fix: clean up AllowancesStorage on subnet deregistration

Add PrecompileCleanupInterface trait to allow the pallet to invoke
cross-crate storage cleanup when a subnet is removed. The precompiles
crate iterates and removes all AllowancesStorage entries matching the
dissolved netuid, preventing stale EVM approvals from carrying over
when the netuid is recycled.

Author: plind-junior

pallets/subtensor/src/coinbase/root.rs

@@ -218,6 +218,7 @@ impl<T: Config> Pallet<T> {
         Self::destroy_alpha_in_out_stakes(netuid)?;
         T::SwapInterface::clear_protocol_liquidity(netuid)?;
         T::CommitmentsInterface::purge_netuid(netuid);
+        T::PrecompileCleanupInterface::purge_netuid(netuid);
 
         // --- Remove the network
         Self::remove_network(netuid);

pallets/subtensor/src/lib.rs

@@ -2747,3 +2747,8 @@ impl<T> ProxyInterface<T> for () {
 pub trait CommitmentsInterface {
     fn purge_netuid(netuid: NetUid);
 }
+
+/// EVM precompile crates implement this to clean up storage when a subnet is removed.
+pub trait PrecompileCleanupInterface {
+    fn purge_netuid(netuid: NetUid);
+}

pallets/subtensor/src/macros/config.rs

@@ -6,7 +6,7 @@ use frame_support::pallet_macros::pallet_section;
 #[pallet_section]
 mod config {
 
-    use crate::{CommitmentsInterface, GetAlphaForTao, GetTaoForAlpha};
+    use crate::{CommitmentsInterface, GetAlphaForTao, GetTaoForAlpha, PrecompileCleanupInterface};
     use pallet_commitments::GetCommitments;
     use subtensor_runtime_common::AuthorshipInfo;
     use subtensor_swap_interface::{SwapEngine, SwapHandler};
@@ -60,6 +60,9 @@ mod config {
         ///  Interface to clean commitments on network dissolution.
         type CommitmentsInterface: CommitmentsInterface;
 
+        /// Interface to clean EVM precompile storage on network dissolution.
+        type PrecompileCleanupInterface: PrecompileCleanupInterface;
+
         /// Rate limit for associating an EVM key.
         type EvmKeyAssociateRateLimit: Get<u64>;
 

pallets/subtensor/src/tests/mock.rs

@@ -319,6 +319,7 @@ impl crate::Config for Test {
     type GetCommitments = ();
     type MaxImmuneUidsPercentage = MaxImmuneUidsPercentage;
     type CommitmentsInterface = CommitmentsI;
+    type PrecompileCleanupInterface = PrecompileCleanupI;
     type EvmKeyAssociateRateLimit = EvmKeyAssociateRateLimit;
     type AuthorshipProvider = MockAuthorshipProvider;
     type WeightInfo = ();
@@ -361,6 +362,11 @@ impl CommitmentsInterface for CommitmentsI {
     fn purge_netuid(_netuid: NetUid) {}
 }
 
+pub struct PrecompileCleanupI;
+impl PrecompileCleanupInterface for PrecompileCleanupI {
+    fn purge_netuid(_netuid: NetUid) {}
+}
+
 parameter_types! {
     pub MaximumSchedulerWeight: Weight = Perbill::from_percent(80) *
         BlockWeights::get().max_block;

precompiles/src/lib.rs

@@ -55,7 +55,7 @@ mod metagraph;
 mod neuron;
 mod proxy;
 mod sr25519;
-mod staking;
+pub mod staking;
 mod storage_query;
 mod subnet;
 mod uid_lookup;

precompiles/src/staking.rs

@@ -74,6 +74,22 @@ pub type AllowancesStorage = StorageDoubleMap<
     ValueQuery,
 >;
 
+/// Remove all AllowancesStorage entries whose key contains the given netuid.
+pub fn purge_netuid_allowances(netuid: u16) {
+    let to_remove: Vec<(H160, (H160, u16))> = AllowancesStorage::iter()
+        .filter_map(|(approver, (spender, n), _)| {
+            if n == netuid {
+                Some((approver, (spender, n)))
+            } else {
+                None
+            }
+        })
+        .collect();
+    for (approver, key) in to_remove {
+        AllowancesStorage::remove(approver, key);
+    }
+}
+
 // Old StakingPrecompile had ETH-precision in values, which was not alligned with Substrate API. So
 // it's kinda deprecated, but exists for backward compatibility. Eventually, we should remove it
 // to stop supporting both precompiles.
@@ -895,3 +911,32 @@ fn try_u64_from_u256(value: U256) -> Result<u64, PrecompileFailure> {
         exit_status: ExitError::Other("the value is outside of u64 bounds".into()),
     })
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn purge_netuid_allowances_removes_only_target_netuid() {
+        sp_io::TestExternalities::default().execute_with(|| {
+            let approver = H160::from_low_u64_be(1);
+            let spender = H160::from_low_u64_be(2);
+            let netuid_a: u16 = 5;
+            let netuid_b: u16 = 7;
+
+            AllowancesStorage::insert(approver, (spender, netuid_a), U256::from(100));
+            AllowancesStorage::insert(approver, (spender, netuid_b), U256::from(200));
+
+            purge_netuid_allowances(netuid_a);
+
+            assert_eq!(
+                AllowancesStorage::get(approver, (spender, netuid_a)),
+                U256::zero(),
+            );
+            assert_eq!(
+                AllowancesStorage::get(approver, (spender, netuid_b)),
+                U256::from(200),
+            );
+        });
+    }
+}

runtime/src/lib.rs

@@ -41,7 +41,7 @@ use pallet_subtensor::rpc_info::{
     stake_info::StakeInfo,
     subnet_info::{SubnetHyperparams, SubnetHyperparamsV2, SubnetInfo, SubnetInfov2},
 };
-use pallet_subtensor::{CommitmentsInterface, ProxyInterface};
+use pallet_subtensor::{CommitmentsInterface, PrecompileCleanupInterface, ProxyInterface};
 use pallet_subtensor_proxy as pallet_proxy;
 use pallet_subtensor_swap_runtime_api::{SimSwapResult, SubnetPrice};
 use pallet_subtensor_utility as pallet_utility;
@@ -878,6 +878,13 @@ impl CommitmentsInterface for CommitmentsI {
     }
 }
 
+pub struct PrecompileCleanupI;
+impl PrecompileCleanupInterface for PrecompileCleanupI {
+    fn purge_netuid(netuid: NetUid) {
+        subtensor_precompiles::staking::purge_netuid_allowances(<u16 as From<NetUid>>::from(netuid));
+    }
+}
+
 parameter_types! {
     pub MaximumSchedulerWeight: Weight = Perbill::from_percent(80) *
         BlockWeights::get().max_block;
@@ -1199,6 +1206,7 @@ impl pallet_subtensor::Config for Runtime {
     type GetCommitments = GetCommitmentsStruct;
     type MaxImmuneUidsPercentage = MaxImmuneUidsPercentage;
     type CommitmentsInterface = CommitmentsI;
+    type PrecompileCleanupInterface = PrecompileCleanupI;
     type EvmKeyAssociateRateLimit = EvmKeyAssociateRateLimit;
     type AuthorshipProvider = BlockAuthorFromAura<Aura>;
     type WeightInfo = pallet_subtensor::weights::SubstrateWeight<Runtime>;