fix: dont block trade when price impact is favorable (#6261)

* fix: dont block trade when price impact is favorable

* fix: add comment

src/utils/prices.test.ts

@@ -122,6 +122,9 @@ describe('prices', () => {
     it('0 for undefined', () => {
       expect(warningSeverity(undefined)).toEqual(0)
     })
+    it('0 for negative', () => {
+      expect(warningSeverity(new Percent(-1))).toEqual(0)
+    })
     it('correct for 0', () => {
       expect(warningSeverity(new Percent(0))).toEqual(0)
     })

src/utils/prices.ts

@@ -85,6 +85,12 @@ const IMPACT_TIERS = [
 type WarningSeverity = 0 | 1 | 2 | 3 | 4
 export function warningSeverity(priceImpact: Percent | undefined): WarningSeverity {
   if (!priceImpact) return 0
+  // This function is used to calculate the Severity level for % changes in USD value and Price Impact.
+  // Price Impact is always an absolute value (conceptually always negative, but represented in code with a positive value)
+  // The USD value change can be positive or negative, and it follows the same standard as Price Impact (positive value is the typical case of a loss due to slippage).
+  // We don't want to return a warning level for a favorable/profitable change, so when the USD value change is negative we return 0.
+  // TODO (WEB-3133): Disambiguate Price Impact and USD value change, and flip the sign of USD Value change.
+  if (priceImpact.lessThan(0)) return 0
   let impact: WarningSeverity = IMPACT_TIERS.length as WarningSeverity
   for (const impactLevel of IMPACT_TIERS) {
     if (impactLevel.lessThan(priceImpact)) return impact