SafeERC20: Add safe total supply (#543)

contracts/common/SafeERC20.sol

@@ -153,4 +153,17 @@ library SafeERC20 {
 
         return allowance;
     }
+
+    /**
+    * @dev Static call into ERC20.totalSupply().
+    * Reverts if the call fails for some reason (should never fail).
+    */
+    function staticTotalSupply(ERC20 _token) internal view returns (uint256) {
+        bytes memory totalSupplyCallData = abi.encodeWithSelector(_token.totalSupply.selector);
+
+        (bool success, uint256 totalSupply) = staticInvoke(_token, totalSupplyCallData);
+        require(success, ERROR_TOKEN_ALLOWANCE_REVERTED);
+
+        return totalSupply;
+    }
 }

contracts/test/mocks/lib/token/SafeERC20Mock.sol

@@ -33,4 +33,8 @@ contract SafeERC20Mock {
     function balanceOf(ERC20 token, address owner) external view returns (uint256) {
         return token.staticBalanceOf(owner);
     }
+
+    function totalSupply(ERC20 token) external view returns (uint256) {
+        return token.staticTotalSupply();
+    }
 }

test/contracts/common/safe_erc20.js

@@ -120,6 +120,12 @@ contract('SafeERC20', ([owner, receiver]) => {
         assert.equal(balance, initialBalance, 'Mock should return correct balance')
         assert.equal((await tokenMock.balanceOf(owner)).valueOf(), balance, "Mock should match token contract's balance")
       })
+
+      it('gives correct value with static totalSupply', async () => {
+        const totalSupply = (await safeERC20Mock.totalSupply(tokenMock.address)).valueOf()
+        assert.equal(totalSupply, initialBalance, 'Mock should return correct total supply')
+        assert.equal((await tokenMock.totalSupply()).valueOf(), totalSupply, "Mock should match token contract's total supply")
+      })
     })
   }
 })