fix: Migrate transformers to smart contract compatible unsafeTransformerTransfer [TKR-587] (#594)

* Use `call` instead of `transfer` in `LibERC20Transformer`

* Since `transfer` only forwards 2300 gas it can cause an `out of gas`
revert when the receipient is a smart contract.

* Add `unsafeTransformerTransfer` and migrate `transformers` to use
`unsafeTransformerTransfer` instead of `transformerTransfer`

* Update .prettierignore

contracts/zero-ex/contracts/src/transformers/AffiliateFeeTransformer.sol

@@ -61,7 +61,7 @@ contract AffiliateFeeTransformer is Transformer {
                 amount = LibERC20Transformer.getTokenBalanceOf(fees[i].token, address(this));
             }
             if (amount != 0) {
-                fees[i].token.transformerTransfer(fees[i].recipient, amount);
+                fees[i].token.unsafeTransformerTransfer(fees[i].recipient, amount);
             }
         }
 

contracts/zero-ex/contracts/src/transformers/LibERC20Transformer.sol

@@ -34,7 +34,9 @@ library LibERC20Transformer {
     ///      This is just `keccak256('TRANSFORMER_SUCCESS')`.
     bytes4 internal constant TRANSFORMER_SUCCESS = 0x13c9929e;
 
-    /// @dev Transfer ERC20 tokens and ETH.
+    /// @dev Transfer ERC20 tokens and ETH. Since it relies on `transfer` it may run out of gas when
+    /// the `recipient` is a smart contract wallet. See `unsafeTransformerTransfer` for smart contract
+    /// compatible transfer.
     /// @param token An ERC20 or the ETH pseudo-token address (`ETH_TOKEN_ADDRESS`).
     /// @param to The recipient.
     /// @param amount The transfer amount.
@@ -50,6 +52,24 @@ library LibERC20Transformer {
         }
     }
 
+    /// @dev Transfer ERC20 tokens and ETH. For ETH transfer. It's not safe from re-entrancy attacks and the
+    /// caller is responsible for gurading against a potential re-entrancy attack.
+    /// @param token An ERC20 or the ETH pseudo-token address (`ETH_TOKEN_ADDRESS`).
+    /// @param to The recipient.
+    /// @param amount The transfer amount.
+    function unsafeTransformerTransfer(
+        IERC20TokenV06 token,
+        address payable to,
+        uint256 amount
+    ) internal {
+        if (isTokenETH(token)) {
+            (bool sent, ) = to.call{value: amount}("");
+            require(sent, "LibERC20Transformer/FAILED_TO_SEND_ETHER");
+        } else {
+            token.compatTransfer(to, amount);
+        }
+    }
+
     /// @dev Check if a token is the ETH pseudo-token.
     /// @param token The token to check.
     /// @return isETH `true` if the token is the ETH pseudo-token.

contracts/zero-ex/contracts/src/transformers/PayTakerTransformer.sol

@@ -65,7 +65,7 @@ contract PayTakerTransformer is Transformer {
                 amount = data.tokens[i].getTokenBalanceOf(address(this));
             }
             if (amount != 0) {
-                data.tokens[i].transformerTransfer(context.recipient, amount);
+                data.tokens[i].unsafeTransformerTransfer(context.recipient, amount);
             }
         }
         return LibERC20Transformer.TRANSFORMER_SUCCESS;

contracts/zero-ex/contracts/src/transformers/PositiveSlippageFeeTransformer.sol

@@ -53,7 +53,7 @@ contract PositiveSlippageFeeTransformer is Transformer {
         uint256 transformerAmount = LibERC20Transformer.getTokenBalanceOf(fee.token, address(this));
         if (transformerAmount > fee.bestCaseAmount) {
             uint256 positiveSlippageAmount = transformerAmount - fee.bestCaseAmount;
-            fee.token.transformerTransfer(fee.recipient, positiveSlippageAmount);
+            fee.token.unsafeTransformerTransfer(fee.recipient, positiveSlippageAmount);
         }
 
         return LibERC20Transformer.TRANSFORMER_SUCCESS;