-05-15 11:23:32.804823800 -0700
+++ dired-2020-05-15a-PATCHED.el	2020-05-15 11:26:20.702051000 -0700
@@ -4114,22 +4114,40 @@
   "Non-nil means the Dired sort command is disabled.
 The idea is to set this buffer-locally in special Dired buffers.")
 
+(defcustom dired-switches-in-mode-line nil
+  "How to indicate `dired-actual-switches' in mode-line.
+Possible values:
+ * `nil':    Indicate name-or-date sort order, if possible.
+             Else show full switches.
+ * `as-is':  Show full switches.
+ * Integer:  Show only the first N chars of full switches.
+ * Function: Pass `dired-actual-switches' as arg and show result."
+  :group 'Dired-Plus
+  :type '(choice
+          (const    :tag "Indicate by name or date, else full"   nil)
+          (const    :tag "Show full switches"                    as-is)
+          (integer  :tag "Show first N chars of switches" :value 10)
+          (function :tag "Format with function"           :value identity)))
+
 (defun dired-sort-set-mode-line ()
-  ;; Set mode line display according to dired-actual-switches.
-  ;; Mode line display of "by name" or "by date" guarantees the user a
-  ;; match with the corresponding regexps.  Non-matching switches are
-  ;; shown literally.
+  "Set mode-line according to option `dired-switches-in-mode-line'."
   (when (eq major-mode 'dired-mode)
     (setq mode-name
-	  (let (case-fold-search)
-	    (cond ((string-match-p
-		    dired-sort-by-name-regexp dired-actual-switches)
-		   "Dired by name")
-		  ((string-match-p
-		    dired-sort-by-date-regexp dired-actual-switches)
-		   "Dired by date")
-		  (t
-		   (concat "Dired " dired-actual-switches)))))
+	  (let ((case-fold-search  nil))
+            (if dired-switches-in-mode-line
+                (concat "Dired "
+                        (cond ((integerp dired-switches-in-mode-line)
+                               (substring dired-actual-switches
+                                          0 dired-switches-in-mode-line))
+                              ((functionp dired-switches-in-mode-line)
+                               (format "%s" (funcall dired-switches-in-mode-line
+                                                     dired-actual-switches)))
+                              (t dired-actual-switches)))
+              (cond ((string-match-p dired-sort-by-name-regexp dired-actual-switches)
+                     "Dired by name")
+                    ((string-match-p dired-sort-by-date-regexp dired-actual-switches)
+                     "Dired by date")
+                    (t (concat "Dired " dired-actual-switches))))))
     (force-mode-line-update)))
 
 (define-obsolete-function-alias 'dired-sort-set-modeline