Re: proposal: edit-rectangle

[Alain Schneble]

John Wiegley <address@hidden> writes:

> This is functionality I'd like to add to rect.el. It allows you to specify a
> rectangular region, and then edit just the contents of that rectangle in a
> separate buffer. When finished (C-c C-c), it replaces the old rectangle using
> insert-rectangle with the new contents.
>
> I'd appreciate comments on usability, fitness, etc.

There's an edge-case when editing rectangular areas spawning beyond end
of lines.  In this situation 'edit-rectangle' followed by
'restore-rectangle' changes the selected area even though no explicit
changes have been committed to that area.  There are phantom whitespace
characters added to some lines.

This is a simple recipe:

(insert
 (with-temp-buffer
   (insert (mapconcat 'identity '("john" "improved" "rectangle" "editing" 
"capabilities" "of" "emacs") "\n"))
   (goto-char 4) ; joh_n
   (rectangle-mark-mode)
   (end-of-line 5) ; capabilities_
   (with-current-buffer (edit-rectangle (mark) (point))
     (restore-rectangle))
   (buffer-string)))

I know it's kind of inherent to fill lines with spaces where needed to
get a rectangular area.  But in this round-trip scenario, it feels not
natural to me.  Not sure if this can be considered a bug though.

(Strangely, in my Emacs it fills some lines with tabs AND spaces.  Not
sure where the tabs come from...)

Alain