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Flash example checkpoint (Uniswap#132)
* final checkpoint tests pass * fix: minor edits * Fix code style issues with Prettier * fix flash contract fix migrator tests * update snaps Co-authored-by: Lint Action <[email protected]> Co-authored-by: Noah Zinsmeister <[email protected]>
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‎contracts/examples/PairFlash.sol

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// SPDX-License-Identifier: GPL-2.0-or-later
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pragma solidity =0.7.6;
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pragma abicoder v2;
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import '@uniswap/v3-core/contracts/interfaces/callback/IUniswapV3FlashCallback.sol';
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import '@uniswap/v3-core/contracts/libraries/LowGasSafeMath.sol';
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import '../base/PeripheryPayments.sol';
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import '../base/PeripheryImmutableState.sol';
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import '../libraries/PoolAddress.sol';
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import '../libraries/CallbackValidation.sol';
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import '../libraries/TransferHelper.sol';
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import '../interfaces/ISwapRouter.sol';
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/// @title Flash contract implementation
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/// @notice An example contract using the Uniswap V3 flash function
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contract PairFlash is IUniswapV3FlashCallback, PeripheryPayments {
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using LowGasSafeMath for uint256;
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using LowGasSafeMath for int256;
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ISwapRouter public immutable swapRouter;
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constructor(
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ISwapRouter _swapRouter,
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address _factory,
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address _WETH9
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) PeripheryImmutableState(_factory, _WETH9) {
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swapRouter = _swapRouter;
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}
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// fee2 and fee3 are the two other fees associated with the two other pools of token0 and token1
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struct FlashCallbackData {
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uint256 amount0;
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uint256 amount1;
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address payer;
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PoolAddress.PoolKey poolKey;
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uint24 poolFee2;
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uint24 poolFee3;
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}
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/// @param fee0 The fee from calling flash for token0
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/// @param fee1 The fee from calling flash for token1
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/// @param data The data needed in the callback passed as FlashCallbackData from `initFlash`
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/// @notice implements the callback called from flash
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/// @dev fails if the flash is not profitable, meaning the amountOut from the flash is less than the amount borrowed
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function uniswapV3FlashCallback(
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uint256 fee0,
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uint256 fee1,
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bytes calldata data
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) external override {
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FlashCallbackData memory decoded = abi.decode(data, (FlashCallbackData));
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CallbackValidation.verifyCallback(factory, decoded.poolKey);
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address token0 = decoded.poolKey.token0;
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address token1 = decoded.poolKey.token1;
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// profitability parameters - we must receive at least the required payment from the arbitrage swaps
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// exactInputSingle will fail if this amount not met
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uint256 amount0Min = LowGasSafeMath.add(decoded.amount0, fee0);
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uint256 amount1Min = LowGasSafeMath.add(decoded.amount1, fee1);
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// call exactInputSingle for swapping token1 for token0 in pool with fee2
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TransferHelper.safeApprove(token1, address(swapRouter), decoded.amount1);
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uint256 amountOut0 =
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swapRouter.exactInputSingle(
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ISwapRouter.ExactInputSingleParams({
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tokenIn: token1,
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tokenOut: token0,
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fee: decoded.poolFee2,
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recipient: address(this),
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deadline: block.timestamp,
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amountIn: decoded.amount1,
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amountOutMinimum: amount0Min,
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sqrtPriceLimitX96: 0
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})
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);
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// call exactInputSingle for swapping token0 for token 1 in pool with fee3
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TransferHelper.safeApprove(token0, address(swapRouter), decoded.amount0);
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uint256 amountOut1 =
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swapRouter.exactInputSingle(
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ISwapRouter.ExactInputSingleParams({
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tokenIn: token0,
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tokenOut: token1,
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fee: decoded.poolFee3,
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recipient: address(this),
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deadline: block.timestamp,
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amountIn: decoded.amount0,
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amountOutMinimum: amount1Min,
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sqrtPriceLimitX96: 0
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})
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);
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// end up with amountOut0 of token0 from first swap and amountOut1 of token1 from second swap
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uint256 amount0Owed = LowGasSafeMath.add(decoded.amount0, fee0);
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uint256 amount1Owed = LowGasSafeMath.add(decoded.amount1, fee1);
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// pay the required amounts back to the pair
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if (amount0Min > 0) pay(token0, address(this), msg.sender, amount0Min);
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if (amount1Min > 0) pay(token1, address(this), msg.sender, amount1Min);
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// if profitable pay profits to payer
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if (amountOut0 > amount0Owed) {
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uint256 profit0 = amountOut0 - amount0Owed;
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pay(token0, address(this), decoded.payer, profit0);
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}
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if (amountOut1 > amount1Owed) {
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uint256 profit1 = amountOut1 - amount1Owed;
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pay(token1, address(this), decoded.payer, profit1);
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}
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}
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//fee1 is the fee of the pool from the initial borrow
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//fee2 is the fee of the first pool to arb from
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//fee3 is the fee of the second pool to arb from
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struct FlashParams {
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address token0;
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address token1;
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uint24 fee1;
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uint256 amount0;
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uint256 amount1;
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uint24 fee2;
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uint24 fee3;
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}
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/// @param params The parameters necessary for flash and the callback, passed in as FlashParams
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/// @notice Calls the pools flash function with data needed in `uniswapV3FlashCallback`
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function initFlash(FlashParams memory params) external {
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PoolAddress.PoolKey memory poolKey =
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PoolAddress.PoolKey({token0: params.token0, token1: params.token1, fee: params.fee1});
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IUniswapV3Pool pool = IUniswapV3Pool(PoolAddress.computeAddress(factory, poolKey));
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// recipient of borrowed amounts
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// amount of token0 requested to borrow
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// amount of token1 requested to borrow
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// need amount 0 and amount1 in callback to pay back pool
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// recipient of flash should be THIS contract
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pool.flash(
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address(this),
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params.amount0,
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params.amount1,
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abi.encode(
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FlashCallbackData({
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amount0: params.amount0,
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amount1: params.amount1,
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payer: msg.sender,
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poolKey: poolKey,
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poolFee2: params.fee2,
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poolFee3: params.fee3
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})
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)
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);
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}
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}

‎test/PairFlash.spec.ts

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import { ethers, waffle } from 'hardhat'
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import { BigNumber, constants, Contract, ContractTransaction } from 'ethers'
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import {
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IWETH9,
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MockTimeNonfungiblePositionManager,
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MockTimeSwapRouter,
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PairFlash,
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IUniswapV3Pool,
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TestERC20,
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TestERC20Metadata,
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IUniswapV3Factory,
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NFTDescriptor,
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Quoter,
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SwapRouter,
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} from '../typechain'
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import completeFixture from './shared/completeFixture'
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import { FeeAmount, MaxUint128, TICK_SPACINGS } from './shared/constants'
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import { encodePriceSqrt } from './shared/encodePriceSqrt'
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import snapshotGasCost from './shared/snapshotGasCost'
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import { expect } from './shared/expect'
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import { getMaxTick, getMinTick } from './shared/ticks'
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import { computePoolAddress } from './shared/computePoolAddress'
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describe('PairFlash test', () => {
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const provider = waffle.provider
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const wallets = waffle.provider.getWallets()
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const wallet = wallets[0]
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let flash: PairFlash
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let nft: MockTimeNonfungiblePositionManager
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let token0: TestERC20
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let token1: TestERC20
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let factory: IUniswapV3Factory
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let quoter: Quoter
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async function createPool(tokenAddressA: string, tokenAddressB: string, fee: FeeAmount, price: BigNumber) {
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if (tokenAddressA.toLowerCase() > tokenAddressB.toLowerCase())
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[tokenAddressA, tokenAddressB] = [tokenAddressB, tokenAddressA]
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await nft.createAndInitializePoolIfNecessary(tokenAddressA, tokenAddressB, fee, price)
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const liquidityParams = {
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token0: tokenAddressA,
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token1: tokenAddressB,
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fee: fee,
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tickLower: getMinTick(TICK_SPACINGS[fee]),
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tickUpper: getMaxTick(TICK_SPACINGS[fee]),
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recipient: wallet.address,
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amount0Desired: 1000000,
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amount1Desired: 1000000,
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amount0Min: 0,
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amount1Min: 0,
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deadline: 1,
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}
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return nft.mint(liquidityParams)
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}
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const flashFixture = async () => {
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const { router, tokens, factory, weth9, nft } = await completeFixture(wallets, provider)
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const token0 = tokens[0]
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const token1 = tokens[1]
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const flashContractFactory = await ethers.getContractFactory('PairFlash')
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const flash = (await flashContractFactory.deploy(router.address, factory.address, weth9.address)) as PairFlash
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const quoterFactory = await ethers.getContractFactory('Quoter')
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const quoter = (await quoterFactory.deploy(factory.address, weth9.address)) as Quoter
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return {
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token0,
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token1,
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flash,
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factory,
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weth9,
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nft,
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quoter,
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router,
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}
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}
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let loadFixture: ReturnType<typeof waffle.createFixtureLoader>
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before('create fixture loader', async () => {
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loadFixture = waffle.createFixtureLoader(wallets)
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})
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beforeEach('load fixture', async () => {
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;({ factory, token0, token1, flash, nft, quoter } = await loadFixture(flashFixture))
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await token0.approve(nft.address, MaxUint128)
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await token1.approve(nft.address, MaxUint128)
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await createPool(token0.address, token1.address, FeeAmount.LOW, encodePriceSqrt(5, 10))
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await createPool(token0.address, token1.address, FeeAmount.MEDIUM, encodePriceSqrt(1, 1))
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await createPool(token0.address, token1.address, FeeAmount.HIGH, encodePriceSqrt(20, 10))
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})
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describe('flash', () => {
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it('test correct transfer events', async () => {
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//choose amountIn to test
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const amount0In = 1000
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const amount1In = 1000
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const fee0 = Math.ceil((amount0In * FeeAmount.MEDIUM) / 1000000)
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const fee1 = Math.ceil((amount1In * FeeAmount.MEDIUM) / 1000000)
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const flashParams = {
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token0: token0.address,
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token1: token1.address,
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fee1: FeeAmount.MEDIUM,
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amount0: amount0In,
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amount1: amount1In,
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fee2: FeeAmount.LOW,
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fee3: FeeAmount.HIGH,
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}
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// pool1 is the borrow pool
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const pool1 = computePoolAddress(factory.address, [token0.address, token1.address], FeeAmount.MEDIUM)
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const pool2 = computePoolAddress(factory.address, [token0.address, token1.address], FeeAmount.LOW)
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const pool3 = computePoolAddress(factory.address, [token0.address, token1.address], FeeAmount.HIGH)
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const expectedAmountOut0 = await quoter.callStatic.quoteExactInputSingle(
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token1.address,
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token0.address,
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FeeAmount.LOW,
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amount1In,
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encodePriceSqrt(20, 10)
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)
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const expectedAmountOut1 = await quoter.callStatic.quoteExactInputSingle(
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token0.address,
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token1.address,
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FeeAmount.HIGH,
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amount0In,
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encodePriceSqrt(5, 10)
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)
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await expect(flash.initFlash(flashParams))
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.to.emit(token0, 'Transfer')
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.withArgs(pool1, flash.address, amount0In)
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.to.emit(token1, 'Transfer')
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.withArgs(pool1, flash.address, amount1In)
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.to.emit(token0, 'Transfer')
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.withArgs(pool2, flash.address, expectedAmountOut0)
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.to.emit(token1, 'Transfer')
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.withArgs(pool3, flash.address, expectedAmountOut1)
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.to.emit(token0, 'Transfer')
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.withArgs(flash.address, wallet.address, expectedAmountOut0.toNumber() - amount0In - fee0)
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.to.emit(token1, 'Transfer')
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.withArgs(flash.address, wallet.address, expectedAmountOut1.toNumber() - amount1In - fee1)
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})
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it('gas', async () => {
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const amount0In = 1000
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const amount1In = 1000
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const flashParams = {
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token0: token0.address,
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token1: token1.address,
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fee1: FeeAmount.MEDIUM,
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amount0: amount0In,
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amount1: amount1In,
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fee2: FeeAmount.LOW,
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fee3: FeeAmount.HIGH,
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}
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await snapshotGasCost(flash.initFlash(flashParams))
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})
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})
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})

‎test/V3Migrator.spec.ts

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let loadFixture: ReturnType<typeof waffle.createFixtureLoader>
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const expectedLiquidity = 10000 - 1000
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before('create fixture loader', async () => {
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const wallets = await (ethers as any).getSigners()
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wallet = wallets[0]
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;({ factoryV2, factoryV3, token, weth9, nft, migrator } = await loadFixture(migratorFixture))
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})
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beforeEach('add V2 liquidity', async () => {
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await factoryV2.createPair(token.address, weth9.address)
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const pairAddress = await factoryV2.getPair(token.address, weth9.address)
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pair = new ethers.Contract(pairAddress, PAIR_V2_ABI, wallet) as IUniswapV2Pair
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await token.transfer(pair.address, 10000)
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await weth9.transfer(pair.address, 10000)
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await pair.mint(wallet.address)
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expect(await pair.balanceOf(wallet.address)).to.be.eq(expectedLiquidity)
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})
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afterEach('ensure allowances are cleared', async () => {
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const allowanceToken = await token.allowance(migrator.address, nft.address)
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const allowanceWETH9 = await weth9.allowance(migrator.address, nft.address)
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describe('#migrate', () => {
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let tokenLower: boolean
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const expectedLiquidity = 10000 - 1000
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beforeEach(() => {
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tokenLower = token.address.toLowerCase() < weth9.address.toLowerCase()
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})
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beforeEach('add V2 liquidity', async () => {
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await factoryV2.createPair(token.address, weth9.address)
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const pairAddress = await factoryV2.getPair(token.address, weth9.address)
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pair = new ethers.Contract(pairAddress, PAIR_V2_ABI, wallet) as IUniswapV2Pair
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await token.transfer(pair.address, 10000)
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await weth9.transfer(pair.address, 10000)
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await pair.mint(wallet.address)
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expect(await pair.balanceOf(wallet.address)).to.be.eq(expectedLiquidity)
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})
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it('fails if v3 pool is not initialized', async () => {
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await pair.approve(migrator.address, expectedLiquidity)
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await expect(

‎test/__snapshots__/PairFlash.spec.ts.snap

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// Jest Snapshot v1, https://goo.gl/fbAQLP
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exports[`PairFlash test flash gas 1`] = `334941`;

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