[wp-trac] [WordPress Trac] #35574: Add schema information to WP_Widget (was: Add default instance information to WP_Widget)

[WordPress Trac]

#35574: Add schema information to WP_Widget
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 Reporter:  westonruter                   |       Owner:
     Type:  enhancement                   |      Status:  new
 Priority:  normal                        |   Milestone:  Future Release
Component:  Widgets                       |     Version:  2.8
 Severity:  normal                        |  Resolution:
 Keywords:  needs-patch needs-unit-tests  |     Focuses:
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Description changed by westonruter:

Old description:

> Widgets often have duplicated logic between the `WP_Widget::widget()`,
> `WP_Widget::update()`, and `WP_Widget::form()` methods for checking if a
> given `$instance` property has been set, and if not, supplying a default
> value. In some cases, these `isset` checks are ''not'' performed
> resulting in PHP notices if the methods are programmatically invoked with
> an empty array. I suggest that we introduce a
> `WP_Widget::$default_instance` property or
> `WP_Widget::get_default_instance()` method that will return the
> `$instance` defaults that can be merged on top of with the current
> `$instance`.

New description:

 Widgets often have duplicated logic between the `WP_Widget::widget()`,
 `WP_Widget::update()`, and `WP_Widget::form()` methods for checking if a
 given `$instance` property has been set, and if not, supplying a default
 value. In some cases, these `isset` checks are ''not'' performed resulting
 in PHP notices if the methods are programmatically invoked with an empty
 array. I suggest that we introduce a `WP_Widget::$default_instance`
 property or `WP_Widget::get_default_instance()` method that will return
 the `$instance` defaults that can be merged on top of with the current
 `$instance`.

 With the REST API, there is an emerging-established way in WordPress for
 describing a data structure, such as a widget instance. One aspect of the
 REST API endpoint schema is the `default` values for given fields on a
 property.

 Widgets in WordPress are assumed to be arrays, with the applied filters
 and function return values. With a schema defined, the data type of a
 widget instance would be guaranteed. Meta in the REST API is a challenge
 given that it may or may not contain serialized PHP. Widgets are stored in
 serialized PHP arrays in WP options (though it is possible to store them
 in posts, per #32474). Additionally, the instance arrays may also contain
 PHP objects for classes that cannot be cleanly serialized into JSON, and
 having a REST API JSON schema defined for a widget would guarantee that a
 widget instance can be represented in JSON. This would, in turn, allow
 widgets to be exposed as [https://github.com/WP-API/WP-API/issues/19
 endpoints] in the REST API, and it would allow widget instances to be
 completely manipulated with JavaScript (such as in the Customizer, as
 described in #33507).

 By adding schema information to `WP_Widget`, we get a lot more than having
 default `$instance` data available. For one, the widget form can be
 automatically generated based on the schema if one is not defined (i.e. if
 `noform` is returned from the `WP_Widget::form()` method). (This may
 actually be focus of the Fields API.)

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Ticket URL: <https://core.trac.wordpress.org/ticket/35574#comment:6>
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