Fix liquidity migration bug

[oveddan]

Summary

FIXED: Resolves critical hook migration bug that caused CannotUpdateEmptyPosition() errors when migrating from hooks that store two positions in the same ticks.

Bug Description

Location: V4Liquidity.burnPositions() function
Error: CannotUpdateEmptyPosition()
Cause: Function attempted to modify positions with liquidityDelta: 0 on already-empty positions

Root Cause Analysis

The migration logic tried to burn positions that had zero liquidity, causing Uniswap V4's position validation to reject the operation:

// In Position.sol - the validation that was failing:
if (liquidityDelta == 0) {
    if (liquidity == 0) CannotUpdateEmptyPosition.selector.revertWith(); // ← This error
}

This can happen when we initial a hook for a coin, and our initial liquidity position calculations result in adding liquidity twice to a position with the same ticks.

This behavior can be seen in the uniswap Position.t.sol test:

    function test_fuzz_update(
        int128 liquidityDelta,
        Position.State memory pos,
        uint256 newFeeGrowthInside0X128,
        uint256 newFeeGrowthInside1X128
    ) public {
        Position.State storage position = positions[0];
        position.liquidity = pos.liquidity;
        position.feeGrowthInside0LastX128 = pos.feeGrowthInside0LastX128;
        position.feeGrowthInside1LastX128 = pos.feeGrowthInside1LastX128;

        uint128 oldLiquidity = position.liquidity;

        if (position.liquidity == 0 && liquidityDelta == 0) {
            vm.expectRevert(Position.CannotUpdateEmptyPosition.selector);
        }
}

Fix Applied

Added empty position check in V4Liquidity.sol line ~201-210:

// Skip positions that have no liquidity to avoid CannotUpdateEmptyPosition error  
if (liquidity == 0) {
    burnedPositions[i] = BurnedPosition({
        tickLower: positions[i].tickLower,
        tickUpper: positions[i].tickUpper, 
        amount0Received: 0,
        amount1Received: 0
    });
    continue; // Skip the modifyLiquidity call
}

Impact Resolved

• ✅ Hook version 1.1.2 migrations now work for both content and creator coins
• ✅ Production coins can upgrade from problematic hook versions
• ✅ No more blocked upgrade paths for existing users
• ✅ Backward compatibility maintained for all valid positions

🤖 Generated with Claude Code