refactor: remove ERC20 dependency from BaseInterchainToken

contracts/interchain-token/BaseInterchainToken.sol

@@ -5,14 +5,11 @@ pragma solidity ^0.8.0;
 import { IInterchainTokenStandard } from '../interfaces/IInterchainTokenStandard.sol';
 import { IInterchainTokenService } from '../interfaces/IInterchainTokenService.sol';
 
-import { ERC20 } from './ERC20.sol';
-
 /**
  * @title An example implementation of the IInterchainTokenStandard.
- * @notice The implementation ERC20 can be done in any way, however this example assumes that an _approve internal function exists
- * that can be used to create approvals, and that `allowance` is a mapping.
+ * @notice The is an abstract contract that needs to be extended with an ERC20 implementation. See `InterchainToken` for an example implementation.
  */
-abstract contract BaseInterchainToken is IInterchainTokenStandard, ERC20 {
+abstract contract BaseInterchainToken is IInterchainTokenStandard {
     /**
      * @notice Getter for the tokenId used for this token.
      * @dev Needs to be overwritten.
@@ -48,6 +45,7 @@ abstract contract BaseInterchainToken is IInterchainTokenStandard, ERC20 {
         _beforeInterchainTransfer(msg.sender, destinationChain, recipient, amount, metadata);
 
         IInterchainTokenService service = IInterchainTokenService(interchainTokenService());
+
         service.transmitInterchainTransfer{ value: msg.value }(interchainTokenId(), sender, destinationChain, recipient, amount, metadata);
     }
 
@@ -68,15 +66,12 @@ abstract contract BaseInterchainToken is IInterchainTokenStandard, ERC20 {
         uint256 amount,
         bytes calldata metadata
     ) external payable {
-        uint256 _allowance = allowance[sender][msg.sender];
-
-        if (_allowance != UINT256_MAX) {
-            _approve(sender, msg.sender, _allowance - amount);
-        }
+        _spendAllowance(sender, msg.sender, amount);
 
         _beforeInterchainTransfer(sender, destinationChain, recipient, amount, metadata);
 
         IInterchainTokenService service = IInterchainTokenService(interchainTokenService());
+
         service.transmitInterchainTransfer{ value: msg.value }(interchainTokenId(), sender, destinationChain, recipient, amount, metadata);
     }
 
@@ -96,4 +91,10 @@ abstract contract BaseInterchainToken is IInterchainTokenStandard, ERC20 {
         uint256 amount,
         bytes calldata metadata
     ) internal virtual {}
+
+    /**
+     * @notice A method to be overwritten that will decrease the allowance of the `spender` from `sender` by `amount`.
+     * @dev Needs to be overwritten. This provides flexibility for the choice of ERC20 implementation used. Must revert if allowance is not sufficient.
+     */
+    function _spendAllowance(address sender, address spender, uint256 amount) internal virtual;
 }

contracts/interchain-token/InterchainToken.sol

@@ -7,6 +7,7 @@ import { AddressBytes } from '@axelar-network/axelar-gmp-sdk-solidity/contracts/
 import { IInterchainToken } from '../interfaces/IInterchainToken.sol';
 
 import { BaseInterchainToken } from './BaseInterchainToken.sol';
+import { ERC20 } from './ERC20.sol';
 import { ERC20Permit } from './ERC20Permit.sol';
 import { Minter } from '../utils/Minter.sol';
 
@@ -15,7 +16,7 @@ import { Minter } from '../utils/Minter.sol';
  * @notice This contract implements an interchain token which extends InterchainToken functionality.
  * @dev This contract also inherits Minter and Implementation logic.
  */
-contract InterchainToken is BaseInterchainToken, ERC20Permit, Minter, IInterchainToken {
+contract InterchainToken is BaseInterchainToken, ERC20, ERC20Permit, Minter, IInterchainToken {
     using AddressBytes for bytes;
 
     string public name;
@@ -125,4 +126,16 @@ contract InterchainToken is BaseInterchainToken, ERC20Permit, Minter, IInterchai
     function burn(address account, uint256 amount) external onlyRole(uint8(Roles.MINTER)) {
         _burn(account, amount);
     }
+
+    /**
+     * @notice A method to be overwritten that will decrease the allowance of the `spender` from `sender` by `amount`.
+     * @dev Needs to be overwritten. This provides flexibility for the choice of ERC20 implementation used. Must revert if allowance is not sufficient.
+     */
+    function _spendAllowance(address sender, address spender, uint256 amount) internal override {
+        uint256 _allowance = allowance[sender][spender];
+
+        if (_allowance != UINT256_MAX) {
+            _approve(sender, spender, _allowance - amount);
+        }
+    }
 }

contracts/test/TestBaseInterchainToken.sol

@@ -3,10 +3,11 @@
 pragma solidity ^0.8.0;
 
 import { BaseInterchainToken } from '../interchain-token/BaseInterchainToken.sol';
+import { ERC20 } from '../interchain-token/ERC20.sol';
 import { Minter } from '../utils/Minter.sol';
 import { IERC20MintableBurnable } from '../interfaces/IERC20MintableBurnable.sol';
 
-contract TestBaseInterchainToken is BaseInterchainToken, Minter, IERC20MintableBurnable {
+contract TestBaseInterchainToken is BaseInterchainToken, Minter, ERC20, IERC20MintableBurnable {
     address internal service;
     bytes32 internal tokenId;
     bool internal tokenManagerRequiresApproval_ = true;
@@ -52,6 +53,14 @@ contract TestBaseInterchainToken is BaseInterchainToken, Minter, IERC20MintableB
         }
     }
 
+    function _spendAllowance(address sender, address spender, uint256 amount) internal override {
+        uint256 _allowance = allowance[sender][spender];
+
+        if (_allowance != UINT256_MAX) {
+            _approve(sender, spender, _allowance - amount);
+        }
+    }
+
     function setTokenManagerRequiresApproval(bool requiresApproval) public {
         tokenManagerRequiresApproval_ = requiresApproval;
     }

contracts/test/TestFeeOnTransferToken.sol

@@ -3,10 +3,11 @@
 pragma solidity ^0.8.0;
 
 import { BaseInterchainToken } from '../interchain-token/BaseInterchainToken.sol';
+import { ERC20 } from '../interchain-token/ERC20.sol';
 import { Minter } from '../utils/Minter.sol';
 import { IERC20MintableBurnable } from '../interfaces/IERC20MintableBurnable.sol';
 
-contract TestFeeOnTransferToken is BaseInterchainToken, Minter, IERC20MintableBurnable {
+contract TestFeeOnTransferToken is BaseInterchainToken, ERC20, Minter, IERC20MintableBurnable {
     address public immutable service;
     bytes32 public tokenId;
     bool internal tokenManagerRequiresApproval_ = true;
@@ -51,6 +52,14 @@ contract TestFeeOnTransferToken is BaseInterchainToken, Minter, IERC20MintableBu
         }
     }
 
+    function _spendAllowance(address sender, address spender, uint256 amount) internal override {
+        uint256 _allowance = allowance[sender][spender];
+
+        if (_allowance != UINT256_MAX) {
+            _approve(sender, spender, _allowance - amount);
+        }
+    }
+
     function setTokenManagerRequiresApproval(bool requiresApproval) public {
         tokenManagerRequiresApproval_ = requiresApproval;
     }