Bugfix: slots_connected snapshot_slot not full (#26506)

* slots_connected check used by ledger-tool should not require a full slot for snapshot slot

* Cleaner Result<Option<>> unwrap/default

* return false if no meta for starting slot

* Add clarifying comments

ledger-tool/src/main.rs

@@ -798,6 +798,8 @@ fn load_bank_forks(
     };
 
     if let Some(halt_slot) = process_options.halt_at_slot {
+        // Check if we have the slot data necessary to replay from starting_slot to halt_slot.
+        //  - This will not catch the case when loading from genesis without a full slot 0.
         if !blockstore.slots_connected(starting_slot, halt_slot) {
             eprintln!(
                 "Unable to load bank forks at slot {} due to disconnected blocks.",

ledger/src/blockstore.rs

@@ -547,9 +547,17 @@ impl Blockstore {
         self.prepare_rooted_slot_iterator(slot, IteratorDirection::Reverse)
     }
 
-    /// Determines if starting_slot and ending_slot are connected
+    /// Determines if `starting_slot` and `ending_slot` are connected by full slots
+    /// `starting_slot` is excluded from the `is_full()` check
     pub fn slots_connected(&self, starting_slot: Slot, ending_slot: Slot) -> bool {
-        let mut next_slots: VecDeque<_> = vec![starting_slot].into();
+        if starting_slot == ending_slot {
+            return true;
+        }
+
+        let mut next_slots: VecDeque<_> = match self.meta(starting_slot) {
+            Ok(Some(starting_slot_meta)) => starting_slot_meta.next_slots.into(),
+            _ => return false,
+        };
         while let Some(slot) = next_slots.pop_front() {
             if let Ok(Some(slot_meta)) = self.meta(slot) {
                 if slot_meta.is_full() {
@@ -4354,6 +4362,16 @@ pub mod tests {
         entries
     }
 
+    fn make_and_insert_slot(blockstore: &Blockstore, slot: Slot, parent_slot: Slot) {
+        let (shreds, _) = make_slot_entries(slot, parent_slot, 100);
+        blockstore.insert_shreds(shreds, None, true).unwrap();
+
+        let meta = blockstore.meta(slot).unwrap().unwrap();
+        assert_eq!(slot, meta.slot);
+        assert!(meta.is_full());
+        assert!(meta.next_slots.is_empty());
+    }
+
     #[test]
     fn test_create_new_ledger() {
         solana_logger::setup();
@@ -5489,13 +5507,7 @@ pub mod tests {
 
         let num_slots = 3;
         for slot in 1..=num_slots {
-            let (shreds, _) = make_slot_entries(slot, slot.saturating_sub(1), 100);
-            blockstore.insert_shreds(shreds, None, true).unwrap();
-
-            let meta = blockstore.meta(slot).unwrap().unwrap();
-            assert_eq!(slot, meta.slot);
-            assert!(meta.is_full());
-            assert!(meta.next_slots.is_empty());
+            make_and_insert_slot(&blockstore, slot, slot.saturating_sub(1));
         }
 
         assert!(blockstore.slots_connected(1, 3));
@@ -5507,16 +5519,6 @@ pub mod tests {
         let ledger_path = get_tmp_ledger_path_auto_delete!();
         let blockstore = Blockstore::open(ledger_path.path()).unwrap();
 
-        fn make_and_insert_slot(blockstore: &Blockstore, slot: Slot, parent_slot: Slot) {
-            let (shreds, _) = make_slot_entries(slot, parent_slot, 100);
-            blockstore.insert_shreds(shreds, None, true).unwrap();
-
-            let meta = blockstore.meta(slot).unwrap().unwrap();
-            assert_eq!(slot, meta.slot);
-            assert!(meta.is_full());
-            assert!(meta.next_slots.is_empty());
-        }
-
         make_and_insert_slot(&blockstore, 1, 0);
         make_and_insert_slot(&blockstore, 2, 1);
         make_and_insert_slot(&blockstore, 4, 2);
@@ -5525,6 +5527,26 @@ pub mod tests {
         assert!(blockstore.slots_connected(1, 4));
     }
 
+    #[test]
+    fn test_slots_connected_same_slot() {
+        let ledger_path = get_tmp_ledger_path_auto_delete!();
+        let blockstore = Blockstore::open(ledger_path.path()).unwrap();
+
+        assert!(blockstore.slots_connected(54, 54));
+    }
+
+    #[test]
+    fn test_slots_connected_starting_slot_not_full() {
+        let ledger_path = get_tmp_ledger_path_auto_delete!();
+        let blockstore = Blockstore::open(ledger_path.path()).unwrap();
+
+        make_and_insert_slot(&blockstore, 5, 4);
+        make_and_insert_slot(&blockstore, 6, 5);
+
+        assert!(!blockstore.meta(4).unwrap().unwrap().is_full());
+        assert!(blockstore.slots_connected(4, 6));
+    }
+
     #[test]
     fn test_get_slots_since() {
         let ledger_path = get_tmp_ledger_path_auto_delete!();