Provide the widget preview iframe with a sidebar ID

[dikiyforester]

What problem does this address?

There is no way for a block/widget to identify and get data on the sidebar it’s been placed on.

Prior widget editor, we could get the sidebar id by the widget id, but in block-based widget editor it's impossible since widget id in the editor is not the actual widget id.

For example:

1. Some would like to get the sidebar’s before_title and after_title variables from within the block itself.
2. Some would like to add extra widget fields, depending on the sidebar.

Reported here:

1. https://make.wordpress.org/core/2021/06/29/block-based-widgets-editor-in-wordpress-5-8/#comment-41612
2. https://make.wordpress.org/core/2021/06/29/block-based-widgets-editor-in-wordpress-5-8/#comment-41618

What is your proposed solution?

Add the current sidebar id variable to the block/widget instance in block-based widgets editor.

[kevin940726]

If I'm not misunderstanding this, I think it's a duplicate of #32805?

[cabrerahector]

Not really, @kevin940726. What we want is for the block to be able to access its sidebar data (id, before_widget, after_widget, before_title, after_title, etc).

The issue you're referring to requests for blocks to get assigned a widget_id on the Widgets screen which is sort of similar but not exactly the same thing.

[kevin940726]

@cabrerahector See #32805 (comment), I think we ultimately want the same thing for preview iframes to have the sidebar ids. Am I missing something obvious? 🤔

[noisysocks]

We can’t provide the preview iframe with a widget ID because the ID might not exist in all cases. For example, if a user creates a new Legacy Widget, the ID isn’t created until the user presses Update.

Potentially, we could pass sidebar_id as a widget argument so that plugins can access $args['sidebar_id'] in WP_Widget::widget() to work around this limitation.