bug#20626: Wishlist: M-x shell-command-on-rectangle-region

[Juri Linkov <juri@linkov.net>]

>> Wishlist:
>> M-x shell-command-on-rectangle-region
>
> As you can see in bug#20070, the effort to make commands rectangleable
> had stalled some time ago due to the need to decide how to handle
> backward-compatibility of the existing region arguments, e.g. in
>
>   (shell-command-on-region START END COMMAND &optional OUTPUT-BUFFER REPLACE
>                            ERROR-BUFFER DISPLAY-ERROR-BUFFER)
>
> how to send the boundaries of the rectangular region in START and END.
>
> One idea is to handle it like recently we handled backward-compatibility
> for saving dired positions in saveplace.el where we used a new format like
>
>   ("~" (dired-filename . "~/.emacs.d/places"))
>
> Using something like this means sending the rectangular bounds
> either in START or END in the new format like
>
>   (rect (1 . 2) (3 . 4))

Sorry, I was wrong.  I realized now that query-replace has quite
a different requirement.  query-replace needs rectangular boundaries
to limit the search for replacements, whereas shell-command-on-region
should extract the rectangular region as strings and replace it with
the result of the command.  Here is a working prototype that demonstrates
its possible implementation:

(define-advice shell-command-on-region
    (:around (orig-fun start end command
                       &optional output-buffer replace
                       error-buffer display-error-buffer))
  (if (and (boundp 'rectangle-mark-mode) rectangle-mark-mode)
      (let ((input (mapconcat 'identity (delete-extract-rectangle start end) "\n"))
            output)
        (with-temp-buffer
          (insert input)
          (call-process-region (point-min) (point-max)
                               shell-file-name t t
                               nil shell-command-switch
                               command)
          (setq output (split-string (buffer-string) "\n")))
        (goto-char start)
        (insert-rectangle output))
    (funcall orig-fun start end command
             output-buffer replace
             error-buffer display-error-buffer)))

This is another case to take into account when designing the interface,
i.e. in this case the list of boundaries in the arg START is not necessary,
and I have no idea how to avoid `(if (and (boundp 'rectangle-mark-mode)
rectangle-mark-mode))'