uniqueKeys property
Every unique index and constraint, the primary key included.
This is what tells a one-to-one from a one-to-many. Both are the same foreign key pointing here; the difference is whether the other side can hold more than one row per parent, and a unique constraint on its foreign key columns is exactly the guarantee that it cannot.
Filtered and disabled indexes are kept rather than dropped, because a caller has to be able to see that they exist and why they do not count — see MssqlUniqueKeySchema.guaranteesUniqueness.
Implementation
final List<MssqlUniqueKeySchema> uniqueKeys;