Log about multiple roots in dag tree

Author: dapplion

beacon_node/beacon_chain/src/migrate.rs

@@ -546,6 +546,17 @@ impl<E: EthSpec, Hot: ItemStore<E>, Cold: ItemStore<E>> BackgroundMigrator<E, Ho
             )
         };
 
+        // To debug faulty trees log unexpected that have more than one root. These trees may not
+        // result in an error, as may not be queried in the codepaths below.
+        let state_summaries_dag_roots = state_summaries_dag.tree_roots();
+        if state_summaries_dag_roots.len() > 1 {
+            warn!(
+                log,
+                "Prune state summaries dag found more than one root";
+                "state_summaries_dag_roots" => ?state_summaries_dag_roots
+            );
+        }
+
         // From the DAG compute the list of roots that descend from finalized root up to the
         // split slot.
 

beacon_node/beacon_chain/src/summaries_dag.rs

@@ -139,6 +139,22 @@ impl StateSummariesDAG {
         Ok(Self::new(state_summaries))
     }
 
+    /// Returns a vec of state summaries that have an unknown parent when forming the DAG tree
+    pub fn tree_roots(&self) -> Vec<(Hash256, DAGStateSummary)> {
+        self.state_summaries_by_block_root
+            .values()
+            .flat_map(|summaries| {
+                summaries.values().filter_map(|(state_root, summary)| {
+                    if summary.previous_state_root == Hash256::ZERO {
+                        Some((*state_root, *summary))
+                    } else {
+                        None
+                    }
+                })
+            })
+            .collect()
+    }
+
     pub fn summaries_count(&self) -> usize {
         self.state_summaries_by_block_root
             .values()