Add ability to mark block as post content

[fabiankaegy]

When the block editing mode is set to template-lock the template is rendered but all the blocks that are within the template have their block editing mode set to disabled.

All except for the post title, post featured image, and post content blocks.

These are hardcoded into a constant here:

gutenberg/packages/editor/src/components/provider/disable-non-page-content-blocks.js

Lines 8 to 12 in d969294

	const PAGE_CONTENT_BLOCKS = [
	'core/post-title',
	'core/post-featured-image',
	'core/post-content',
	];

There are many ciscumstances where a 3rd party block also reads / writes data to the post object. Whether that is a meta field, a taxonomy or any other custom element.

It would be great it there was a way to identify those blocks to get the same treatment as these three blocks.

Proposed solutions

Maybe a block support would make sense here 🤔

{
    "version": 2,
    "name": "namespace/event-location",
    "title": "Event Location",
    "supports": {
        "postContent": true // very open to other names for this
    }
}

The idea would be that a block can flag that it saves something to the post instead of only saving to local attributes.

[fabiankaegy]

@youknowriad I'd love to get your take on solving this issue with a block support vs a filter / some other approach. Very open to suggestions :)

[Mamaduka]

Makes sense. Developers should be able to mark blocks that qualify as page content for their projects.

cc @noisysocks

[noisysocks]

I'm not sure that a block should care too much about the intricacies of post editing in the site editor. Block are pretty foundational after all. They're often used outside of WordPress, even.

I think I'm more inclined to allow customising this list via a filter.

[fabiankaegy]

Thanks for those insights. @noisysocks as per your suggestion I created a PR that adds a filter to allow overwriting the list: #60068