Allow fork choice to support multiple versions of a slot (#16266)

runtime/src/bank.rs

@@ -2127,6 +2127,10 @@ impl Bank {
         self.parent_slot
     }
 
+    pub fn parent_hash(&self) -> Hash {
+        self.parent_hash
+    }
+
     fn process_genesis_config(&mut self, genesis_config: &GenesisConfig) {
         // Bootstrap validator collects fees until `new_from_parent` is called.
         self.fee_rate_governor = genesis_config.fee_rate_governor.clone();

runtime/src/bank_forks.rs

@@ -6,7 +6,7 @@ use crate::{
 };
 use log::*;
 use solana_metrics::inc_new_counter_info;
-use solana_sdk::{clock::Slot, timing};
+use solana_sdk::{clock::Slot, hash::Hash, timing};
 use std::{
     collections::{hash_map::Entry, HashMap, HashSet},
     ops::Index,
@@ -106,6 +106,17 @@ impl BankForks {
         self.banks.get(&bank_slot)
     }
 
+    pub fn get_with_checked_hash(
+        &self,
+        (bank_slot, expected_hash): (Slot, Hash),
+    ) -> Option<&Arc<Bank>> {
+        let maybe_bank = self.banks.get(&bank_slot);
+        if let Some(bank) = maybe_bank {
+            assert_eq!(bank.hash(), expected_hash);
+        }
+        maybe_bank
+    }
+
     pub fn root_bank(&self) -> Arc<Bank> {
         self[self.root()].clone()
     }