Negative block number queried when forked network block number is near zero

.changeset/healthy-poems-talk.md

@@ -0,0 +1,5 @@
+---
+"hardhat": patch
+---
+Added logic to use the latest block as the forking block if the difference between the latest block and the max reorganization block is negative.
+This decision is based on the assumption that if the max reorganization block is greater than the latest block then there is a high probability that the fork is occurring on a devnet.

packages/hardhat-core/src/internal/hardhat-network/provider/utils/makeForkClient.ts

@@ -44,7 +44,7 @@ export async function makeForkClient(
   const maxReorg = actualMaxReorg ?? FALLBACK_MAX_REORG;
 
   const latestBlock = await getLatestBlockNumber(provider);
-  const lastSafeBlock = latestBlock - maxReorg;
+  const lastSafeBlock = getLastSafeBlock(latestBlock, maxReorg);
 
   let forkBlockNumber;
   if (forkConfig.blockNumber !== undefined) {
@@ -127,3 +127,12 @@ async function getLatestBlockNumber(provider: HttpProvider) {
   const latestBlock = BigInt(latestBlockString);
   return latestBlock;
 }
+
+export function getLastSafeBlock(
+  latestBlock: bigint,
+  maxReorg: bigint
+): bigint {
+  // Design choice: if latestBlock - maxReorg results in a negative number then the latestBlock block will be used.
+  // This decision is based on the assumption that if maxReorg > latestBlock then there is a high probability that the fork is occurring on a devnet.
+  return latestBlock - maxReorg >= 0 ? latestBlock - maxReorg : latestBlock;
+}

packages/hardhat-core/test/internal/hardhat-network/provider/fork/ForkBlockchain.ts

@@ -10,7 +10,10 @@ import { assert } from "chai";
 import { JsonRpcClient } from "../../../../../src/internal/hardhat-network/jsonrpc/client";
 import { ForkBlockchain } from "../../../../../src/internal/hardhat-network/provider/fork/ForkBlockchain";
 import { randomHashBuffer } from "../../../../../src/internal/hardhat-network/provider/utils/random";
-import { makeForkClient } from "../../../../../src/internal/hardhat-network/provider/utils/makeForkClient";
+import {
+  makeForkClient,
+  getLastSafeBlock,
+} from "../../../../../src/internal/hardhat-network/provider/utils/makeForkClient";
 import { ALCHEMY_URL } from "../../../../setup";
 import {
   createTestLog,
@@ -66,6 +69,17 @@ describe("ForkBlockchain", () => {
     assert.instanceOf(fb, ForkBlockchain);
   });
 
+  describe("getLastSafeBlock", () => {
+    it("should return a safe block that is the difference between the latestBlock and maxReorg", () => {
+      assert.strictEqual(getLastSafeBlock(100n, 50n), 50n);
+      assert.strictEqual(getLastSafeBlock(100n, 100n), 0n); // 0 is a valid fork block number
+    });
+
+    it("should return latestBlock as fork block because the difference between the latestBlock and maxReorg is < 0", () => {
+      assert.strictEqual(getLastSafeBlock(20n, 200n), 20n);
+    });
+  });
+
   describe("getBlock", () => {
     it("can get remote block object by block number", async () => {
       const block = await fb.getBlock(BLOCK_NUMBER_OF_10496585);