bug#55692: 29.0.50; delete-selection-mode: Replace region only if set using the mouse

[Eli Zaretskii]

> From: Visuwesh <visuweshm@gmail.com>
> Cc: 55692@debbugs.gnu.org
> Date: Sun, 29 May 2022 20:23:49 +0530
> 
> >> Sure.  I will factor out the condition into a separate function.  Is
> >> that more elegant?
> >
> > No, that's overkill.  I meant that if you need an 'if' to return t or
> > something else, you could instead make it return nil or something
> > else, as in
> >
> >    (if SOMETHING foo)
> >
> > and reverse the condition.
> >
> > But if you still don't understand, just forget this comment.
> 
> I don't think I fully understood what you meant but I took a shot at it
> anyway.  Please review updated patch.

Well, that uses double negation, which IME is a sign that it can be
clarified.  Is the following condition correct?

  (when (and delete-selection-mode
             (use-region-p)
             (not buffer-read-only)
             (or (null delete-selection-temporary-region)
                 (and (eq delete-selection-temporary-region 'selection)
                      (consp transient-mark-mode)
                      (eq (car transient-mark-mode) 'only))
                 (and delete-selection-temporary-region
                      (or (eq transient-mark-mode 'lambda)
                          (and (consp transient-mark-mode)
                               (eq (car transient-mark-mode) 'only))))))

If not, why not?

> -first.  To toggle Delete Selection mode on or off, type @kbd{M-x
> -delete-selection-mode}.
> +first.  If you want to replace only temporary regions, set by
> +mouse-dragging or shift-selection (@pxref{Setting Mark}) or @kbd{C-u
> +C-x C-x}, then change the variable
> +@code{delete-selection-temporary-region} to @code{t}.  But if you do
> +not want to consider the region made active by @kbd{C-u C-x C-x}
> +(@pxref{Disabled Transient Mark}), then set the variable to
> +@code{selection}.  To toggle Delete Selection mode on or off, type
> +@kbd{M-x delete-selection-mode}.

This text is now too complex and thus confusing.  (You can only keep
using that style for boolean options.)  I would rephrase:

  Normally, inserting text deletes any active region, replacing it
  with the text you insert.  However, you can tune this behavior by
  customizing the @code{delete-selection-temporary-region} option.
  Its default value is @code{nil}, but you can set it to @code{t}, in
  which case only temporarily-active regions will be replaced: those
  which are set by dragging the mouse (@pxref{Setting Mark}) or by
  shift-selection (@pxref{Shift Selection}), as well as by @kbd{C-u
  C-x C-x} when Transient Mark mode is disabled.  You can further tune
  the behavior by setting @code{delete-selection-temporary-region} to
  @code{selection}: then temporary regions activated by @kbd{C-u C-x
  C-x} won't be replaced, only the ones activated by dragging the
  mouse or shift-selection.

OK?