Fix the bug

Pruning stopped short of pruning the entire abandoned chain. It only
pruned the head.  This has to do with get_state() returning unexpected
states based on slots for states that that lie below the "split point".
Fix by doing pruning on the hot database (as it should be from the
start) and not touching the cold database.

beacon_node/beacon_chain/src/migrate.rs

@@ -202,11 +202,6 @@ impl<E: EthSpec, Hot: ItemStore<E>, Cold: ItemStore<E>> Migrate<E, Hot, Cold>
         old_finalized_block_hash: SignedBeaconBlockHash,
         new_finalized_block_hash: SignedBeaconBlockHash,
     ) {
-        if let Err(e) = process_finalization(self.db.clone(), state_root, &new_finalized_state) {
-            // This migrator is only used for testing, so we just log to stderr without a logger.
-            eprintln!("Migration error: {:?}", e);
-        }
-
         if let Err(e) = Self::prune_abandoned_forks(
             self.db.clone(),
             head_tracker,
@@ -216,6 +211,11 @@ impl<E: EthSpec, Hot: ItemStore<E>, Cold: ItemStore<E>> Migrate<E, Hot, Cold>
         ) {
             eprintln!("Pruning error: {:?}", e);
         }
+
+        if let Err(e) = process_finalization(self.db.clone(), state_root, &new_finalized_state) {
+            // This migrator is only used for testing, so we just log to stderr without a logger.
+            eprintln!("Migration error: {:?}", e);
+        }
     }
 }
 
@@ -325,6 +325,17 @@ impl<E: EthSpec, Hot: ItemStore<E>, Cold: ItemStore<E>> BackgroundMigrator<E, Ho
                 new_finalized_slot,
             )) = rx.recv()
             {
+                match Self::prune_abandoned_forks(
+                    db.clone(),
+                    head_tracker,
+                    old_finalized_block_hash,
+                    new_finalized_block_hash,
+                    new_finalized_slot,
+                ) {
+                    Ok(()) => {}
+                    Err(e) => warn!(log, "Block pruning failed: {:?}", e),
+                }
+
                 match process_finalization(db.clone(), state_root, &state) {
                     Ok(()) => {}
                     Err(Error::HotColdDBError(HotColdDBError::FreezeSlotUnaligned(slot))) => {
@@ -342,17 +353,6 @@ impl<E: EthSpec, Hot: ItemStore<E>, Cold: ItemStore<E>> BackgroundMigrator<E, Ho
                         );
                     }
                 };
-
-                match Self::prune_abandoned_forks(
-                    db.clone(),
-                    head_tracker,
-                    old_finalized_block_hash,
-                    new_finalized_block_hash,
-                    new_finalized_slot,
-                ) {
-                    Ok(()) => {}
-                    Err(e) => warn!(log, "Block pruning failed: {:?}", e),
-                }
             }
         });