Refactor makeTestResults function to use a stack for traversal

CHANGELOG.md

@@ -27,6 +27,7 @@
 - `[babel-plugin-jest-hoist]` Use `denylist` instead of the deprecated `blacklist` for Babel 8 support ([#14109](https://github.com/jestjs/jest/pull/14109))
 - `[expect]` Check error instance type for `toThrow/toThrowError` ([#14576](https://github.com/jestjs/jest/pull/14576))
 - `[jest-circus]` [**BREAKING**] Prevent false test failures caused by promise rejections handled asynchronously ([#14315](https://github.com/jestjs/jest/pull/14315))
+- `[jest-circus]` Replace recursive `makeTestResults` implementation with iterative one ([#14760](https://github.com/jestjs/jest/pull/14760))
 - `[jest-circus, jest-expect, jest-snapshot]` Pass `test.failing` tests when containing failing snapshot matchers ([#14313](https://github.com/jestjs/jest/pull/14313))
 - `[jest-cli]` [**BREAKING**] Validate CLI flags that require arguments receives them ([#14783](https://github.com/jestjs/jest/pull/14783))
 - `[jest-config]` Make sure to respect `runInBand` option ([#14578](https://github.com/jestjs/jest/pull/14578))

packages/jest-circus/src/__tests__/utils.test.ts

@@ -0,0 +1,24 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+import {runTest} from '../__mocks__/testUtils';
+
+test('makeTestResults does not thrown a stack overflow exception', () => {
+  let testString = 'describe("top level describe", () => {';
+  const numberOfTestBlocks = 150_000;
+  let currentTestIndex = 0;
+
+  while (currentTestIndex < numberOfTestBlocks) {
+    testString += `test("should do something #${currentTestIndex++}", () => {});`;
+  }
+
+  testString += '})';
+
+  const {stdout} = runTest(testString);
+
+  expect(stdout.split('\n')).toHaveLength(900_010);
+});

packages/jest-circus/src/utils.ts

@@ -391,17 +391,22 @@ export const makeSingleTestResult = (
 const makeTestResults = (
   describeBlock: Circus.DescribeBlock,
 ): Circus.TestResults => {
-  const testResults: Circus.TestResults = [];
+  const testResults = [];
+  const stack: [[Circus.DescribeBlock, number]] = [[describeBlock, 0]];
 
-  for (const child of describeBlock.children) {
-    switch (child.type) {
-      case 'describeBlock': {
-        testResults.push(...makeTestResults(child));
+  while (stack.length > 0) {
+    const [currentBlock, childIndex] = stack.pop()!;
+
+    for (let i = childIndex; i < currentBlock.children.length; i++) {
+      const child = currentBlock.children[i];
+
+      if (child.type === 'describeBlock') {
+        stack.push([currentBlock, i + 1]);
+        stack.push([child, 0]);
         break;
       }
-      case 'test': {
+      if (child.type === 'test') {
         testResults.push(makeSingleTestResult(child));
-        break;
       }
     }
   }