Swap Stake Between Subnets

pallets/subtensor/src/macros/dispatches.rs

@@ -1608,9 +1608,6 @@ mod dispatches {
         /// * `destination_netuid` - The network/subnet ID to move stake to (for cross-subnet transfer).
         /// * `alpha_amount` - The amount of stake to transfer.
         ///
-        /// # Weight
-        /// Uses a fixed weight of 3_000_000 (plus any DB write overhead).
-        ///
         /// # Errors
         /// Returns an error if:
         /// * The origin is not signed by the correct coldkey.
@@ -1640,5 +1637,46 @@ mod dispatches {
                 alpha_amount,
             )
         }
+
+        /// Swaps a specified amount of stake from one subnet to another, while keeping the same coldkey and hotkey.
+        ///
+        /// # Arguments
+        /// * `origin` - The origin of the transaction, which must be signed by the coldkey that owns the `hotkey`.
+        /// * `hotkey` - The hotkey whose stake is being swapped.
+        /// * `origin_netuid` - The network/subnet ID from which stake is removed.
+        /// * `destination_netuid` - The network/subnet ID to which stake is added.
+        /// * `alpha_amount` - The amount of stake to swap.
+        ///
+        /// # Errors
+        /// Returns an error if:
+        /// * The transaction is not signed by the correct coldkey (i.e., `coldkey_owns_hotkey` fails).
+        /// * Either `origin_netuid` or `destination_netuid` does not exist.
+        /// * The hotkey does not exist.
+        /// * There is insufficient stake on `(coldkey, hotkey, origin_netuid)`.
+        /// * The swap amount is below the minimum stake requirement.
+        ///
+        /// # Events
+        /// May emit a `StakeSwapped` event on success.
+        #[pallet::call_index(87)]
+        #[pallet::weight((
+            Weight::from_parts(3_000_000, 0).saturating_add(T::DbWeight::get().writes(1)),
+            DispatchClass::Operational,
+            Pays::No
+        ))]
+        pub fn swap_stake(
+            origin: T::RuntimeOrigin,
+            hotkey: T::AccountId,
+            origin_netuid: u16,
+            destination_netuid: u16,
+            alpha_amount: u64,
+        ) -> DispatchResult {
+            Self::do_swap_stake(
+                origin,
+                hotkey,
+                origin_netuid,
+                destination_netuid,
+                alpha_amount,
+            )
+        }
     }
 }

pallets/subtensor/src/macros/events.rs

@@ -253,5 +253,11 @@ mod events {
         /// Parameters:
         /// (origin_coldkey, destination_coldkey, hotkey, origin_netuid, destination_netuid, amount)
         StakeTransferred(T::AccountId, T::AccountId, T::AccountId, u16, u16, u64),
+
+        /// Stake has been swapped from one subnet to another for the same coldkey-hotkey pair.
+        ///
+        /// Parameters:
+        /// (coldkey, hotkey, origin_netuid, destination_netuid, amount)
+        StakeSwapped(T::AccountId, T::AccountId, u16, u16, u64),
     }
 }

pallets/subtensor/src/staking/move_stake.rs

@@ -217,4 +217,101 @@ impl<T: Config> Pallet<T> {
         // 10. Return success.
         Ok(())
     }
+
+    /// Swaps a specified amount of stake for the same `(coldkey, hotkey)` pair from one subnet
+    /// (`origin_netuid`) to another (`destination_netuid`).
+    ///
+    /// # Arguments
+    /// * `origin` - The origin of the transaction, which must be signed by the coldkey that owns the hotkey.
+    /// * `hotkey` - The hotkey whose stake is being swapped.
+    /// * `origin_netuid` - The subnet ID from which stake is removed.
+    /// * `destination_netuid` - The subnet ID to which stake is added.
+    /// * `alpha_amount` - The amount of stake to swap.
+    ///
+    /// # Returns
+    /// * `DispatchResult` - Indicates success or failure.
+    ///
+    /// # Errors
+    /// This function returns an error if:
+    /// * The origin is not signed by the correct coldkey (i.e., not associated with `hotkey`).
+    /// * Either the `origin_netuid` or the `destination_netuid` does not exist.
+    /// * The specified `hotkey` does not exist.
+    /// * The `(coldkey, hotkey, origin_netuid)` does not have enough stake (`alpha_amount`).
+    /// * The unstaked amount is below `DefaultMinStake`.
+    ///
+    /// # Events
+    /// Emits a `StakeSwapped` event upon successful completion.
+    pub fn do_swap_stake(
+        origin: T::RuntimeOrigin,
+        hotkey: T::AccountId,
+        origin_netuid: u16,
+        destination_netuid: u16,
+        alpha_amount: u64,
+    ) -> dispatch::DispatchResult {
+        // 1. Ensure the extrinsic is signed by the coldkey.
+        let coldkey = ensure_signed(origin)?;
+
+        // 2. Check that both subnets exist.
+        ensure!(
+            Self::if_subnet_exist(origin_netuid),
+            Error::<T>::SubnetNotExists
+        );
+        ensure!(
+            Self::if_subnet_exist(destination_netuid),
+            Error::<T>::SubnetNotExists
+        );
+
+        // 3. Check that the hotkey exists.
+        ensure!(
+            Self::hotkey_account_exists(&hotkey),
+            Error::<T>::HotKeyAccountNotExists
+        );
+
+        // 4. Ensure this coldkey actually owns the hotkey.
+        ensure!(
+            Self::coldkey_owns_hotkey(&coldkey, &hotkey),
+            Error::<T>::NonAssociatedColdKey
+        );
+
+        // 5. Ensure there is enough stake in the origin subnet.
+        let origin_alpha =
+            Self::get_stake_for_hotkey_and_coldkey_on_subnet(&hotkey, &coldkey, origin_netuid);
+        ensure!(
+            alpha_amount <= origin_alpha,
+            Error::<T>::NotEnoughStakeToWithdraw
+        );
+
+        // 6. Unstake from the origin subnet, returning TAO (or a 1:1 equivalent).
+        let tao_unstaked =
+            Self::unstake_from_subnet(&hotkey, &coldkey, origin_netuid, alpha_amount);
+
+        // 7. Check that the unstaked amount is above the minimum stake threshold.
+        ensure!(
+            tao_unstaked >= DefaultMinStake::<T>::get(),
+            Error::<T>::AmountTooLow
+        );
+
+        // 8. Stake the unstaked amount into the destination subnet, using the same coldkey/hotkey.
+        Self::stake_into_subnet(&hotkey, &coldkey, destination_netuid, tao_unstaked);
+
+        // 9. Emit an event for logging.
+        log::info!(
+            "StakeSwapped(coldkey: {:?}, hotkey: {:?}, origin_netuid: {:?}, destination_netuid: {:?}, amount: {:?})",
+            coldkey,
+            hotkey,
+            origin_netuid,
+            destination_netuid,
+            tao_unstaked
+        );
+        Self::deposit_event(Event::StakeSwapped(
+            coldkey,
+            hotkey,
+            origin_netuid,
+            destination_netuid,
+            tao_unstaked,
+        ));
+
+        // 10. Return success.
+        Ok(())
+    }
 }