Also enforce minimum of 30Gwei priority fee

src/gasPriceOracle/adapters/polygon.ts

@@ -1,6 +1,6 @@
 import { providers } from "ethers";
 import { BaseHTTPAdapter, BaseHTTPAdapterArgs } from "../../priceClient/adapters/baseAdapter";
-import { bnZero, isDefined, parseUnits } from "../../utils";
+import { BigNumber, bnZero, isDefined, parseUnits } from "../../utils";
 import { CHAIN_IDs } from "../../constants";
 import { GasPriceEstimate } from "../types";
 import { gasPriceError } from "../util";
@@ -67,12 +67,25 @@ class PolygonGasStation extends BaseHTTPAdapter {
   }
 }
 
-export function gasStation(provider: providers.Provider, chainId: number): Promise<GasPriceEstimate> {
+export async function gasStation(provider: providers.Provider, chainId: number): Promise<GasPriceEstimate> {
   const gasStation = new PolygonGasStation({ chainId: chainId, timeout: 2000, retries: 0 });
+  let maxPriorityFeePerGas: BigNumber;
+  let maxFeePerGas: BigNumber;
   try {
-    return gasStation.getFeeData();
+    ({ maxPriorityFeePerGas, maxFeePerGas } = await gasStation.getFeeData());
   } catch (err) {
     // Fall back to the RPC provider. May be less accurate.
-    return eip1559(provider, chainId);
+    ({ maxPriorityFeePerGas, maxFeePerGas } = await eip1559(provider, chainId));
+
+    // Per the GasStation docs, the minimum priority fee on Polygon is 30 Gwei.
+    // https://docs.polygon.technology/tools/gas/polygon-gas-station/#interpretation
+    const minPriorityFee = parseUnits("30", 9);
+    if (maxPriorityFeePerGas.lt(minPriorityFee)) {
+      const priorityDelta = minPriorityFee.sub(maxPriorityFeePerGas);
+      maxPriorityFeePerGas = minPriorityFee;
+      maxFeePerGas = maxFeePerGas.add(priorityDelta);
+    }
   }
+
+  return { maxPriorityFeePerGas, maxFeePerGas };
 }