bug#41946: 27.0.91; native json parsing: add :empty-object configuration

bug#41946: 27.0.91; native json parsing: add :empty-object configuration

[Ivan Yonchovski]

This is similar to :null-object/:false-object flags in
json-parse-string and solves the same issue - inability to distinguish
json's null from {}.

bug#41946: 27.0.91; native json parsing: add :empty-object configuration

[Eli Zaretskii]

> From: Ivan Yonchovski <yyoncho@gmail.com>
> Date: Fri, 19 Jun 2020 08:52:57 +0300
> 
> 
> This is similar to :null-object/:false-object flags in
> json-parse-string and solves the same issue - inability to distinguish
> json's null from {}.

I don't think I understand the request.  Can you post more details,
please?  (Maybe it's some standard JSON feature that I'm not familiar
with?)

bug#41946: 27.0.91; native json parsing: add :empty-object configuration

[yyoncho]

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Sorry, for the short description. Here it is what I can do now:

(json-parse-string  "{\"a\":null}"
                    :object-type 'plist
                    :null-object :null-object)
=> (:a :null-object)

Here it is what I want to be able to do also:

(json-parse-string  "{\"a\":{}}"
                    :object-type 'plist
                    :empty-object :empty)
=> (:a :empty)

The purpose of this flag is to be able to distinguish json's null from
json's empty object.
ATM this could be achieved only by binding null. I want to be able to bind
an empty object as well.

Thanks,
Ivan

On Fri, Jun 19, 2020 at 10:30 AM Eli Zaretskii <eliz@gnu.org> wrote:

> > From: Ivan Yonchovski <yyoncho@gmail.com>
> > Date: Fri, 19 Jun 2020 08:52:57 +0300
> >
> >
> > This is similar to :null-object/:false-object flags in
> > json-parse-string and solves the same issue - inability to distinguish
> > json's null from {}.
>
> I don't think I understand the request.  Can you post more details,
> please?  (Maybe it's some standard JSON feature that I'm not familiar
> with?)
>

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bug#41946: 27.0.91; native json parsing: add :empty-object configuration

[Lars Ingebrigtsen]

yyoncho <yyoncho@gmail.com> writes:

> Sorry, for the short description. Here it is what I can do now:
>
> (json-parse-string  "{\"a\":null}"
>                     :object-type 'plist
>                     :null-object :null-object)
> => (:a :null-object)
>
> Here it is what I want to be able to do also:
>
> (json-parse-string  "{\"a\":{}}"
>                     :object-type 'plist
>                     :empty-object :empty) 
> => (:a :empty)
>
> The purpose of this flag is to be able to distinguish json's null from json's empty
> object.
> ATM this could be achieved only by binding null. I want to be able to bind an
> empty object as well.

I'm not sure I understand the request.  

(json-parse-string  "{\"a\":null, \"b\":{}}"
                    :object-type 'plist)
=> (:a :null :b nil)

(json-parse-string  "{\"a\":null, \"b\":{}}"
                    :object-type 'plist
                    :null-object :null-object)
=> (:a :null-object :b nil)                    

By binding :null-object, you can distinguish these objects already, so
:empty-object would just be the opposite?  And you can do that in
post-filtering if you want something like that.

But I've added Philipp to the CCs; perhaps he has a comment here.

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

bug#41946: 27.0.91; native json parsing: add :empty-object configuration

[yyoncho]

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We already have 20k+ LOC project using json null as nil and rebinding it
will force us to rewrite a great portion of the if statements.

Thanks,
Ivan

On Sat, Jul 31, 2021 at 6:07 PM Lars Ingebrigtsen <larsi@gnus.org> wrote:

> yyoncho <yyoncho@gmail.com> writes:
>
> > Sorry, for the short description. Here it is what I can do now:
> >
> > (json-parse-string  "{\"a\":null}"
> >                     :object-type 'plist
> >                     :null-object :null-object)
> > => (:a :null-object)
> >
> > Here it is what I want to be able to do also:
> >
> > (json-parse-string  "{\"a\":{}}"
> >                     :object-type 'plist
> >                     :empty-object :empty)
> > => (:a :empty)
> >
> > The purpose of this flag is to be able to distinguish json's null from
> json's empty
> > object.
> > ATM this could be achieved only by binding null. I want to be able to
> bind an
> > empty object as well.
>
> I'm not sure I understand the request.
>
> (json-parse-string  "{\"a\":null, \"b\":{}}"
>                     :object-type 'plist)
> => (:a :null :b nil)
>
> (json-parse-string  "{\"a\":null, \"b\":{}}"
>                     :object-type 'plist
>                     :null-object :null-object)
> => (:a :null-object :b nil)
>
> By binding :null-object, you can distinguish these objects already, so
> :empty-object would just be the opposite?  And you can do that in
> post-filtering if you want something like that.
>
> But I've added Philipp to the CCs; perhaps he has a comment here.
>
> --
> (domestic pets only, the antidote for overdose, milk.)
>    bloggy blog: http://lars.ingebrigtsen.no
>

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bug#41946: 27.0.91; native json parsing: add :empty-object configuration

[Lars Ingebrigtsen]

yyoncho <yyoncho@gmail.com> writes:

> We already have 20k+ LOC project using json null as nil and rebinding it will
> force us to rewrite a great portion of the if statements.

You can wrap the json calls with a function that flips nil/:empty-object
easy enough, can't you?

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

bug#41946: 27.0.91; native json parsing: add :empty-object configuration

[Dmitry Gutov]

On 31.07.2021 19:12, Lars Ingebrigtsen wrote:
> You can wrap the json calls with a function that flips nil/:empty-object
> easy enough, can't you?

By copying the object tree and substituting nil for something else 
recursively?

That says "more GC" to me, which can be a problem when the structure is 
big enough.

bug#41946: 27.0.91; native json parsing: add :empty-object configuration

[Lars Ingebrigtsen]

Dmitry Gutov <dgutov@yandex.ru> writes:

> On 31.07.2021 19:12, Lars Ingebrigtsen wrote:
>> You can wrap the json calls with a function that flips nil/:empty-object
>> easy enough, can't you?
>
> By copying the object tree and substituting nil for something else
> recursively?
>
> That says "more GC" to me, which can be a problem when the structure
> is big enough.

The user didn't want to rewrite the code to alter some conditionals, and
instead wanted Emacs to be changed so that they didn't have to do that.
I pointed out that the user can trivially just pre-process the data if
they didn't want to rewrite those conditionals.

(And they can just modify the structure in place if GC's a concern.)

I think the conclusion here is that we don't want to add :empty-object
to json.c, so I'm closing this bug report.

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

bug#41946: 27.0.91; native json parsing: add :empty-object configuration

[Dmitry Gutov]

On 04.08.2021 08:55, Lars Ingebrigtsen wrote:
> The user didn't want to rewrite the code to alter some conditionals, and
> instead wanted Emacs to be changed so that they didn't have to do that.
> I pointed out that the user can trivially just pre-process the data if
> they didn't want to rewrite those conditionals.

It's not like the request is illogical (empty object can also be 
conflated with empty array if json-array-type is 'list'), or it would 
take much effort to implement.

I don't have the time to work on this now, though, so I concede to 
whatever is decided here.