Quick fix to #800

src/components/swap/confirmPriceImpactWithoutFee.ts

+// gathers additional user consent for a high price impact
+import { Percent } from '@uniswap/sdk'
+import { ALLOWED_PRICE_IMPACT_HIGH, PRICE_IMPACT_WITHOUT_FEE_CONFIRM_MIN } from '../../constants'
+
+export default function confirmPriceImpactWithoutFee(priceImpactWithoutFee: Percent): boolean {
+  if (!priceImpactWithoutFee.lessThan(PRICE_IMPACT_WITHOUT_FEE_CONFIRM_MIN)) {
+    return (
+      window.prompt(
+        `This swap has a price impact of at least ${PRICE_IMPACT_WITHOUT_FEE_CONFIRM_MIN.toFixed(
+          0
+        )}%. Please type the word "confirm" to continue with this swap.`
+      ) === 'confirm'
+    )
+  } else if (!priceImpactWithoutFee.lessThan(ALLOWED_PRICE_IMPACT_HIGH)) {
+    return window.confirm(
+      `This swap has a price impact of at least ${ALLOWED_PRICE_IMPACT_HIGH.toFixed(
+        0
+      )}%. Please confirm that you would like to continue with this swap.`
+    )
+  }
+  return true
+}

src/constants/index.ts

@@ -111,10 +111,15 @@ export const DEFAULT_DEADLINE_FROM_NOW = 60 * 15
 
 // one basis point
 export const ONE_BIPS = new Percent(JSBI.BigInt(1), JSBI.BigInt(10000))
+export const BIPS_BASE = JSBI.BigInt(10000)
 // used for warning states
-export const ALLOWED_SLIPPAGE_LOW: Percent = new Percent(JSBI.BigInt(100), JSBI.BigInt(10000))
-export const ALLOWED_SLIPPAGE_MEDIUM: Percent = new Percent(JSBI.BigInt(500), JSBI.BigInt(10000))
-export const ALLOWED_SLIPPAGE_HIGH: Percent = new Percent(JSBI.BigInt(1000), JSBI.BigInt(10000))
+export const ALLOWED_PRICE_IMPACT_LOW: Percent = new Percent(JSBI.BigInt(100), BIPS_BASE) // 1%
+export const ALLOWED_PRICE_IMPACT_MEDIUM: Percent = new Percent(JSBI.BigInt(500), BIPS_BASE) // 5%
+export const ALLOWED_PRICE_IMPACT_HIGH: Percent = new Percent(JSBI.BigInt(1000), BIPS_BASE) // 10%
+
+// if the price slippage exceeds this number, force the user to type 'confirm' to execute
+export const PRICE_IMPACT_WITHOUT_FEE_CONFIRM_MIN: Percent = new Percent(JSBI.BigInt(2500), BIPS_BASE) // 25%
+
 // used to ensure the user doesn't send so much ETH so they end up with <.01
 export const MIN_ETH: JSBI = JSBI.exponentiate(JSBI.BigInt(10), JSBI.BigInt(16)) // .01 ETH
 export const V1_TRADE_LINK_THRESHOLD = new Percent(JSBI.BigInt(50), JSBI.BigInt(10000))

src/pages/Send/index.tsx

@@ -14,6 +14,7 @@ import CurrencyInputPanel from '../../components/CurrencyInputPanel'
 import QuestionHelper from '../../components/Question'
 import { AutoRow, RowBetween, RowFixed } from '../../components/Row'
 import AdvancedSwapDetailsDropdown from '../../components/swap/AdvancedSwapDetailsDropdown'
+import confirmPriceImpactWithoutFee from '../../components/swap/confirmPriceImpactWithoutFee'
 import FormattedPriceImpact from '../../components/swap/FormattedPriceImpact'
 import SwapModalFooter from '../../components/swap/SwapModalFooter'
 import { ArrowWrapper, BottomGrouping, Dots, InputGroup, StyledNumerical, Wrapper } from '../../components/swap/styleds'
@@ -134,6 +135,10 @@ export default function Send({ location: { search } }: RouteComponentProps) {
   const swapCallback = useSwapCallback(bestTrade, allowedSlippage, deadline, recipient)
 
   function onSwap() {
+    if (priceImpactWithoutFee && !confirmPriceImpactWithoutFee(priceImpactWithoutFee)) {
+      return
+    }
+
     setAttemptingTxn(true)
     swapCallback().then(hash => {
       setTxHash(hash)

src/pages/Swap/index.tsx

@@ -13,9 +13,11 @@ import CurrencyInputPanel from '../../components/CurrencyInputPanel'
 import QuestionHelper from '../../components/Question'
 import { RowBetween, RowFixed } from '../../components/Row'
 import AdvancedSwapDetailsDropdown from '../../components/swap/AdvancedSwapDetailsDropdown'
+import confirmPriceImpactWithoutFee from '../../components/swap/confirmPriceImpactWithoutFee'
 import FormattedPriceImpact from '../../components/swap/FormattedPriceImpact'
 import { ArrowWrapper, BottomGrouping, Dots, Wrapper } from '../../components/swap/styleds'
 import SwapModalFooter from '../../components/swap/SwapModalFooter'
+import SwapModalHeader from '../../components/swap/SwapModalHeader'
 import TradePrice from '../../components/swap/TradePrice'
 import V1TradeLink from '../../components/swap/V1TradeLink'
 import { DEFAULT_DEADLINE_FROM_NOW, INITIAL_ALLOWED_SLIPPAGE, MIN_ETH } from '../../constants'
@@ -28,7 +30,6 @@ import { useDefaultsFromURL, useDerivedSwapInfo, useSwapActionHandlers, useSwapS
 import { useHasPendingApproval } from '../../state/transactions/hooks'
 import { CursorPointer, TYPE } from '../../theme'
 import { computeSlippageAdjustedAmounts, computeTradePriceBreakdown, warningServerity } from '../../utils/prices'
-import SwapModalHeader from '../../components/swap/SwapModalHeader'
 
 export default function Swap({ location: { search } }: RouteComponentProps) {
   useDefaultsFromURL(search)
@@ -105,7 +106,13 @@ export default function Swap({ location: { search } }: RouteComponentProps) {
   // the callback to execute the swap
   const swapCallback = useSwapCallback(bestTrade, allowedSlippage, deadline)
 
+  const { priceImpactWithoutFee, realizedLPFee } = computeTradePriceBreakdown(bestTrade)
+
   function onSwap() {
+    if (priceImpactWithoutFee && !confirmPriceImpactWithoutFee(priceImpactWithoutFee)) {
+      return
+    }
+
     setAttemptingTxn(true)
     swapCallback().then(hash => {
       setTxHash(hash)
@@ -122,8 +129,6 @@ export default function Swap({ location: { search } }: RouteComponentProps) {
   // errors
   const [showInverted, setShowInverted] = useState<boolean>(false)
 
-  const { priceImpactWithoutFee, realizedLPFee } = computeTradePriceBreakdown(bestTrade)
-
   // warnings on slippage
   const priceImpactSeverity = warningServerity(priceImpactWithoutFee)
 

src/utils/prices.ts

 import { Fraction, JSBI, Percent, TokenAmount, Trade } from '@uniswap/sdk'
-import { ALLOWED_SLIPPAGE_HIGH, ALLOWED_SLIPPAGE_LOW, ALLOWED_SLIPPAGE_MEDIUM } from '../constants'
+import { ALLOWED_PRICE_IMPACT_HIGH, ALLOWED_PRICE_IMPACT_LOW, ALLOWED_PRICE_IMPACT_MEDIUM } from '../constants'
 import { Field } from '../state/swap/actions'
 import { basisPointsToPercent } from './index'
 
@@ -52,9 +52,9 @@ export function computeSlippageAdjustedAmounts(
 }
 
 export function warningServerity(priceImpact: Percent): 0 | 1 | 2 | 3 {
-  if (!priceImpact?.lessThan(ALLOWED_SLIPPAGE_HIGH)) return 3
-  if (!priceImpact?.lessThan(ALLOWED_SLIPPAGE_MEDIUM)) return 2
-  if (!priceImpact?.lessThan(ALLOWED_SLIPPAGE_LOW)) return 1
+  if (!priceImpact?.lessThan(ALLOWED_PRICE_IMPACT_HIGH)) return 3
+  if (!priceImpact?.lessThan(ALLOWED_PRICE_IMPACT_MEDIUM)) return 2
+  if (!priceImpact?.lessThan(ALLOWED_PRICE_IMPACT_LOW)) return 1
   return 0
 }