fix(expect-utils): iterableEquality should not throw on exotic iterables (#15952)

Author: mhughes2012

CHANGELOG.md

@@ -19,7 +19,8 @@
 
 ### Fixes
 
-- `[expect-utils]` Fix `toStrictEqual` failing on `structuredClone` results due to cross-realm constructor mismatch ([#14011](https://github.com/jestjs/jest/issues/14011))
+- `[expect-utils]` Fix `toStrictEqual` failing on `structuredClone` results due to cross-realm constructor mismatch ([#15959](https://github.com/jestjs/jest/pull/15959))
+- `[@jest/expect-utils]` Prevent `toMatchObject`/subset matching from throwing when encountering exotic iterables ([#15952](https://github.com/jestjs/jest/pull/15952))
 - `[fake-timers]` Convert `Date` to milliseconds before passing to `@sinonjs/fake-timers` ([#16029](https://github.com/jestjs/jest/pull/16029))
 - `[jest-circus]` Prevent crash when `asyncError` is undefined for non-Error throws ([#16003](https://github.com/jestjs/jest/pull/16003))
 - `[jest-circus, jest-jasmine2]` Include `Error.cause` in JSON `failureMessages` output ([#15949](https://github.com/jestjs/jest/issues/15949))

packages/expect-utils/src/__tests__/utils.test.ts

@@ -653,6 +653,18 @@ describe('iterableEquality', () => {
 
     expect(iterableEquality(a, b)).toBe(false);
   });
+
+  test('does not throw when iterating an object with a TypedArray iterator', () => {
+    const badIterable = {
+      [Symbol.iterator]: Uint8Array.prototype[Symbol.iterator],
+    };
+
+    expect(() => iterableEquality(badIterable, badIterable)).not.toThrow();
+    // Returns undefined so equals() can fall through to Object.is / property checks.
+    expect(iterableEquality(badIterable, badIterable)).toBeUndefined();
+    // Same reference must still be considered equal via equals().
+    expect(equals(badIterable, badIterable, [iterableEquality])).toBe(true);
+  });
 });
 
 describe('typeEquality', () => {

packages/expect-utils/src/utils.ts

@@ -303,13 +303,30 @@ export const iterableEquality = (
     }
   }
 
-  const bIterator = b[IteratorSymbol]();
+  let aIterator: Iterator<unknown>;
+  let bIterator: Iterator<unknown>;
+  try {
+    aIterator = a[IteratorSymbol]();
+    bIterator = b[IteratorSymbol]();
+  } catch {
+    // If the iterator factory itself throws (e.g. a TypedArray method used as
+    // [Symbol.iterator] on a plain object), we cannot compare as iterables.
+    // Return undefined so equals() falls through to Object.is / property checks.
+    aStack.pop();
+    bStack.pop();
+    return undefined;
+  }
 
-  for (const aValue of a) {
-    const nextB = bIterator.next();
-    if (nextB.done || !equals(aValue, nextB.value, filteredCustomTesters)) {
+  let aStep = aIterator.next();
+  while (!aStep.done) {
+    const bStep = bIterator.next();
+    if (
+      bStep.done ||
+      !equals(aStep.value, bStep.value, filteredCustomTesters)
+    ) {
       return false;
     }
+    aStep = aIterator.next();
   }
   if (!bIterator.next().done) {
     return false;

packages/expect/src/__tests__/matchers.test.js

@@ -2389,4 +2389,14 @@ describe('toMatchObject()', () => {
       [sym]: true,
     });
   });
+
+  test('does not throw on exotic iterables (e.g. TypedArray iterator on plain object)', () => {
+    const badIterable = {
+      [Symbol.iterator]: Uint8Array.prototype[Symbol.iterator],
+    };
+    expect(() =>
+      jestExpect([badIterable]).toMatchObject([badIterable]),
+    ).not.toThrow();
+    jestExpect([badIterable]).toMatchObject([badIterable]);
+  });
 });