bug#18090: 24.4.50; `delete-selection-helper' logic changed for non-mouse region?

[Juri Linkov <juri@linkov.net>]

>> Shouldn't mouse yanking be supported by `delete-selection-mode',
>> what do you think?
>
> Dunno. Please file a bug report, if you think so. Or
> feel free to bring that into this report, if you like.
>
> What do you want it to do? Does it do what you want if you
> (put 'mouse-yank-primary 'delete-selection 'yank)?
> If not, what code change do you think is needed?

The reason why I asked this question is because it's the only case
what might fail AFAICS.  When I tried what you suggested

(put 'mouse-yank-primary 'delete-selection 'yank)

I see that it pastes at the wrong place - before yanking
it moves point at the offset of the distance between the
region beginning and the position clicked with the mouse,
but since delete-selection-mode already deleted the region,
this means that it puts point at unrelated text that
shifts into this position after deleting the region.

mouse-yank-primary provides the correct result only when
mouse-yank-at-point is non-nil.  I don't see how this could be
supported within the limitations of the current design of
delete-selection-mode.  One way is to reimplement delete-selection-mode
using advices - it's easy to put advice around mouse-yank-at-point
that would set mouse-yank-at-point to t around the call to
mouse-yank-at-point.

Another not so good solution is to hard-code checks for
delete-selection-mode in mouse-yank-primary.

So after mouse-yank-primary is supported, we could look
under what conditions to call (current-kill 1)
in delete-selection-helper.

Please note that the current condition in (eq type 'yank)
that checks for (car kill-ring) is unsuitable
because mouse-yank-primary pastes from
(gui-get-primary-selection), not from (car kill-ring)

>> I agree that code that calls (delete-active-region) under the
>> condition (eq type 'yank) is essential to handle `yank'.
>> But I think that (current-kill 1) is not essential
>> unless it renders yank useless in some cases (yet unknown).
>
> Maybe you're right; dunno.
>
> Do you want to remove that code? Without it, does
> `deletion-selection-mode' do what you want for both
> t and nil values of `mouse-drag-copy-region'?
>
> At this point it's not clear to me what behavior is  bugged,
> if any. I'd like to hear what changes, if any, you propose,
> both for the code and the desired behavior (for both t
> and nil values of `mouse-drag-copy-region').

When mouse-drag-copy-region is non-nil, I see that
(mouse-region-match) returns non-nil, so no changes
are required in delete-selection-helper for this case.