Merge branch 'jason/NNS1-2935-8' into 'master'

refactor(nns): NNS1-2935 Make neuron state & age fields private

We'd like to make neuron state & age fields private so that the relevant invariants can be guaranteed

Closes NNS1-2935 

Closes NNS1-2935

See merge request dfinity-lab/public/ic!19056

rs/nns/governance/src/neuron/dissolve_state_and_age.rs

@@ -113,6 +113,28 @@ impl DissolveStateAndAge {
         }
     }
 
+    /// Returns the timestamp when the neuron will be dissolved. If the neuron is not dissolving, it
+    /// returns None. Note that when self == LegacyDissolved {..}, even though the Neuron is
+    /// dissolved, we do not know when that happened. This tends to happen when Neurons are first
+    /// created. We will clean up this case soon.
+    pub fn dissolved_at_timestamp_seconds(self) -> Option<u64> {
+        match self {
+            Self::NotDissolving { .. } => None,
+            Self::DissolvingOrDissolved {
+                when_dissolved_timestamp_seconds,
+            } => Some(when_dissolved_timestamp_seconds),
+            Self::LegacyDissolvingOrDissolved {
+                when_dissolved_timestamp_seconds,
+                ..
+            } => Some(when_dissolved_timestamp_seconds),
+            // The dissolved neurons in this case have DissolveDelaySeconds(0), which are created
+            // when the neurons are first claimed. We don't know exactly when they are dissolved
+            // from their dissolve state.
+            Self::LegacyDissolved { .. } => None,
+            Self::LegacyNoneDissolveState { .. } => None,
+        }
+    }
+
     /// Increases the dissolve delay of the neuron by the given number of seconds. If the neuron is
     /// already dissolved, it transitions to a non-dissolving state with the new dissolve delay. If
     /// the neuron is dissolving, the dissolve timestamp is increased by the given number of

rs/nns/governance/src/neuron/mod.rs

@@ -769,27 +769,8 @@ impl Neuron {
     /// WhenDissolvedTimestampSeconds(now()), but we didn't. This could be changed for new Neurons,
     /// but there is no intention to do that (yet).
     pub fn dissolved_at_timestamp_seconds(&self) -> Option<u64> {
-        use DissolveState::{DissolveDelaySeconds, WhenDissolvedTimestampSeconds};
-        match self.dissolve_state {
-            None => None,
-            Some(WhenDissolvedTimestampSeconds(result)) => Some(result),
-            Some(DissolveDelaySeconds(_)) => None,
-        }
-    }
-
-    /// Returns an enum representing the dissolve state and age of a neuron.
-    pub fn dissolve_state_and_age(&self) -> DissolveStateAndAge {
-        DissolveStateAndAge::from(StoredDissolvedStateAndAge {
-            dissolve_state: self.dissolve_state.clone(),
-            aging_since_timestamp_seconds: self.aging_since_timestamp_seconds,
-        })
-    }
-
-    /// Sets a neuron's dissolve state and age.
-    pub fn set_dissolve_state_and_age(&mut self, state_and_age: DissolveStateAndAge) {
-        let stored = StoredDissolvedStateAndAge::from(state_and_age);
-        self.dissolve_state = stored.dissolve_state;
-        self.aging_since_timestamp_seconds = stored.aging_since_timestamp_seconds;
+        self.dissolve_state_and_age()
+            .dissolved_at_timestamp_seconds()
     }
 
     pub fn subtract_staked_maturity(&mut self, amount_e8s: u64) {

rs/nns/governance/src/neuron/types.rs

@@ -60,7 +60,7 @@ pub struct Neuron {
     /// This value is meaningless when the neuron is dissolving, since a
     /// dissolving neurons always has age zero. The canonical value of
     /// this field for a dissolving neuron is `u64::MAX`.
-    pub aging_since_timestamp_seconds: u64,
+    aging_since_timestamp_seconds: u64,
     /// The timestamp, in seconds from the Unix epoch, at which this
     /// neuron should be spawned and its maturity converted to ICP
     /// according to <https://wiki.internetcomputer.org/wiki/Maturity_modulation.>
@@ -120,7 +120,7 @@ pub struct Neuron {
     /// (b) `dissolve_delay` is set to zero, (c) neither value is set.
     ///
     /// Cf. \[Neuron::stop_dissolving\] and \[Neuron::start_dissolving\].
-    pub dissolve_state: Option<NeuronDissolveState>,
+    dissolve_state: Option<NeuronDissolveState>,
 }
 
 impl Neuron {
@@ -144,6 +144,21 @@ impl Neuron {
         self.controller = new_controller;
     }
 
+    /// Returns an enum representing the dissolve state and age of a neuron.
+    pub fn dissolve_state_and_age(&self) -> DissolveStateAndAge {
+        DissolveStateAndAge::from(StoredDissolvedStateAndAge {
+            dissolve_state: self.dissolve_state.clone(),
+            aging_since_timestamp_seconds: self.aging_since_timestamp_seconds,
+        })
+    }
+
+    /// Sets a neuron's dissolve state and age.
+    pub fn set_dissolve_state_and_age(&mut self, state_and_age: DissolveStateAndAge) {
+        let stored = StoredDissolvedStateAndAge::from(state_and_age);
+        self.dissolve_state = stored.dissolve_state;
+        self.aging_since_timestamp_seconds = stored.aging_since_timestamp_seconds;
+    }
+
     /// Returns the dissolve state. Deprecated and only used by the old merge neurons flow and will
     /// be cleaned up.
     pub fn depregated_dissolve_state(&self) -> Option<NeuronDissolveState> {