Sip 185 debt shares

contracts/BaseSynthetix.sol

@@ -9,7 +9,6 @@ import "./interfaces/ISynthetix.sol";
 // Internal references
 import "./interfaces/ISynth.sol";
 import "./TokenState.sol";
-import "./interfaces/ISynthetixState.sol";
 import "./interfaces/ISystemStatus.sol";
 import "./interfaces/IExchanger.sol";
 import "./interfaces/IIssuer.sol";
@@ -26,7 +25,6 @@ contract BaseSynthetix is IERC20, ExternStateToken, MixinResolver, ISynthetix {
     bytes32 public constant sUSD = "sUSD";
 
     // ========== ADDRESS RESOLVER CONFIGURATION ==========
-    bytes32 private constant CONTRACT_SYNTHETIXSTATE = "SynthetixState";
     bytes32 private constant CONTRACT_SYSTEMSTATUS = "SystemStatus";
     bytes32 private constant CONTRACT_EXCHANGER = "Exchanger";
     bytes32 private constant CONTRACT_ISSUER = "Issuer";
@@ -50,16 +48,11 @@ contract BaseSynthetix is IERC20, ExternStateToken, MixinResolver, ISynthetix {
 
     // Note: use public visibility so that it can be invoked in a subclass
     function resolverAddressesRequired() public view returns (bytes32[] memory addresses) {
-        addresses = new bytes32[](5);
-        addresses[0] = CONTRACT_SYNTHETIXSTATE;
-        addresses[1] = CONTRACT_SYSTEMSTATUS;
-        addresses[2] = CONTRACT_EXCHANGER;
-        addresses[3] = CONTRACT_ISSUER;
-        addresses[4] = CONTRACT_REWARDSDISTRIBUTION;
-    }
-
-    function synthetixState() internal view returns (ISynthetixState) {
-        return ISynthetixState(requireAndGetAddress(CONTRACT_SYNTHETIXSTATE));
+        addresses = new bytes32[](4);
+        addresses[0] = CONTRACT_SYSTEMSTATUS;
+        addresses[1] = CONTRACT_EXCHANGER;
+        addresses[2] = CONTRACT_ISSUER;
+        addresses[3] = CONTRACT_REWARDSDISTRIBUTION;
     }
 
     function systemStatus() internal view returns (ISystemStatus) {
@@ -147,14 +140,13 @@ contract BaseSynthetix is IERC20, ExternStateToken, MixinResolver, ISynthetix {
     }
 
     function _canTransfer(address account, uint value) internal view returns (bool) {
-        (uint initialDebtOwnership, ) = synthetixState().issuanceData(account);
-
-        if (initialDebtOwnership > 0) {
+        if (issuer().debtBalanceOf(account, "sUSD") > 0) {
             (uint transferable, bool anyRateIsInvalid) =
                 issuer().transferableSynthetixAndAnyRateIsInvalid(account, tokenState.balanceOf(account));
             require(value <= transferable, "Cannot transfer staked or escrowed SNX");
             require(!anyRateIsInvalid, "A synth or SNX rate is invalid");
         }
+
         return true;
     }