How URI resolution will work if $id keyword is an empty string? Or if multiple schemas have the same canonical URI?

[flaksp]

Seems like $id may be an empty string:

"uriReferenceString": {
  "type": "string",
  "format": "uri-reference"
}

So, this document contains 2 schemas:

{
  "$id": "https://example.com/Foo",
  "$defs": {
    "bar": {
      "$id": ""
    }
  }
}

Does https://example.com/Foo references the root schema or the bar schema? What behaviour should be if multiple schemas have the same canonical URI?

[handrews]

"" is a relative URI-reference with a path component consisting of an empty string. Setting "$id": "" like this is technically an error in accordance with §9.1.2:

A schema MAY (and likely will) have multiple URIs, but there is no way for a URI to identify more than one schema. When multiple schemas try to identify as the same URI, validators SHOULD raise an error condition.

because resolving "" against the base URI of ""https://example.com/Foo" just produces "https://example.com/Foo" again, meaning that both of these "$id"s attempt to assign the same URI to two different schemas.

[handrews]

This was recently somewhat clarified by issue json-schema-org/json-schema-spec#1271 and PR json-schema-org/json-schema-spec#1272, BTW.