Introduces PluginSettingsSidebar slotfill to the Document sidebar.

[ryanwelcher]

Description

Introduce a new slotFill below Status & Availability panel in the Document sidebar.
Closes #13357

How has this been tested?

This has been testing locally and there are tests on the PR.

Screenshots

Types of changes

New feature that only affects the settings-sidebar component.

Checklist:

• My code is tested.
• My code follows the WordPress code style.
• My code follows the accessibility standards.
• My code has proper inline documentation.
• I've included developer documentation if appropriate.

Basic Usage Example:

const { registerPlugin } = wp.plugins;
const { PluginDocumentSetting } = wp.editPost;

const MyDocumentSettingTest = () => (
	<PluginDocumentSetting className="my-document-setting-plugin">
		<p>My Document Setting Panel</p>
	</PluginDocumentSetting>
);

registerPlugin( 'document-setting-test', { render: MyDocumentSettingTest } );

[adamsilverstein]

LGTM! This is an elegant solution to a useful extension point.

[youknowriad]

Referring to the related slack discussion. https://wordpress.slack.com/archives/C02QB2JS7/p1545318632348900

Let's wait a bit before introducing this as Phase 2 work could have an impact on backward compatibilty here.

[gziolo]

Noting, that there is also a tutorial which explains how to create a sidebar for your plugin - - it would be an alternative supported as of today:
https://github.com/WordPress/gutenberg/blob/master/docs/designers-developers/developers/tutorials/sidebar-tutorial/plugin-sidebar-0.md

There was also a related discussion on Twitter on that topic during the weekend:

https://twitter.com/AlexStandiford/status/1086313778625593344

There was mention of the article by @ocean90:
https://dominikschilling.de/how-to-edit-post-meta-outside-of-a-gutenberg-block/

[gziolo]

@youknowriad any new thoughts on this proposal? Code wise it looks solid. There is only the question related to the UI considerations and how does it fit in the wider picture of the block editor on other screens like the widget one.

[youknowriad]

I think we can explore this a bit further now. The original reasons for delaying this are still valid (could become an inspector control in phase 2 if we ever introduce a "Document" or "Post" block) but it feels a bit too seen and this use-case is legit.

Can we expaned the description of the PR with a plugin example to test it?

I think we should rename this to DocumentSetting as it's a more semantic name that sets the expectation that this is about adding new document settings. They are now displayed in the document panel but the framework (editor) can display them in a different way if needed.

Also, is there a way to display the plugin icon in the panel header (to clarify the origin of the panel).

[youknowriad]

We might also want to include those custom panels in the Options dialog so users could disable them the same way they can do it for all other panels.

Yeah, this seems like something that is needed. I'm fine if it's a separate PR though. Whatever works best for you all.

[youknowriad]

Tested this, it works great. A few questions:

• Will we need an id to "enable/disable" the panel or is the plugin's identifier sufficient?
• It does feel like we may need a way to define the position (or at least a priority or something like that) for the panel. (Also something that we can explore separately).

[ryanwelcher]

@youknowriad I was able to remove the custom panels using removePanel and looking up the id in the markup.

I have been thinking about the priority aspect as well, I was thinking that adding it to registerPlugin() may make sense. This will give us the flexibility to add it to other SlotFills in the future and also for the existing ones such as PluginPrePublishPanel and PluginPostPublishPanel - both of which could benefit from it.

[ryanwelcher]

@gziolo @youknowriad I've updated the e2e test and everything is passing. Is there anything else that needs to be addressed on this?

[ryanwelcher]

@youknowriad I have created #16384 as an approach to manage priority. Any feedback is apprectiated!

[youknowriad]

@aduth any thougs on the naming?

[aduth]

Seems fine to me as proposed.