bug#71337: 30.0.50; `electric-pair-mode' and custom keybinding

[Eli Zaretskii <eliz@gnu.org>]

On June 4, 2024 1:09:09 PM GMT+03:00, Stephen Berman <stephen.berman@gmx.net> wrote:
> On Tue, 04 Jun 2024 12:24:59 +0300 Eli Zaretskii <eliz@gnu.org> wrote:
> 
> > On June 4, 2024 11:08:51 AM GMT+03:00, "João Távora" <joaotavora@gmail.com> wrote:
> >> On Tue, Jun 4, 2024 at 8:37 AM João Távora <joaotavora@gmail.com> wrote:
> >> 
> >> I've had a look.  it looks like the problems is e-p-mode's assumption
> >> that last-command-event is the thing to be inserted.  The fact that
> >> it isn't here (somehow an innocent 92 is now a monstrous 8388643),
> >> triggers the problem (8388643 isn't a representation of a character,
> >> apparently).
> >> 
> >> But according to the docstring of post-self-insert-hook,
> >> the assumption seems sane, and I probably coded for it.
> >> 
> >>   post-self-insert-hook is a variable defined in `src/cmds.c'.
> >> 
> >>   ...
> >> 
> >>   The hook can access the inserted character via `last-command-event'.
> >>   ...
> >> 
> >> I don't think the patch is fully correct.  I think Stefan is the right
> >> person to call here.  I've had an even briefer look at cmds.c and I
> >> don't understand how that hook's promise is honoured.
> >
> >
> > It looks like Arash made the mistake of being the first one, ever, of invoking
> > self-insert-command from Lisp with 2nd arg non-nil, and turning on
> > electric-pair-mode on top of that.  When self-insert-command is called with 2
> > args, it uses the 2nd arg as the character to insert, but it does NOT
> > overwrite last-command-event with that character.  So post-self-insert-hook
> > sees the wrong event and rightfully barfs.
> >
> > Which means the patch proposed by Stephen is not TRT, because it means
> > electric-pair-mode will ignore the inserted backslashes.
> 
> My patch should only make electric-pair-mode ignore key sequences which
> don't satisfy characterp, e.g. "s-#" or "C-#".  I just tested my patch
> after giving ?\ open parenthesis syntax, binding it to "C-#" and
> enabling electric-pair-mode, and what I see is that typing `C-#' inserts
> a "\" while typing `\' insert "\\".  Is this not the desired behavior?
> (Of course, that doesn't means a lower-level change isn't preferable.)
> 
> Steve Berman
> 
> 

My point is that if a character is inserted by Arash's command, your patch might ignore it, depending on the command's binding.