POC: Use Block bindings API with existing post_meta

[carstingaxion]

Similar to #330 I wanted to validate my ideas on data-migration.

Today: The new Block bindings API connected to existing post_meta.

This should help migrating the existing shortcodes, which use some special template tags like {{duration}} to display post_meta. I did bind the post_meta field of remark to a new core block variation, and it worked really well.

Ressources

• Block Bindings API iteration for 6.5 WordPress/gutenberg#54536
• Block Bindings API: Add block bindings PHP registration mechanisms and "Post meta" source under the experimental flag WordPress/gutenberg#57249
• Block Bindings API (part 2) and custom sources WordPress/developer-blog-content#225

Steps I took

• Update to WP 6.5 beta 1
• Change register_post_type arguments of wp_theatre_prod to support `'custom-fields'
• Change register_post_meta to include 'show_in_rest' following the Testing Instructions
• Just add the markup into the editor

<!-- wp:paragraph {"metadata":{"bindings":{"content":{"source":"core/post-meta","args":{"key":"remark"}}}}} -->
<p>Paragraph</p>
<!-- /wp:paragraph -->

This worked really well.

To make this a little easier to recognize for the editor I created a simple block-variation of the paragraph block to hold the markup I added by hand in the step before. This block variation even allowed me to define a custom name and icon, which was nice.

Block variations could be one way to go to properly migrate into the new era. You can give it a try and have a look through the code at https://github.com/figuren-theater/theater-production-blocks/tree/feature/wpt-shortcode-to-query-block

some findings to feed back to the gutenberg contributors

• Transforming a paragraph into a headline erases all relevant block attributes, which is a known issue
• adding the attributes to registerBlockVariation() fails, because 'metadata' is undefined; 🐛 maybe this is no properly registered attribute