bug#23298: 25.0.92; electric-pair-delete-pair doesn't check if parens are balanced

bug#23298: 25.0.92; electric-pair-delete-pair doesn't check if parens are balanced

[Mohammed Sadik]

When pressing Backspace key, with electric-pair-mode enabled,
it unconditionally deletes the following char, if its the matching pair.
Ideally, it may better check if it breaks the equilibrium of
braces/quotes.

Eg: code: (char-before (point))
                             |_ point location
If my point (cursor) is just before the last paren (the cursor is
blinking on the last paren), and I press backspace until the beginning
of "point"[0], and then one char back[1], it just deletes the bracket,
without checking if the parens are balanced.

code:
        [0] (char-before ()
                         |_point location
        [1] (char-before
                        |_ point location

This could be the case of quotes, braces, etc.

In GNU Emacs 25.0.92.1 (x86_64-unknown-linux-gnu, GTK+ Version 3.18.9)
 of 2016-04-13 built on fedora.localdomain
Windowing system distributor 'Fedora Project', version 11.0.11800000
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bug#23298: 25.0.92; electric-pair-delete-pair doesn't check if parens are balanced

[Lars Ingebrigtsen]

Mohammed Sadik <sadiq@sadiqpk.org> writes:

> When pressing Backspace key, with electric-pair-mode enabled,
> it unconditionally deletes the following char, if its the matching pair.
> Ideally, it may better check if it breaks the equilibrium of
> braces/quotes.
>
> Eg: code: (char-before (point))
>                              |_ point location
> If my point (cursor) is just before the last paren (the cursor is
> blinking on the last paren), and I press backspace until the beginning
> of "point"[0], and then one char back[1], it just deletes the bracket,
> without checking if the parens are balanced.
>
> code:
>         [0] (char-before ()
>                          |_point location
>         [1] (char-before
>                         |_ point location
>
> This could be the case of quotes, braces, etc.

(I'm going through old Emacs bug reports that haven't received any
response.)

Or a simpler example:

(foo ()

If you put point after the next-to-last character, then hitting DEL will
delete the last pair:

(foo 

But...  I don't think this is a bug?  electric-pair-mode doesn't promise
to keep things balanced globally, but delete the matching pair if you
delete an opening parenthesis?  I think.

Does that tally with what everybody else would expect?

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no

bug#23298: 25.0.92; electric-pair-delete-pair doesn't check if parens are balanced

[Stefan Kangas]

Lars Ingebrigtsen <larsi@gnus.org> writes:

> Mohammed Sadik <sadiq@sadiqpk.org> writes:
>
>> When pressing Backspace key, with electric-pair-mode enabled,
>> it unconditionally deletes the following char, if its the matching pair.
>> Ideally, it may better check if it breaks the equilibrium of
>> braces/quotes.
>>
>> Eg: code: (char-before (point))
>>                              |_ point location
>> If my point (cursor) is just before the last paren (the cursor is
>> blinking on the last paren), and I press backspace until the beginning
>> of "point"[0], and then one char back[1], it just deletes the bracket,
>> without checking if the parens are balanced.
>>
>> code:
>>         [0] (char-before ()
>>                          |_point location
>>         [1] (char-before
>>                         |_ point location
>>
>> This could be the case of quotes, braces, etc.
>
> (I'm going through old Emacs bug reports that haven't received any
> response.)
>
> Or a simpler example:
>
> (foo ()
>
> If you put point after the next-to-last character, then hitting DEL will
> delete the last pair:
>
> (foo
>
> But...  I don't think this is a bug?  electric-pair-mode doesn't promise
> to keep things balanced globally, but delete the matching pair if you
> delete an opening parenthesis?  I think.
>
> Does that tally with what everybody else would expect?

Do we have any electric-pair-mode users who could comment on this?

Best regards,
Stefan Kangas

bug#23298: 25.0.92; electric-pair-delete-pair doesn't check if parens are balanced

[Andrii Kolomoiets]

Stefan Kangas <stefan@marxist.se> writes:

>> Or a simpler example:
>>
>> (foo ()
>>
>> If you put point after the next-to-last character, then hitting DEL will
>> delete the last pair:
>>
>> (foo
>>
>> But...  I don't think this is a bug?  electric-pair-mode doesn't promise
>> to keep things balanced globally, but delete the matching pair if you
>> delete an opening parenthesis?  I think.
>>
>> Does that tally with what everybody else would expect?
>
> Do we have any electric-pair-mode users who could comment on this?

I for one wish electric-pair-mode to leave balanced closing parenthesis
in this case.