feat(governance): clear voting power snapshots on Mission 70 activation

rs/nns/governance/src/governance.rs

@@ -8,6 +8,7 @@ use crate::{
             validate_merge_neurons_before_commit,
         },
         split_neuron::{SplitNeuronEffect, calculate_split_neuron_effect},
+        voting_power_snapshots::VotingPowerSnapshots,
     },
     heap_governance_data::{
         HeapGovernanceData, XdrConversionRate, initialize_governance, reassemble_governance_proto,
@@ -1355,6 +1356,8 @@ impl Governance {
             governance.heap_data.neuron_id_to_pre_clamp_dissolve_state = governance
                 .neuron_store
                 .clamp_dissolve_delay_for_all_neurons_or_panic(now);
+
+            VOTING_POWER_SNAPSHOTS.with_borrow_mut(VotingPowerSnapshots::clear);
         }
 
         governance

rs/nns/governance/src/governance/voting_power_snapshots.rs

@@ -5,7 +5,7 @@ use crate::{
     pb::v1::{Ballot, NeuronIdToVotingPowerMap, VotingPowerTotal},
 };
 
-use ic_cdk::eprintln;
+use ic_cdk::{eprintln, println};
 use ic_nervous_system_common::ONE_MONTH_SECONDS;
 use ic_stable_structures::{
     DefaultMemoryImpl, StableBTreeMap, Storable, memory_manager::VirtualMemory, storable::Bound,
@@ -202,6 +202,14 @@ impl VotingPowerSnapshots {
             voting_power_map,
             totals_with_minimum_total_potential_voting_power,
         ));
+        println!(
+            "{}Voting power spike detected at timestamp {}, total potential voting power: {}, \
+            minimum total potential voting power: {}",
+            LOG_PREFIX,
+            timestamp_with_minimum_total_potential_voting_power,
+            total_potential_voting_power,
+            totals_with_minimum_total_potential_voting_power.total_potential_voting_power
+        );
         Some((
             timestamp_with_minimum_total_potential_voting_power,
             previous_voting_power_snapshot,
@@ -214,6 +222,13 @@ impl VotingPowerSnapshots {
             .last_key_value()
             .map(|(timestamp, _)| timestamp)
     }
+
+    /// Clears the voting power snapshots.
+    // TODO(NNS1-4323): Remove this method after Mission 70 is fully deployed.
+    pub(crate) fn clear(&mut self) {
+        self.neuron_id_to_voting_power_maps.clear_new();
+        self.voting_power_totals.clear_new();
+    }
 }
 
 impl Storable for NeuronIdToVotingPowerMap {

rs/nns/governance/src/governance/voting_power_snapshots_tests.rs

@@ -113,3 +113,32 @@ fn test_record_voting_power_snapshot() {
         None,
     );
 }
+
+// TODO(NNS1-4323): Remove this test after Mission 70 is fully deployed.
+#[test]
+fn test_clear() {
+    let memory_manager = MemoryManager::init(DefaultMemoryImpl::default());
+    let mut snapshots = VotingPowerSnapshots::new(
+        memory_manager.get(MemoryId::new(0)),
+        memory_manager.get(MemoryId::new(1)),
+    );
+
+    // Record a few snapshots.
+    for i in 1..=3 {
+        snapshots.record_voting_power_snapshot(i, voting_power_snapshot(vec![90, 10], 100 + i));
+    }
+
+    // Verify that snapshots are present.
+    assert_eq!(snapshots.latest_snapshot_timestamp_seconds(), Some(3));
+
+    // Clear the snapshots.
+    snapshots.clear();
+
+    // Verify that everything is empty.
+    assert_eq!(snapshots.latest_snapshot_timestamp_seconds(), None);
+    assert_eq!(
+        snapshots.previous_ballots_if_voting_power_spike_detected(u64::MAX, 10),
+        None
+    );
+    assert!(!snapshots.is_latest_snapshot_a_spike(10));
+}