The update breaks an existing test which passes to dbQuoteIdentifier an Id object with a schema name and no table. The resulting SQL string has the form "schema_name"., which does not conform to the dbQuoteIdentifier() spec's requirement that the result be suitable as a table or column name. The new dbUnquoteIdentifier() rejects this as an illegal SQL expression (correctly), but this does mean that a dbQuoteIdentifier()/dbUnquoteIdentifier() round trip for an arbitrary Id object is not guaranteed.

I would argue that the new behavior is correct, given the spec for dbQuoteIdentifier(). If so, the fix is to change the list_objects_features test in spec-sql-list-objects.R to attempt quoting/unquoting only objects that have a table name (i.e. is_prefix is false).

If the preference is to retain the roundtrip rather than a valid SQL expression, the fix is to change the regex in dbUnquoteIdentifier() to accept zero or more characters after a . rather than 1 or more.