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

[Visuwesh]

[ஞாயிறு மே 29, 2022] Eli Zaretskii wrote:

>> From: Visuwesh <visuweshm@gmail.com>
>> Cc: 55692@debbugs.gnu.org
>> Date: Sun, 29 May 2022 11:47:32 +0530
>> 
>> [சனி மே 28, 2022] Eli Zaretskii wrote:
>> 
>> > IMO, we shouldn't distinguish between the mouse and shift-selection
>> > methods of defining the region.  So this feature, if accepted, should
>> > also treat both methods of defining the region the same.
>> 
>> Considering shift-selection would be convenient as well.  Please check
>> attached patch.
>
> Thanks.
>
>> +@vindex delete-selection-temporary-regions-only
>
> I'd drop the "-only" part: it is not necessary, and makes the variable
> name longer.
>

Okay, will do.

>>    By default, text insertion occurs normally even if the mark is
>>  active---for example, typing @kbd{a} inserts the character @samp{a},
>>  then deactivates the mark.  Delete Selection mode, a minor mode,
>>  modifies this behavior: if you enable that mode, then inserting text
>>  while the mark is active causes the text in the region to be deleted
>> -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, then change the variable
>
> There should be cross-references here to where these methods are
> described in the manual.
>

These methods as in "mouse-dragging" or "shift-selection".  I'm afraid I
don't fully understand what you mean.

>> @@ -251,6 +259,10 @@ delete-selection-pre-hook
>>  have this property won't delete the selection.
>>  See `delete-selection-helper'."
>>    (when (and delete-selection-mode (use-region-p)
>> +             (if delete-selection-temporary-regions-only
>> +                 (and (consp transient-mark-mode)
>> +                      (eq (car transient-mark-mode) 'only))
>> +               t)
>
> I wonder whether we should also optionally allow replacing text in
> regions activated by "C-u C-x C-x" when transient-mark-mode is off.
> Those cause transient-mark-mode to have the value 'lambda', not
> '(only...)'.  So maybe the new defcustom should be a tristate, not a
> boolean?
>

Sure, that could be useful.  But I have transient-mark-mode turned on
always so I can't comment much on it.  However, what would the third
state be?  When the defcustom is t, we could have it check for '(only
. ...)' and the value 'lambda', no?

> Also, can we have the above condition in a more elegant form?  In
> general, whenever you have something like
>
>    (if SOMETHING foo t)
>
> it begs to be rewritten so the "t" part is not needed, because 'if'
> itself already returns a boolean value.

Sure.  I will factor out the condition into a separate function.  Is
that more elegant?

I will send an updated patch a bit later.  Thanks.