fix: enforce a minimum of 1 GRT when delegating to an indexer for the first time

Author: pcarranzav

contracts/staking/StakingExtension.sol

@@ -26,6 +26,8 @@ contract StakingExtension is StakingV4Storage, GraphUpgradeable, IStakingExtensi
 
     /// @dev 100% in parts per million
     uint32 private constant MAX_PPM = 1000000;
+    /// @dev Minimum delegation for the first delegator of an indexer
+    uint256 private constant MINIMUM_DELEGATION = 1e18;
 
     /**
      * @dev Check if the caller is the slasher.
@@ -544,9 +546,13 @@ contract StakingExtension is StakingV4Storage, GraphUpgradeable, IStakingExtensi
         uint256 delegatedTokens = _tokens.sub(delegationTax);
 
         // Calculate shares to issue
-        uint256 shares = (pool.tokens == 0)
-            ? delegatedTokens
-            : delegatedTokens.mul(pool.shares).div(pool.tokens);
+        uint256 shares;
+        if (pool.tokens == 0) {
+            require(_tokens >= MINIMUM_DELEGATION, "!minimum-delegation");
+            shares = delegatedTokens;
+        } else {
+            shares = delegatedTokens.mul(pool.shares).div(pool.tokens);
+        }
         require(shares > 0, "!shares");
 
         // Update the delegation pool

test/staking/delegation.test.ts

@@ -372,6 +372,17 @@ describe('Staking::Delegation', () => {
         await expect(tx).revertedWith('!tokens')
       })
 
+      it('reject delegate with less than 1 GRT when the pool is not initialized', async function () {
+        const tokensToDelegate = toGRT('0.5')
+        const tx = staking.connect(delegator.signer).delegate(indexer.address, tokensToDelegate)
+        await expect(tx).revertedWith('!minimum-delegation')
+      })
+
+      it('allows delegating under 1 GRT when the pool is initialized', async function () {
+        await shouldDelegate(delegator, toGRT('1'))
+        await shouldDelegate(delegator, toGRT('0.01'))
+      })
+
       it('reject delegate to empty address', async function () {
         const tokensToDelegate = toGRT('100')
         const tx = staking.connect(delegator.signer).delegate(AddressZero, tokensToDelegate)