bug#66155: 'electric-pair-inhibit-if-helps-balance' has side-effects

[Stefan Kangas <stefankangas@gmail.com>]

Akib Azmain Turja <akib@disroot.org> writes:

> With the default configuration (which uses
> 'electric-pair-inhibit-if-helps-balance'), inserting parens at the end
> of a Tempel field doesn't extend the field.
>
> I think the modify+undo magic in electric-pair-inhibit-if-helps-balance
> moves markers.
>
> The following is the solution that works for me atleast; it uses insert
> to insert back the character, and let-bind buffer-undo-list to not
> clobber the undo list.
>
> (defun *electric-pair-inhibit-if-helps-balance (char)
>   "Return non-nil if auto-pairing of CHAR would hurt parens' balance.
>
> Works by first removing the character from the buffer, then doing
> some list calculations, finally restoring the situation as if nothing
> happened."
>   (pcase (electric-pair-syntax-info char)
>     (`(,syntax ,pair ,_ ,s-or-c)
>      (let ((buffer-undo-list t))
>        ;; Don't use `delete-char'; that may modify the head of the
>        ;; undo list.
>        (delete-region (point) (1- (point)))
>        (let ((ret
>               (cond
>                ((eq ?\( syntax)
>                 (let* ((pair-data
>                         (electric-pair--balance-info 1 s-or-c))
>                        (outermost (cdr pair-data)))
>                   (cond ((car outermost)
>                          nil)
>                         (t
>                          (eq (cdr outermost) pair)))))
>                ((eq syntax ?\")
>                 (electric-pair--unbalanced-strings-p char)))))
>          (insert (string char))
>          ret)))))

Could you please send the patch as an attachment instead?  We prefer
that patches are created with a command like `git format-patch -1'.

Please also include:

- The bug number of this bug in the commit message, like so: Bug#66155

- A ChangeLog entry, as described in the file CONTRIBUTE.

That would make it easier for us to review and hopefully install
this patch.  Thanks in advance.