Subject: Re: bug#21275: 24.5; Selection deleted with electric pair mode in cc mode

From: Alan Mackenzie <[email-masked]>
Date: Thu, 20 Aug 2015 21:55:06 +0000

Hello, Drew.

On Thu, Aug 20, 2015 at 02:35:43PM -0700, Drew Adams wrote:
> > > +(defun delete-selection-uses-region-p ()
> > 
> > The way I read it, this name says "a function which tells us if
> > delete-selection uses the region".

> No idea what this is all about, ....

It's for when delete-selection-mode and electric-pair-mode are both
enabled.  What was happening (in C Mode, etc.) was that the user would
mark an object and type "(", expecting e-p-m to put a pair of parens
around the marked object; however d-s-m got in first, and deleted
(?killed) the region before the parens were put around the now empty
region.

There was already a solution for this for when "(" is bound to
self-insert-command - this is fairly arcane, and involves setting a
particular variable to function which returns t in the pertinent
circumstances.

This function was previously coded as a lambda.  However, I needed to
use it for the pertinent CC Mode functions too, so I extracted it into a
defun, giving it the name `delete-selection-uses-region-p'.  The
"delete-seleection" bit is the prefix, shared by the other
de\(fun\|var\)s in the file.

> .... but if this is for `electric-pair-mode' and not for
> `delete-selection-mode' then the name should reflect that - call it
> `electric-pair-SOMETHING'.

It's for when BOTH minor modes are enabled, to enable them to play
nicely with eachother.  But it's in delsel.el, hence the prefix.

> Is this something that `delete-selection-mode' needs?  Or is it
> for something else?

See above.

> > > +  "Return non-nil when the current command uses the region.

> What does it mean for a command to "use the region"?

That isn't very good, is it?  It basically means, from e-p-m's point of
view "I'm going to be "using" the region, so don't you go and delete
it!".

> > It's not about "the current command" but about self-insert-command
> > (which may be the current command or may be called by the current
> > command).

> What does it mean for such a command (or any other command) to
> "use the region"?  That info should presumably be in the doc string.

I think you're right, here.  I'll have another look at it.

-- 
Alan Mackenzie (Nuremberg, Germany).