ERC20: enable a subnet's supply to be determined by an ERC20 token in…

… the parent.

This commit introduces the concept of the "supply strategy". This configuration
object determines the kind of supply backing a subnet. It can be "native" or "ERC20".
In the latter case, the token address must be provided. We verify that the address
indeed corresponds to an ERC20 token.

This commit also adds a funcWithToken() external non-payable function to the GatewayManagerFacet.
This is analogous to fund(), but for token supply (where the amount must be passed as a parameter).

fund() and fundWithToken() validate that the expected supply kind is being used.

src/SubnetActorDiamond.sol

@@ -7,11 +7,12 @@ import {IDiamond} from "./interfaces/IDiamond.sol";
 import {IDiamondCut} from "./interfaces/IDiamondCut.sol";
 import {IDiamondLoupe} from "./interfaces/IDiamondLoupe.sol";
 import {IERC165} from "./interfaces/IERC165.sol";
-import {GatewayCannotBeZero, NotGateway, InvalidSubmissionPeriod, InvalidCollateral, InvalidMajorityPercentage, InvalidPowerScale} from "./errors/IPCErrors.sol";
+import {GatewayCannotBeZero, NotGateway, InvalidSubmissionPeriod, InvalidCollateral, InvalidMajorityPercentage, InvalidPowerScale, InvalidERC20Address} from "./errors/IPCErrors.sol";
 import {LibDiamond} from "./lib/LibDiamond.sol";
-import {SubnetID} from "./structs/Subnet.sol";
+import {SubnetID, SupplyKind, SupplyStrategy} from "./structs/Subnet.sol";
 import {SubnetIDHelper} from "./lib/SubnetIDHelper.sol";
 import {LibStaking} from "./lib/LibStaking.sol";
+import {IERC20} from "openzeppelin-contracts/token/ERC20/IERC20.sol";
 
 error FunctionNotFound(bytes4 _functionSelector);
 
@@ -32,6 +33,7 @@ contract SubnetActorDiamond {
         uint256 minCrossMsgFee;
         int8 powerScale;
         bool permissioned;
+        SupplyStrategy supplyStrategy;
     }
 
     constructor(IDiamond.FacetCut[] memory _diamondCut, ConstructorParams memory params) {
@@ -51,6 +53,16 @@ contract SubnetActorDiamond {
         if (params.powerScale > 18) {
             revert InvalidPowerScale();
         }
+        if (params.supplyStrategy.kind == SupplyKind.ERC20) {
+            if (params.supplyStrategy.tokenAddress == address(0)) {
+                revert InvalidERC20Address();
+            }
+            // We require that the ERC20 token exists beforehand.
+            // The call to balanceOf will revert if the supplied address does not exist, or if it's not an ERC20 contract.
+            // Ideally we'd be able to use ERC165 to check if the contract implements the ERC20 standard, but the latter does not support supportsInterface().
+            IERC20 token = IERC20(params.supplyStrategy.tokenAddress);
+            token.balanceOf(address(this));
+        }
 
         LibDiamond.setContractOwner(msg.sender);
         LibDiamond.diamondCut({_diamondCut: _diamondCut, _init: address(0), _calldata: new bytes(0)});
@@ -79,6 +91,8 @@ contract SubnetActorDiamond {
         // The startConfiguration number is also 1 to match with nextConfigurationNumber, indicating we have
         // empty validator change logs
         s.changeSet.startConfigurationNumber = LibStaking.INITIAL_CONFIGURATION_NUMBER;
+        // Set the supply strategy.
+        s.supplyStrategy = params.supplyStrategy;
     }
 
     function _fallback() internal {

src/errors/IPCErrors.sol

@@ -26,6 +26,7 @@ error InvalidCrossMsgDstSubnet();
 error InvalidCrossMsgFromSubnet();
 error InvalidCrossMsgNonce();
 error InvalidCrossMsgValue();
+error InvalidERC20Address();
 error InvalidMajorityPercentage();
 error InvalidPowerScale();
 error InvalidRetentionHeight();
@@ -61,12 +62,13 @@ error PQEmpty();
 error ParentFinalityAlreadyCommitted();
 error PostboxNotExist();
 error SignatureReplay();
+error SubnetAlreadyBootstrapped();
 error SubnetAlreadyKilled();
 error SubnetNotActive();
 error SubnetNotFound();
+error UnexpectedSupplyStrategy();
 error WithdrawExceedingCollateral();
 error ZeroMembershipWeight();
-error SubnetAlreadyBootstrapped();
 error FacetCannotBeZero();
 error WrongGateway();
 error CannotFindSubnet();

src/gateway/GatewayManagerFacet.sol

@@ -2,22 +2,27 @@
 pragma solidity 0.8.19;
 
 import {GatewayActorModifiers} from "../lib/LibGatewayActorStorage.sol";
+import {SubnetActorGetterFacet} from "../subnet/SubnetActorGetterFacet.sol";
 import {BURNT_FUNDS_ACTOR} from "../constants/Constants.sol";
 import {CrossMsg} from "../structs/Checkpoint.sol";
 import {Status} from "../enums/Status.sol";
 import {FvmAddress} from "../structs/FvmAddress.sol";
-import {SubnetID, Subnet} from "../structs/Subnet.sol";
-import {Membership} from "../structs/Subnet.sol";
-import {AlreadyRegisteredSubnet, CannotReleaseZero, NotEnoughFunds, NotEnoughFundsToRelease, NotEnoughCollateral, NotEmptySubnetCircSupply, NotRegisteredSubnet, InvalidCrossMsgValue} from "../errors/IPCErrors.sol";
+import {SubnetID, Subnet, SupplyStrategy} from "../structs/Subnet.sol";
+import {Membership, SupplyKind} from "../structs/Subnet.sol";
+import {AlreadyRegisteredSubnet, CannotReleaseZero, NotEnoughFunds, NotEnoughFundsToRelease, NotEnoughCollateral, NotEmptySubnetCircSupply, NotRegisteredSubnet, InvalidCrossMsgValue, UnexpectedSupplyStrategy} from "../errors/IPCErrors.sol";
 import {LibGateway} from "../lib/LibGateway.sol";
 import {SubnetIDHelper} from "../lib/SubnetIDHelper.sol";
 import {CrossMsgHelper} from "../lib/CrossMsgHelper.sol";
 import {FilAddress} from "fevmate/utils/FilAddress.sol";
 import {ReentrancyGuard} from "../lib/LibReentrancyGuard.sol";
+import {IERC20} from "openzeppelin-contracts/token/ERC20/IERC20.sol";
+import {SafeERC20} from "openzeppelin-contracts/token/ERC20/utils/SafeERC20.sol";
+import {Address} from "openzeppelin-contracts/utils/Address.sol";
 
 contract GatewayManagerFacet is GatewayActorModifiers, ReentrancyGuard {
     using FilAddress for address payable;
     using SubnetIDHelper for SubnetID;
+    using SafeERC20 for IERC20;
 
     /// @notice register a subnet in the gateway. It is called by a subnet when it reaches the threshold stake
     /// @dev The subnet can optionally pass a genesis circulating supply that would be pre-allocated in the
@@ -142,6 +147,12 @@ contract GatewayManagerFacet is GatewayActorModifiers, ReentrancyGuard {
             // prevent spamming if there's no value to fund.
             revert InvalidCrossMsgValue();
         }
+        // Validate that the supply strategy is native.
+        SupplyStrategy memory supplyStrategy = SubnetActorGetterFacet(subnetId.getActor()).supplyStrategy();
+        if (supplyStrategy.kind != SupplyKind.Native) {
+            revert UnexpectedSupplyStrategy();
+        }
+
         CrossMsg memory crossMsg = CrossMsgHelper.createFundMsg({
             subnet: subnetId,
             signer: msg.sender,
@@ -154,6 +165,31 @@ contract GatewayManagerFacet is GatewayActorModifiers, ReentrancyGuard {
         LibGateway.commitTopDownMsg(crossMsg);
     }
 
+    function fundWithToken(SubnetID calldata subnetId, FvmAddress calldata to, uint256 amount) external nonReentrant {
+        // Check that the supply strategy is ERC20.
+        // There is no need to check whether the subnet exists. If it doesn't exist, the call to getter will revert.
+        // LibGateway.commitTopDownMsg will also revert if the subnet doesn't exist.
+        SupplyStrategy memory supplyStrategy = SubnetActorGetterFacet(subnetId.getActor()).supplyStrategy();
+        if (supplyStrategy.kind != SupplyKind.ERC20) {
+            revert UnexpectedSupplyStrategy();
+        }
+
+        // Transfer the specified token amount to the gateway to lock it.
+        IERC20(supplyStrategy.tokenAddress).safeTransferFrom({from: msg.sender, to: address(this), value: amount});
+
+        // Create the top-down message to mint the supply in the subnet.
+        CrossMsg memory crossMsg = CrossMsgHelper.createFundMsg({
+            subnet: subnetId,
+            signer: msg.sender,
+            to: to,
+            value: amount,
+            fee: 0 // injecting funds into a subnet should is free
+        });
+
+        // Commit top-down message.
+        LibGateway.commitTopDownMsg(crossMsg);
+    }
+
     /// @notice release() burns the received value and releases them from this subnet onto the parent by committing a bottom-up message.
     ///
     /// @param to: the address to which to credit funds in the parent subnet.

src/lib/LibSubnetActorStorage.sol

@@ -5,7 +5,7 @@ import {ConsensusType} from "../enums/ConsensusType.sol";
 import {NotGateway, SubnetAlreadyKilled} from "../errors/IPCErrors.sol";
 import {FvmAddress} from "../structs/FvmAddress.sol";
 import {BottomUpCheckpoint} from "../structs/Checkpoint.sol";
-import {SubnetID, ValidatorSet, StakingChangeLog, StakingReleaseQueue, Validator} from "../structs/Subnet.sol";
+import {SubnetID, ValidatorSet, StakingChangeLog, StakingReleaseQueue, SupplyStrategy, Validator} from "../structs/Subnet.sol";
 import {Address} from "openzeppelin-contracts/utils/Address.sol";
 import {EnumerableSet} from "openzeppelin-contracts/utils/structs/EnumerableSet.sol";
 
@@ -67,6 +67,8 @@ struct SubnetActorStorage {
     mapping(address => string) bootstrapNodes;
     /// @notice the list ov validators that announces bootstrap nodes
     EnumerableSet.AddressSet bootstrapOwners;
+    /// @notice subnet supply strategy.
+    SupplyStrategy supplyStrategy;
 }
 
 library LibSubnetActorStorage {

src/structs/Subnet.sol

@@ -138,3 +138,14 @@ struct Membership {
     Validator[] validators;
     uint64 configurationNumber;
 }
+
+struct SupplyStrategy {
+    SupplyKind kind;
+    address tokenAddress;
+}
+
+/// @title Determines the type of supply used by the subnet.
+enum SupplyKind {
+    Native,
+    ERC20
+}

src/subnet/SubnetActorGetterFacet.sol

@@ -3,7 +3,7 @@ pragma solidity 0.8.19;
 
 import {ConsensusType} from "../enums/ConsensusType.sol";
 import {BottomUpCheckpoint, CrossMsg} from "../structs/Checkpoint.sol";
-import {SubnetID} from "../structs/Subnet.sol";
+import {SubnetID, SupplyStrategy} from "../structs/Subnet.sol";
 import {SubnetID, ValidatorInfo, Validator} from "../structs/Subnet.sol";
 import {SubnetActorStorage} from "../lib/LibSubnetActorStorage.sol";
 import {SubnetIDHelper} from "../lib/SubnetIDHelper.sol";
@@ -189,4 +189,9 @@ contract SubnetActorGetterFacet {
     function getRelayerReward(address relayer) external view returns (uint256) {
         return s.relayerRewards[relayer];
     }
+
+    /// @notice Returns the supply strategy for the subnet.
+    function supplyStrategy() external view returns (SupplyStrategy memory supply) {
+        return s.supplyStrategy;
+    }
 }