Differentiate unsupported blocks from unavailable

[koke]

Turning unrecognized blocks (markup that doesn’t match any of the registered blocks) is the easy part. We also need to identify which blocks are available on the server but don't have a mobile implementation yet.

When the block doesn't exist on the server, we should use a UI similar to the one in WordPress/gutenberg#8274 saying that the site doesn't support that block.

However when it's just not supported on mobile the UI should be different.

To avoid confusion, let's use this terminology unless/until we agree on a new one:

• Unregistered block: A block that has valid syntax but it's not registered on the server (e.g. a block provided by a plugin that was uninstalled)
• Unsupported block: A block that is valid on the server and will render correctly, but doesn't have a working mobile implementation.

Right now I anticipate we'll need:

• Review the UI design for both states (@iamthomasbishop).
• Start by assuming all core blocks are registered even if they are unsupported.
• Implement the new UI for both cases.
• Figure out if there is an API to query what blocks are registered (WIP:
  Expose available blocks via an API WordPress/gutenberg#4116), and what we need to support that (like WP-API support)

[diegoreymendez]

I'd suggest the API thing should go first, since it's basically a requirement to implement this feature.

[koke]

@hypest do you know if there is such an API? Can we make that happen so it's ready for Q1?

[koke]

The API (WordPress/gutenberg#4116) is not ready yet, and I can't bet sure it will be in 5.0. I don't think there's much to do here if we can't differentiate so I'm postponing this one until we have an API, and we'll just improve styling of the existing unsupported block.

[hypest]

so I'm postponing this one until we have an API

Sorry I missed the ping earlier. This sounds good to me 👍

[hypest]

Putting this on the Backlog and we can revisit if the (ongoing at the time of writing) "Unsupported Blocks Fallback" project is not helping with this. cc @iamthomasbishop