Use high resolution credits on new contract accounts. (#603)

Increasing resolution on new, non-rebasing contracts.

Author: DanielVF

contracts/contracts/token/OUSD.sol

@@ -382,12 +382,22 @@ contract OUSD is Initializable, InitializableERC20Detailed, Governable {
      */
     function _ensureRebasingMigration(address _account) internal {
         if (nonRebasingCreditsPerToken[_account] == 0) {
-            // Set fixed credits per token for this account
-            nonRebasingCreditsPerToken[_account] = rebasingCreditsPerToken;
-            // Update non rebasing supply
-            nonRebasingSupply = nonRebasingSupply.add(balanceOf(_account));
-            // Update credit tallies
-            rebasingCredits = rebasingCredits.sub(_creditBalances[_account]);
+            if (_creditBalances[_account] == 0) {
+                // Since there is no existing balance, we can directly set to
+                // high resolution, and do not have to do any other bookkeeping
+                nonRebasingCreditsPerToken[_account] = 1e27;
+            } else {
+                // Migrate an existing account:
+
+                // Set fixed credits per token for this account
+                nonRebasingCreditsPerToken[_account] = rebasingCreditsPerToken;
+                // Update non rebasing supply
+                nonRebasingSupply = nonRebasingSupply.add(balanceOf(_account));
+                // Update credit tallies
+                rebasingCredits = rebasingCredits.sub(
+                    _creditBalances[_account]
+                );
+            }
         }
     }
 

contracts/package.json

@@ -22,7 +22,7 @@
     "echidna": "yarn run clean && echidna-test . --contract PropertiesOUSDTransferable --config contracts/crytic/TestOUSDTransferable.yaml",
     "compute-merkle-proofs-local": "HARDHAT_NETWORK=localhost node scripts/staking/airDrop.js reimbursements.csv scripts/staking/merkleProofedAccountsToBeCompensated.json && cp scripts/staking/merkleProofedAccountsToBeCompensated.json ../dapp/src/constants/merkleProofedAccountsToBeCompensated.json",
     "compute-merkle-proofs-mainnet": "HARDHAT_NETWORK=mainnet node scripts/staking/airDrop.js reimbursements.csv scripts/staking/merkleProofedAccountsToBeCompensated.json && cp scripts/staking/merkleProofedAccountsToBeCompensated.json ../dapp/src/constants/merkleProofedAccountsToBeCompensated.json",
-    "slither": "yarn run clean && slither . --filter-paths \"crytic|mocks|@openzeppelin\" --exclude-low --exclude-informational --exclude conformance-to-solidity-naming-conventions,different-pragma-directives-are-used,external-function,assembly",
+    "slither": "yarn run clean && slither . --filter-paths \"crytic|mocks|@openzeppelin\" --exclude-low --exclude-informational --exclude conformance-to-solidity-naming-conventions,different-pragma-directives-are-used,external-function,assembly,incorrect-equality",
     "clean": "rm -rf build crytic-export artifacts cache deployments/local*"
   },
   "author": "Origin Protocol Inc <support@originprotocol.com>",

contracts/test/token.js

@@ -828,4 +828,51 @@ describe("Token", function () {
       await ousd.totalSupply()
     );
   });
+
+  it("Should exact transfer to new contract accounts", async () => {
+    let { ousd, vault, matt, usdc, mockNonRebasing } = await loadFixture(
+      defaultFixture
+    );
+
+    // Add yield to so we need higher resolution
+    await usdc.connect(matt).mint(usdcUnits("9671.2345"));
+    await usdc.connect(matt).transfer(vault.address, usdcUnits("9671.2345"));
+    await vault.rebase();
+
+    // Helper to verify balance-exact transfers in
+    const checkTransferIn = async (amount) => {
+      const beforeReceiver = await ousd.balanceOf(mockNonRebasing.address);
+      await ousd.connect(matt).transfer(mockNonRebasing.address, amount);
+      const afterReceiver = await ousd.balanceOf(mockNonRebasing.address);
+      expect(beforeReceiver.add(amount)).to.equal(afterReceiver);
+    };
+
+    // Helper to verify balance-exact transfers out
+    const checkTransferOut = async (amount) => {
+      const beforeReceiver = await ousd.balanceOf(mockNonRebasing.address);
+      await mockNonRebasing.transfer(matt.address, amount);
+      const afterReceiver = await ousd.balanceOf(mockNonRebasing.address);
+      expect(beforeReceiver.sub(amount)).to.equal(afterReceiver);
+    };
+
+    // In
+    await checkTransferIn(1);
+    await checkTransferIn(2);
+    await checkTransferIn(5);
+    await checkTransferIn(9);
+    await checkTransferIn(100);
+    await checkTransferIn(2);
+    await checkTransferIn(5);
+    await checkTransferIn(9);
+
+    // Out
+    await checkTransferOut(1);
+    await checkTransferOut(2);
+    await checkTransferOut(5);
+    await checkTransferOut(9);
+    await checkTransferOut(100);
+    await checkTransferOut(2);
+    await checkTransferOut(5);
+    await checkTransferOut(9);
+  });
 });