Preloaded toot: context defines attributionDomains as an IRI #1233

The preloaded JSON-LD context for http://joinmastodon.org/ns in packages/vocab-runtime/src/contexts/joinmastodon.json defines attributionDomains with "@type": "@id". Mastodon defines the same term in app/helpers/context_helper.rb as:

{
  "attributionDomains": {
    "@id": "toot:attributionDomains",
    "@container": "@set"
  }
}

The values are plain domain names such as "blog.example", not IRIs. With Fedify's definition, a document that relies on the preloaded context expands them as node references instead of string literals.

The bug has been present since the context was added in 2.0.6 (c7c2048).

Reproduction

Expand this document with jsonld and Fedify's preloaded contexts:

{
  "@context": [
    "https://www.w3.org/ns/activitystreams",
    "http://joinmastodon.org/ns"
  ],
  "id": "https://social.example/users/alice",
  "type": "Person",
  "attributionDomains": ["blog.example"]
}

Expected, matching Mastodon's definition:

"http://joinmastodon.org/ns#attributionDomains": [{ "@value": "blog.example" }]

Actual:

"http://joinmastodon.org/ns#attributionDomains": [{ "@id": "blog.example" }]

"blog.example" is a relative IRI here, so a processor resolves it against the document base or drops it, and the RDF no longer matches what Mastodon means.

Fix

Replace "@type": "@id" with "@container": "@set" in joinmastodon.json and add a regression test for the expansion above.