Add option to filter specific blocks to specific widget areas

[myleshyson]

What problem does this address?

I would like to filter what blocks are available on a per widget area basis. Currently there doesn't seem to be a way to do this.

What is your proposed solution?

Something like this would be ideal

register_sidebar( [
    'name'            => __( 'Primary Sidebar', 'theme_name' ),
    'allowed_blocks'  => [ 'core/paragraph', 'core/latest-posts' ]
] );

[myleshyson]

This is related to #28517, and and I'm wondering if this should be included along with that issue?

For more context, this is important for us because some blocks don't make sense for certain contexts. For example, the columns block makes sense for a Footer widget area, but definitely should not be allowed for a Post Sidebar widget area. We need a way to force those distinctions for our editors.

[noisysocks]

Grea idea. Let's include it as part of #28517 so that there isn't too many issues floating around. I'll copy your suggestion in there.

[noisysocks]

Reopening this as #28517 didn't add the exact API proposed here.

[cr0ybot]

I'm completely failing at finding a workaround to this problem, the proposed API in register_sidebar with allowed_blocks looks rad. I'm particularly keen on creating a Social widget area that only allows the social-links and social-link blocks so that I can output a site's social media links/icons in different places while keeping the data to one source of truth.