Fix Capella schema downgrades (#4004)

beacon_node/beacon_chain/src/schema_change/migration_schema_v14.rs

@@ -2,9 +2,41 @@ use crate::beacon_chain::{BeaconChainTypes, OP_POOL_DB_KEY};
 use operation_pool::{
     PersistedOperationPool, PersistedOperationPoolV12, PersistedOperationPoolV14,
 };
-use slog::{debug, info, Logger};
+use slog::{debug, error, info, Logger};
+use slot_clock::SlotClock;
 use std::sync::Arc;
+use std::time::Duration;
 use store::{Error, HotColdDB, KeyValueStoreOp, StoreItem};
+use types::{EthSpec, Hash256, Slot};
+
+/// The slot clock isn't usually available before the database is initialized, so we construct a
+/// temporary slot clock by reading the genesis state. It should always exist if the database is
+/// initialized at a prior schema version, however we still handle the lack of genesis state
+/// gracefully.
+fn get_slot_clock<T: BeaconChainTypes>(
+    db: &HotColdDB<T::EthSpec, T::HotStore, T::ColdStore>,
+    log: &Logger,
+) -> Result<Option<T::SlotClock>, Error> {
+    let spec = db.get_chain_spec();
+    let genesis_block = if let Some(block) = db.get_blinded_block(&Hash256::zero())? {
+        block
+    } else {
+        error!(log, "Missing genesis block");
+        return Ok(None);
+    };
+    let genesis_state =
+        if let Some(state) = db.get_state(&genesis_block.state_root(), Some(Slot::new(0)))? {
+            state
+        } else {
+            error!(log, "Missing genesis state"; "state_root" => ?genesis_block.state_root());
+            return Ok(None);
+        };
+    Ok(Some(T::SlotClock::new(
+        spec.genesis_slot,
+        Duration::from_secs(genesis_state.genesis_time()),
+        Duration::from_secs(spec.seconds_per_slot),
+    )))
+}
 
 pub fn upgrade_to_v14<T: BeaconChainTypes>(
     db: Arc<HotColdDB<T::EthSpec, T::HotStore, T::ColdStore>>,
@@ -41,17 +73,35 @@ pub fn downgrade_from_v14<T: BeaconChainTypes>(
     db: Arc<HotColdDB<T::EthSpec, T::HotStore, T::ColdStore>>,
     log: Logger,
 ) -> Result<Vec<KeyValueStoreOp>, Error> {
+    // We cannot downgrade from V14 once the Capella fork has been reached because there will
+    // be HistoricalSummaries stored in the database instead of HistoricalRoots and prior versions
+    // of Lighthouse can't handle that.
+    if let Some(capella_fork_epoch) = db.get_chain_spec().capella_fork_epoch {
+        let current_epoch = get_slot_clock::<T>(&db, &log)?
+            .and_then(|clock| clock.now())
+            .map(|slot| slot.epoch(T::EthSpec::slots_per_epoch()))
+            .ok_or(Error::SlotClockUnavailableForMigration)?;
+
+        if current_epoch >= capella_fork_epoch {
+            error!(
+                log,
+                "Capella already active: v14+ is mandatory";
+                "current_epoch" => current_epoch,
+                "capella_fork_epoch" => capella_fork_epoch,
+            );
+            return Err(Error::UnableToDowngrade);
+        }
+    }
+
     // Load a V14 op pool and transform it to V12.
-    let PersistedOperationPoolV14 {
+    let PersistedOperationPoolV14::<T::EthSpec> {
         attestations,
         sync_contributions,
         attester_slashings,
         proposer_slashings,
         voluntary_exits,
         bls_to_execution_changes,
-    } = if let Some(PersistedOperationPool::<T::EthSpec>::V14(op_pool)) =
-        db.get_item(&OP_POOL_DB_KEY)?
-    {
+    } = if let Some(op_pool) = db.get_item(&OP_POOL_DB_KEY)? {
         op_pool
     } else {
         debug!(log, "Nothing to do, no operation pool stored");

beacon_node/beacon_chain/src/schema_change/migration_schema_v15.rs

@@ -43,7 +43,7 @@ pub fn downgrade_from_v15<T: BeaconChainTypes>(
     log: Logger,
 ) -> Result<Vec<KeyValueStoreOp>, Error> {
     // Load a V15 op pool and transform it to V14.
-    let PersistedOperationPoolV15 {
+    let PersistedOperationPoolV15::<T::EthSpec> {
         attestations,
         sync_contributions,
         attester_slashings,
@@ -51,9 +51,7 @@ pub fn downgrade_from_v15<T: BeaconChainTypes>(
         voluntary_exits,
         bls_to_execution_changes,
         capella_bls_change_broadcast_indices,
-    } = if let Some(PersistedOperationPool::<T::EthSpec>::V15(op_pool)) =
-        db.get_item(&OP_POOL_DB_KEY)?
-    {
+    } = if let Some(op_pool) = db.get_item(&OP_POOL_DB_KEY)? {
         op_pool
     } else {
         debug!(log, "Nothing to do, no operation pool stored");