Subscriptions: add block binding returning subscriber count

[simison]

Adds new block binding API for subscriptions, available in WP 6.5. (Dev note)

With block:

<!-- wp:paragraph {"metadata":{"bindings":{"content":{"source":"jetpack/subscribers","args":{"key":"count"}}}}} -->
<p>Subscribers</p>
<!-- /wp:paragraph -->

You would get in the frontend of the post:

Same text should appear in the editor, but at least for me I just see binding paragraph but no text:

Proposed changes:

• Adds new block binding API for subscriptions, available in WP 6.5

Other information:

• Have you written new tests for your changes, if applicable?
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Jetpack product discussion

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Testing instructions:

• You need to run WP 6.5 RC for this to work.

[github-actions]

Are you an Automattician? Please test your changes on all WordPress.com environments to help mitigate accidental explosions.

• To test on WoA, go to the Plugins menu on a WordPress.com Simple site. Click on the "Upload" button and follow the upgrade flow to be able to upload, install, and activate the Jetpack Beta plugin. Once the plugin is active, go to Jetpack > Jetpack Beta, select your plugin, and enable the try/block-bindings-api-for-subscriptions branch.

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[nerrad]

Same text should appear in the editor, but at least for me I just see binding paragraph but no text:

I think that's expected, the fallback content is what gets displayed in the editor because depending on the source, the rendered value can only be derived from the context. There are exceptions, like your example, since count of subscribers is a global thing but I imagine that's something that could be iterated on upstream.

[simison]

Yeah, I figured the text doesn't show in editor either because of some combo of WP trunk/ Gutenberg trunk I had, or indeed because I'm not actually pulling a post meta but more of a global thing.

This kind of binding would be indeed more useful in site editor templates or pages, rather than in blog posts, anyway.

[retrofox]

If I'm not wrong, you need to register the handler in the client, as core does when registering the core/post-meta handler here.

The action hasn't been exposed and it's usable internally for now 😬

[retrofox]

This kind of binding would be indeed more useful in site editor templates or pages, rather than in blog posts, anyway.

I kind of disagree :-D. I imagine many cases where API can be used in the context of the post editor.
For instance, all blocks that pull the data from the post entity (core/post-title, core/post-excerpt, etc) could be replaced by classic blocks (core/paragraph, core/heading) simply by binding the attribute with the proper entity property (tongue twister for free)

[simison]

@retrofox I totally agree with you on those points but I meant for subscriber count specifically, which is the kind of info publishers would be presented outside the post content most of the time. :-)

Example:

[retrofox]

got it now!

[simison]

If I'm not wrong, you need to register the handler in the client, as core does when registering the core/post-meta handler here.

Thanks! Makes sense. I wonder if it would make sense for editor side to just handle that registration automatically, since all the information sort of exists in the backend binding already, and there's the concept of "backend rendered blocks" in the client side already. 🤔

[retrofox]

If I'm not wrong, you need to register the handler in the client, as core does when registering the core/post-meta handler here.

Thanks! Makes sense. I wonder if it would make sense for editor side to just handle that registration automatically, since all the information sort of exists in the backend binding already, and there's the concept of "backend rendered blocks" in the client side already. 🤔

Yeah, do you mean dynamic blocks? For instance, how does the core/post-title pull the data from the entity?
It would be nice when registering the source, the register_block_bindings_source() function accepts a parameter to always pull the data from the get_value_callback. Just thinking loud.

[github-actions]

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If this PR is still useful, please do a [trunk merge or rebase](https://github.com/Automattic/jetpack/blob/trunk/docs/git-workflow.md#keeping-your-branch-up-to-date) and otherwise make sure it's up to date and has clear testing instructions. You may also want to ping possible reviewers in case they've forgotten about it. Please close this PR if you think it's not valid anymore — if you do, please add a brief explanation.

If the PR is not updated (or at least commented on) in another month, it will be automatically closed.

[github-actions]

This PR has been marked as stale. This happened because:

• It has been inactive for the past 3 months.
• It hasn’t been labeled `[Pri] BLOCKER`, `[Pri] High`, etc.

If this PR is still useful, please do a [trunk merge or rebase](https://github.com/Automattic/jetpack/blob/trunk/docs/git-workflow.md#keeping-your-branch-up-to-date) and otherwise make sure it's up to date and has clear testing instructions. You may also want to ping possible reviewers in case they've forgotten about it. Please close this PR if you think it's not valid anymore — if you do, please add a brief explanation.

If the PR is not updated (or at least commented on) in another month, it will be automatically closed.