From c676ecb8cfce2c06c2d9a4214b028b70735a94b2 Mon Sep 17 00:00:00 2001
From: Greg Hysen <greg.hysen@gmail.com>
Date: Tue, 22 Oct 2019 11:53:00 -0700
Subject: [PATCH] Force no-op when moving zero stake or moving from undelegated
 to undelegated.

---
 .../staking/contracts/src/stake/MixinStake.sol | 11 +++++++++++
 .../staking/test/unit_tests/stake_test.ts      | 18 +++++++++++++-----
 2 files changed, 24 insertions(+), 5 deletions(-)

diff --git a/contracts/staking/contracts/src/stake/MixinStake.sol b/contracts/staking/contracts/src/stake/MixinStake.sol
index 415792238e..c0b11bbd86 100644
--- a/contracts/staking/contracts/src/stake/MixinStake.sol
+++ b/contracts/staking/contracts/src/stake/MixinStake.sol
@@ -111,6 +111,17 @@ contract MixinStake is
     {
         address staker = msg.sender;
 
+        // Sanity check: no-op if no stake is being moved.
+        if (amount == 0) {
+            return;
+        }
+
+        // Sanity check: no-op if moving stake from undelegated to undelegated.
+        if (from.status == IStructs.StakeStatus.UNDELEGATED &&
+            to.status == IStructs.StakeStatus.UNDELEGATED) {
+            return;
+        }
+
         // handle delegation
         if (from.status == IStructs.StakeStatus.DELEGATED) {
             _undelegateStake(
diff --git a/contracts/staking/test/unit_tests/stake_test.ts b/contracts/staking/test/unit_tests/stake_test.ts
index a4b84fd251..76e5dd5d47 100644
--- a/contracts/staking/test/unit_tests/stake_test.ts
+++ b/contracts/staking/test/unit_tests/stake_test.ts
@@ -373,7 +373,7 @@ blockchainTests.resets('MixinStake unit tests', env => {
             expect(increaseNextBalanceEvents).to.be.length(0);
         });
 
-        it('moves the owner stake between the same pointer when both are undelegated', async () => {
+        it('does nothing when moving the owner stake from undelegated to undelegated', async () => {
             const amount = getRandomInteger(0, 100e18);
             const { logs } = await testContract.moveStake.awaitTransactionSuccessAsync(
                 { status: StakeStatus.Undelegated, poolId: VALID_POOL_IDS[0] },
@@ -381,10 +381,18 @@ blockchainTests.resets('MixinStake unit tests', env => {
                 amount,
             );
             const events = filterLogsToArguments<MoveStakeStorageEventArgs>(logs, StakeEvents.MoveStakeStorage);
-            expect(events).to.be.length(1);
-            expect(events[0].fromBalanceSlot).to.eq(stakerUndelegatedStakeSlot);
-            expect(events[0].toBalanceSlot).to.eq(stakerUndelegatedStakeSlot);
-            expect(events[0].amount).to.bignumber.eq(amount);
+            expect(events).to.be.length(0);
+        });
+
+        it('does nothing when moving zero stake', async () => {
+            const amount = new BigNumber(0);
+            const { logs } = await testContract.moveStake.awaitTransactionSuccessAsync(
+                { status: StakeStatus.Delegated, poolId: VALID_POOL_IDS[0] },
+                { status: StakeStatus.Delegated, poolId: VALID_POOL_IDS[1] },
+                amount,
+            );
+            const events = filterLogsToArguments<MoveStakeStorageEventArgs>(logs, StakeEvents.MoveStakeStorage);
+            expect(events).to.be.length(0);
         });
 
         it('moves the owner stake between the same pointer when both are delegated', async () => {