bug#10624: 24.0.92; default value of `dired-do-ch*'

[Juri Linkov]

> `T c' or `T M-w' copies the tags from the current-line file.
>
> `T p' or `T C-y' pastes those tags to another current-line file,
> adding them to any existing tags for that file.
>
> `T q' pastes similarly, but replaces any existing tags for the target file.
>
> `T > p' (`T > C-y') and `T > q' do the same pasting thing, but for the marked
> files.

Oh no, a whole prefix map for such an auxiliary feature.

But I like the simplicity of your suggestion #2 - use the attributes of the
file on the current line.  It's implemented in a small patch below:

=== modified file 'lisp/dired-aux.el'
--- lisp/dired-aux.el   2012-09-13 23:42:39 +0000
+++ lisp/dired-aux.el   2012-09-16 23:47:32 +0000
@@ -223,10 +247,17 @@ (defun dired-do-chxxx (attribute-name pr
   ;; OP-SYMBOL is the type of operation (for use in `dired-mark-pop-up').
   ;; ARG describes which files to use, as in `dired-get-marked-files'.
   (let* ((files (dired-get-marked-files t arg))
-        (default (and (eq op-symbol 'touch)
-                      (stringp (car files))
-                      (format-time-string "%Y%m%d%H%M.%S"
-                                          (nth 5 (file-attributes (car 
files))))))
+        ;; The source of default file attributes is the file at point.
+        (default-file (dired-get-filename t))
+        (default (when default-file
+                   (cond ((eq op-symbol 'touch)
+                          (format-time-string
+                           "%Y%m%d%H%M.%S"
+                           (nth 5 (file-attributes default-file))))
+                         ((eq op-symbol 'chown)
+                          (nth 2 (file-attributes default-file 'string)))
+                         ((eq op-symbol 'chgrp)
+                          (nth 3 (file-attributes default-file 'string))))))
         (prompt (concat "Change " attribute-name " of %s to"
                         (if (eq op-symbol 'touch)
                             " (default now): "
@@ -263,11 +294,15 @@ (defun dired-do-chxxx (attribute-name pr
 ;;;###autoload
 (defun dired-do-chmod (&optional arg)
   "Change the mode of the marked (or next ARG) files.
-Symbolic modes like `g+w' are allowed."
+Symbolic modes like `g+w' are allowed.
+Type M-n to pull the file attributes of the file at point
+into the minibuffer."
   (interactive "P")
   (let* ((files (dired-get-marked-files t arg))
-        (modestr (and (stringp (car files))
-                      (nth 8 (file-attributes (car files)))))
+        ;; The source of default file attributes is the file at point.
+        (default-file (dired-get-filename t))
+        (modestr (when default-file
+                   (nth 8 (file-attributes default-file))))
         (default
           (and (stringp modestr)
                (string-match "^.\\(...\\)\\(...\\)\\(...\\)$" modestr)
@@ -297,7 +335,9 @@ (defun dired-do-chmod (&optional arg)
 
 ;;;###autoload
 (defun dired-do-chgrp (&optional arg)
-  "Change the group of the marked (or next ARG) files."
+  "Change the group of the marked (or next ARG) files.
+Type M-n to pull the file attributes of the file at point
+into the minibuffer."
   (interactive "P")
   (if (memq system-type '(ms-dos windows-nt))
       (error "chgrp not supported on this system"))
@@ -305,7 +345,9 @@ (defun dired-do-chgrp (&optional arg)
 
 ;;;###autoload
 (defun dired-do-chown (&optional arg)
-  "Change the owner of the marked (or next ARG) files."
+  "Change the owner of the marked (or next ARG) files.
+Type M-n to pull the file attributes of the file at point
+into the minibuffer."
   (interactive "P")
   (if (memq system-type '(ms-dos windows-nt))
       (error "chown not supported on this system"))
@@ -314,7 +356,9 @@ (defun dired-do-chown (&optional arg)
 ;;;###autoload
 (defun dired-do-touch (&optional arg)
   "Change the timestamp of the marked (or next ARG) files.
-This calls touch."
+This calls touch.
+Type M-n to pull the file attributes of the file at point
+into the minibuffer."
   (interactive "P")
   (dired-do-chxxx "Timestamp" dired-touch-program 'touch arg))