Faster joins: check compatibility with history import

[richvdh]

I suspect the MSC2716 code makes incorrect assumptions about whether state is complete at the insertion points.

synapse/synapse/handlers/federation_event.py

Lines 778 to 785 in 7c6b220

	state_ids = await self._resolve_state_at_missing_prevs(origin, event)
	# TODO(faster_joins): make sure that _resolve_state_at_missing_prevs does
	# not return partial state
	# https://github.com/matrix-org/synapse/issues/13002
	await self._process_received_pdu(
	origin, event, state_ids=state_ids, backfilled=backfilled
	)

[richvdh]

cc @MadLittleMods

[MadLittleMods]

Maybe. We need the full state at the event you insert next to (the /batch_send?prev_event_id) to inherit from. See:

• synapse/rest/client/room_batch.py#L139-L145
• synapse/handlers/room_batch.py#L125-L150 -> get_most_recent_full_state_ids_from_event_id_list

[richvdh]

We should just disallow history import for partial-state rooms