Fix a hint handler bug, where it doesn't allow empty hint for one side of T2T hint

* Add a new hint type: best-of-all which is actually like an empty hint.

* New type enables one side in token to token trade to have an empty hint.

* best-of-all hint type actually triggers the "default" Kyber algorithm which chooses the reserve with the best rate for the taker

Author: ayobuenavista

Diff for: contracts/sol6/IKyberHint.sol

@@ -4,9 +4,10 @@ import "./IKyberReserve.sol";
 
 
 interface IKyberHint {
-    enum TradeType {MaskIn, MaskOut, Split}
+    enum TradeType {BestOfAll, MaskIn, MaskOut, Split}
     enum HintErrors {
         NoError, // Hint is valid
+        NonEmptyDataError, // reserveIDs and splits must be empty for BestOfAll hint
         ReserveIdDupError, // duplicate reserveID found
         ReserveIdEmptyError, // reserveIDs array is empty for MaskIn and Split trade type
         ReserveIdSplitsError, // reserveIDs and splitBpsValues arrays do not have the same length

Diff for: contracts/sol6/KyberHintHandler.sol

@@ -406,6 +406,10 @@ abstract contract KyberHintHandler is IKyberHint, Utils5 {
         bytes32[] memory reserveIds,
         uint256[] memory splits
     ) internal pure returns (HintErrors) {
+        if (tradeType == TradeType.BestOfAll) {
+            if (reserveIds.length != 0 || splits.length != 0) return HintErrors.NonEmptyDataError;
+        }
+
         if (
             (tradeType == TradeType.MaskIn || tradeType == TradeType.Split) &&
             reserveIds.length == 0
@@ -430,6 +434,7 @@ abstract contract KyberHintHandler is IKyberHint, Utils5 {
     /// @notice Throws error message to user to indicate error on hint
     /// @param error Error type from HintErrors enum
     function throwHintError(HintErrors error) internal pure {
+        if (error == HintErrors.NonEmptyDataError) revert("reserveIds and splits must be empty");
         if (error == HintErrors.ReserveIdDupError) revert("duplicate reserveId");
         if (error == HintErrors.ReserveIdEmptyError) revert("reserveIds cannot be empty");
         if (error == HintErrors.ReserveIdSplitsError) revert("reserveIds.length != splits.length");

Diff for: contracts/sol6/KyberMatchingEngine.sol

@@ -109,13 +109,16 @@ contract KyberMatchingEngine is KyberHintHandler, IKyberMatchingEngine, Withdraw
 
         if (tradeType == TradeType.MaskIn) {
             splitValuesBps = populateSplitValuesBps(reserveIds.length);
-        } else if (tradeType == TradeType.MaskOut) {
-            // if mask out, apply masking out logic
+        } else if (tradeType == TradeType.BestOfAll || tradeType == TradeType.MaskOut) {
             bytes32[] memory allReserves = (dest == ETH_TOKEN_ADDRESS)
                 ? kyberStorage.getReserveIdsPerTokenSrc(src)
                 : kyberStorage.getReserveIdsPerTokenDest(dest);
 
-            reserveIds = maskOutReserves(allReserves, reserveIds);
+            // if bestOfAll, reserveIds = allReserves
+            // if mask out, apply masking out logic
+            reserveIds = (tradeType == TradeType.BestOfAll) ?
+                allReserves :
+                maskOutReserves(allReserves, reserveIds);
             splitValuesBps = populateSplitValuesBps(reserveIds.length);
         }