chore(runtime): Adjust target inflation value

pallets/staking-rewards/src/inflation.rs

@@ -118,10 +118,10 @@ mod test {
     }
 
     static TTS: u128 = 10_000_000_000;
-    static STAKEABLE: u128 = 4_250_000_000; // 42.5% of TTS
+    static STAKEABLE: u128 = 4_849_000_000; // 48.49% of TTS
     static IDEAL_STAKE: Perquintill = Perquintill::from_percent(85);
     static MIN_INFLATION: Perquintill = Perquintill::from_percent(1);
-    static MAX_INFLATION: Perquintill = Perquintill::from_parts(57_800_000_000_000_000_u64); // 5.78%
+    static MAX_INFLATION: Perquintill = Perquintill::from_parts(60_000_000_000_000_000_u64); // 6.00%
     static FALLOFF: Perquintill = Perquintill::from_percent(2);
     static MAX_ROI: Perquintill = Perquintill::from_percent(30);
     static MILLISECONDS_PER_YEAR: u64 = 1000 * 3600 * 24 * 36525 / 100;
@@ -136,26 +136,26 @@ mod test {
 
         let expected_payouts = vec![
             (0, 100_000_000),
-            (63_750_000, 64_367_647),
-            (127_500_000, 28_735_294),
-            (184_352_941, 0),
-            (212_470_588, 0),
-            (240_588_235, 0),
-            (268_705_882, 0),
-            (296_823_529, 0),
-            (324_941_176, 0),
-            (353_058_824, 0),
-            (381_176_471, 0),
-            (409_294_118, 0),
-            (437_411_765, 0),
-            (465_529_412, 0),
-            (493_647_059, 0),
-            (521_764_706, 0),
-            (549_882_353, 0),
-            (578_000_000, 0),
-            (184_499_260, 0),
-            (114_937_500, 0),
-            (102_640_602, 0),
+            (72_735_000, 56_676_765),
+            (145_470_000, 13_353_529),
+            (188_235_294, 0),
+            (217_647_059, 0),
+            (247_058_824, 0),
+            (276_470_588, 0),
+            (305_882_353, 0),
+            (335_294_118, 0),
+            (364_705_882, 0),
+            (394_117_647, 0),
+            (423_529_412, 0),
+            (452_941_176, 0),
+            (482_352_941, 0),
+            (511_764_706, 0),
+            (541_176_471, 0),
+            (570_588_235, 0),
+            (600_000_000, 0),
+            (188_388_348, 0),
+            (115_625_000, 0),
+            (102_762_136, 0),
         ];
         assert_eq!(staked.len(), expected_payouts.len());
 
@@ -188,26 +188,26 @@ mod test {
 
         let expected_payouts = vec![
             (0, 273_785),
-            (174_538, 176_229),
-            (349_076, 78_673),
-            (504_731, 0),
-            (581_713, 0),
-            (658_695, 0),
-            (735_677, 0),
-            (812_659, 0),
-            (889_640, 0),
-            (966_622, 0),
-            (1_043_604, 0),
-            (1_120_586, 0),
-            (1_197_568, 0),
-            (1_274_550, 0),
-            (1_351_532, 0),
-            (1_428_514, 0),
-            (1_505_496, 0),
-            (1_582_478, 0),
-            (505_131, 0),
-            (314_682, 0),
-            (281_015, 0),
+            (199_138, 155_172),
+            (398_275, 36_560),
+            (515_360, 0),
+            (595_885, 0),
+            (676_410, 0),
+            (756_935, 0),
+            (837_460, 0),
+            (917_985, 0),
+            (998_510, 0),
+            (1_079_035, 0),
+            (1_159_560, 0),
+            (1_240_085, 0),
+            (1_320_610, 0),
+            (1_401_135, 0),
+            (1_481_660, 0),
+            (1_562_185, 0),
+            (1_642_710, 0),
+            (515_779, 0),
+            (316_564, 0),
+            (281_347, 0),
         ];
         assert_eq!(staked.len(), expected_payouts.len());
 
@@ -239,27 +239,27 @@ mod test {
             .collect::<Vec<_>>();
 
         let expected_payouts = vec![
-            (0, 45_631),
-            (29_090, 29_372),
-            (58_179, 13_112),
-            (84_122, 0),
-            (96_952, 0),
-            (109_782, 0),
-            (122_613, 0),
-            (135_443, 0),
-            (148_273, 0),
-            (161_104, 0),
-            (173_934, 0),
-            (186_764, 0),
-            (199_595, 0),
-            (212_425, 0),
-            (225_255, 0),
-            (238_086, 0),
-            (250_916, 0),
-            (263_746, 0),
-            (84_189, 0),
-            (52_447, 0),
-            (46_836, 0),
+            (0, 45_630),
+            (33_189, 25_862),
+            (66_379, 6_093),
+            (85_893, 0),
+            (99_314, 0),
+            (112_735, 0),
+            (126_155, 0),
+            (139_576, 0),
+            (152_997, 0),
+            (166_418, 0),
+            (179_839, 0),
+            (193_260, 0),
+            (206_680, 0),
+            (220_101, 0),
+            (233_522, 0),
+            (246_943, 0),
+            (260_364, 0),
+            (273_785, 0),
+            (85_963, 0),
+            (52_760, 0),
+            (46_891, 0),
         ];
         assert_eq!(staked.len(), expected_payouts.len());
 

pallets/staking-rewards/src/lib.rs

@@ -86,7 +86,7 @@ pub mod pallet {
     use frame_system::pallet_prelude::*;
 
     /// The current storage version.
-    const STORAGE_VERSION: StorageVersion = StorageVersion::new(1);
+    const STORAGE_VERSION: StorageVersion = StorageVersion::new(2);
 
     #[pallet::pallet]
     #[pallet::storage_version(STORAGE_VERSION)]
@@ -367,19 +367,22 @@ impl<T: Config> OnUnbalanced<PositiveImbalanceOf<T>> for Pallet<T> {
     fn on_nonzero_unbalanced(minted: PositiveImbalanceOf<T>) {
         let amount = minted.peek();
 
-        let burned = T::Currency::withdraw(
+        if let Ok(burned) = T::Currency::withdraw(
             &Self::account_id(),
             amount,
             WithdrawReasons::TRANSFER,
             ExistenceRequirement::KeepAlive,
-        )
-        .unwrap_or_else(|_| NegativeImbalanceOf::<T>::zero());
-
-        // Offsetting rewards against rewards pool until the latter is not depleted.
-        // After that the positive imbalance is dropped adding up to the total supply.
-        let _ = minted.offset(burned);
-
-        Self::deposit_event(Event::Burned { amount });
+        ) {
+            // Offsetting rewards against rewards pool until the latter is not depleted.
+            // After that the positive imbalance is dropped adding up to the total supply.
+            let _ = minted.offset(burned);
+
+            Self::deposit_event(Event::Burned { amount });
+        } else {
+            log::warn!(
+                "Staking rewards pool has insufficient balance to burn minted rewards. The currency total supply may grow."
+            );
+        };
     }
 }
 

pallets/staking-rewards/src/migration.rs

@@ -16,14 +16,87 @@
 // You should have received a copy of the GNU General Public License
 // along with this program. If not, see <https://www.gnu.org/licenses/>.
 
-use crate::{Config, Pallet, Weight};
+use crate::{pallet, Config, Pallet, Weight};
+use frame_support::traits::{Get, GetStorageVersion, OnRuntimeUpgrade};
+use sp_runtime::Perquintill;
+use sp_std::marker::PhantomData;
 
-/// Wrapper for all migrations of this pallet, based on `StorageVersion`.
-pub fn migrate<T: Config>() -> Weight {
-    use frame_support::traits::GetStorageVersion;
+pub struct MigrateToV2<T: Config>(PhantomData<T>);
 
-    let _onchain = Pallet::<T>::on_chain_storage_version();
-    let weight: Weight = Weight::zero();
+impl<T: Config> OnRuntimeUpgrade for MigrateToV2<T> {
+    fn on_runtime_upgrade() -> Weight {
+        let current = Pallet::<T>::current_storage_version();
+        let onchain = Pallet::<T>::on_chain_storage_version();
 
-    weight
+        log::info!(
+            "🚚 Running migration with current storage version {:?} / onchain {:?}",
+            current,
+            onchain
+        );
+
+        let mut weight = T::DbWeight::get().reads(1); // 1 read for on chain storage version.
+
+        if current == 2 && onchain == 1 {
+            // Adjusted target inflation parameter: 6.00%
+            let adjusted_inflation: Perquintill = Perquintill::from_percent(6);
+            pallet::TargetInflation::<T>::put(adjusted_inflation);
+
+            current.put::<Pallet<T>>();
+
+            log::info!("Successfully migrated storage from v1 to v2");
+
+            // 1 write for `TargetInflation`
+            weight += T::DbWeight::get().writes(1)
+        } else {
+            log::info!("❌ Migration did not execute. This probably should be removed");
+        }
+
+        weight
+    }
+
+    #[cfg(feature = "try-runtime")]
+    fn pre_upgrade() -> Result<Vec<u8>, &'static str> {
+        use parity_scale_codec::Encode;
+
+        let inflation = pallet::TargetInflation::<T>::get();
+        assert_eq!(inflation, Perquintill::from_rational(578_u64, 10_000_u64));
+        Ok(inflation.encode())
+    }
+
+    #[cfg(feature = "try-runtime")]
+    fn post_upgrade(state: Vec<u8>) -> Result<(), &'static str> {
+        use parity_scale_codec::Decode;
+
+        let inflation: Perquintill = Decode::decode(&mut &state[..]).unwrap();
+        assert_eq!(inflation, Perquintill::from_percent(6),);
+        Ok(())
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::mock::*;
+    use frame_support::traits::StorageVersion;
+
+    #[test]
+    fn migrate_to_v2() {
+        ExtBuilder::default()
+            .initial_authorities(vec![(VAL_1_STASH, VAL_1_CONTROLLER, VAL_1_AUTH_ID)])
+            .stash(VALIDATOR_STAKE)
+            .endowment(ENDOWMENT)
+            .target_inflation(Perquintill::from_rational(578_u64, 10_000_u64))
+            .build()
+            .execute_with(|| {
+                StorageVersion::new(1).put::<Pallet<Test>>();
+
+                let weight = MigrateToV2::<Test>::on_runtime_upgrade();
+                assert_ne!(weight.ref_time(), 0);
+
+                assert_eq!(
+                    pallet::TargetInflation::<Test>::get(),
+                    Perquintill::from_percent(6),
+                );
+            })
+    }
 }

pallets/staking-rewards/src/tests.rs

@@ -1183,6 +1183,57 @@ fn unclaimed_rewards_burn() {
     });
 }
 
+#[test]
+fn empty_rewards_pool_causes_inflation() {
+    let (target_inflation, ideal_stake, _, non_stakeable) = sensible_defaults();
+    let pool_balance = 0; // empty rewards pool
+    let mut ext = with_parameters(target_inflation, ideal_stake, pool_balance, non_stakeable);
+    ext.execute_with(|| {
+        // Getting up-to-date data on era duration (they may differ from runtime constants)
+        let sessions_per_era = <Test as pallet_staking::Config>::SessionsPerEra::get() as u64;
+        let epoch_duration = SESSION_DURATION;
+        let era_duration = sessions_per_era * epoch_duration;
+
+        let (initial_total_issuance, _, _, initial_rewards_pool_balance) = chain_state();
+        assert_eq!(initial_rewards_pool_balance, 0); // ED is auto-deducted by the getter function
+
+        // Running chain until era rollover
+        run_to_block(era_duration + 1);
+
+        // No payout is expected for era #0 anyway because the "official" staked amount is 0
+        assert_eq!(
+            Staking::eras_validator_reward(0)
+                .expect("ErasValidatorReward storage must exist after era end; qed"),
+            0
+        );
+
+        // Running chain until the next era rollover
+        run_to_block(2 * era_duration + 1);
+
+        // Claim rewards to trigger rewards minting
+        for era in 0_u32..2 {
+            pallet_staking::Validators::<Test>::iter().for_each(|(stash_id, _)| {
+                assert_ok!(Staking::payout_stakers(
+                    RuntimeOrigin::signed(SIGNER),
+                    stash_id,
+                    era
+                ));
+            });
+        }
+
+        // Take up-to-date measurements of the chain stats
+        let (total_issuance, _, _, rewards_pool_balance) = chain_state();
+
+        // The rewards pool balance is still 0: we should have failed to offset any rewards
+        assert_eq!(initial_rewards_pool_balance, rewards_pool_balance);
+        // Staker rewards for eras 0 and 1
+        let actual_rewards = Staking::eras_validator_reward(1)
+            .expect("ErasValidatorReward storage must exist after era end; qed");
+        // Total issuance grew accordingly have changed
+        assert_eq!(total_issuance, initial_total_issuance + actual_rewards);
+    });
+}
+
 fn sensible_defaults() -> (Perquintill, Perquintill, u128, Perquintill) {
     (
         Perquintill::from_rational(578_u64, 10_000_u64),