fix delegation bug

contracts/JoeToken.sol

@@ -63,6 +63,35 @@ contract JoeToken is ERC20("JoeToken", "JOE"), Ownable {
         return _delegates[delegator];
     }
 
+    /**
+     * @notice Transfer `rawAmount` tokens from `msg.sender` to `dst`
+     * @param dst The address of the destination account
+     * @param rawAmount The number of tokens to transfer
+     * @return Whether or not the transfer succeeded
+     */
+    function transfer(address dst, uint256 rawAmount) public override returns (bool) {
+        super.transfer(dst, rawAmount);
+        _moveDelegates(_delegates[msg.sender], _delegates[dst], rawAmount);
+        return true;
+    }
+
+    /**
+     * @notice Transfer `rawAmount` tokens from `src` to `dst`
+     * @param src The address of the source account
+     * @param dst The address of the destination account
+     * @param rawAmount The number of tokens to transfer
+     * @return Whether or not the transfer succeeded
+     */
+    function transferFrom(
+        address src,
+        address dst,
+        uint256 rawAmount
+    ) public override returns (bool) {
+        super.transferFrom(src, dst, rawAmount);
+        _moveDelegates(_delegates[src], _delegates[dst], rawAmount);
+        return true;
+    }
+
     /**
      * @notice Delegate votes from `msg.sender` to `delegatee`
      * @param delegatee The address to delegate votes to

test/JoeToken.test.ts

@@ -70,6 +70,18 @@ describe("JoeToken", function () {
     await this.joe.mint(this.alice.address, "500000000000000000000000000")
   })
 
+  it("should not double spend delegation votes", async function () {
+    await this.joe.mint(this.alice.address, "100")
+    await this.joe.delegate(this.bob.address)
+
+    await this.joe.transfer(this.carol.address, "100")
+    await this.joe.connect(this.carol).delegate(this.bob.address)
+
+    const votes = await this.joe.getCurrentVotes(this.bob.address)
+
+    expect(votes).to.equal("100") // bob should have 100 votes instead of 200
+  })
+
   after(async function () {
     await network.provider.request({
       method: "hardhat_reset",