fix proxying .return() on exhausted iterator from some methods of iterator helpers polyfill to the underlying iterator

Author: zloirock

CHANGELOG.md

@@ -9,7 +9,8 @@
 - Wrap `Symbol.for` in `Symbol.prototype.description` polyfill for correct handling of empty string descriptions
 - Fixed one more case (`Iterator.prototype.take`) of a V8 ~ Chromium < 126 [bug](https://issues.chromium.org/issues/336839115)
 - Forced replacement of `Iterator.{ concat, zip, zipKeyed }` in the pure version for ensuring proper wrapped `Iterator` instances as the result
-- Fixed double `.return` calling in case of throwing error in this method in the internal `iterate` helper that affected some polyfills
+- Fixed proxying `.return()` on exhausted iterator from some methods of iterator helpers polyfill to the underlying iterator
+- Fixed double `.return()` calling in case of throwing error in this method in the internal `iterate` helper that affected some polyfills
 - Fixed closing iterator on `IteratorValue` errors in the internal `iterate` helper that affected some polyfills
 - Fixed iterator closing in `Array.from` polyfill on failure to create array property
 - Fixed some cases of iterators closing in `Iterator.{ zip, zipKeyed }` polyfills
@@ -52,9 +53,9 @@
 - Fixed counter in some cases of some `AsyncIterator` methods
 - Fixed order of async iterators closing
 - Fixed iterator closing in `AsyncIterator.prototype.flatMap` polyfill
-- Fixed iterator closing in `AsyncIterator.prototype.map` polyfill on error in inner iterator `.next`
+- Fixed iterator closing in `AsyncIterator.prototype.map` polyfill on error in underlying iterator `.next()`
 - Fixed iterator closing in `AsyncIterator.prototype.take` polyfill with `return: null`
-- Fixed validation `return()` result as object in `AsyncIterator.prototype.take` polyfill
+- Fixed validation `.return()` result as object in `AsyncIterator.prototype.take` polyfill
 - Fixed a lack of error in `structuredClone` polyfill on attempt to transfer multiple objects, some of which are non-transferable
 - Fixed resizable `ArrayBuffer` transferring where `newByteLength` exceeds the original `maxByteLength`
 - Fixed possible loss of symbol enumerability in `Object.defineProperty` in `Symbol` polyfill

packages/core-js/internals/iterator-create-proxy.js

@@ -40,11 +40,13 @@ var createIteratorProxyPrototype = function (IS_ITERATOR) {
     'return': function () {
       var state = getInternalState(this);
       var iterator = state.iterator;
+      var done = state.done;
       state.done = true;
       if (IS_ITERATOR) {
         var returnMethod = getMethod(iterator, 'return');
         return returnMethod ? call(returnMethod, iterator) : createIterResultObject(undefined, true);
       }
+      if (done) return createIterResultObject(undefined, true);
       if (state.inner) try {
         iteratorClose(state.inner.iterator, NORMAL);
       } catch (error) {

tests/unit-global/es.iterator.map.js

@@ -30,6 +30,22 @@ QUnit.test('Iterator#map', assert => {
   const it = createIterator([1], { return() { this.closed = true; } });
   assert.throws(() => map.call(it, {}), TypeError);
   assert.true(it.closed, 'map closes iterator on validation error');
+
+  {
+    let returnCount = 0;
+    const it2 = createIterator([1], {
+      return() {
+        returnCount++;
+        return { done: true, value: undefined };
+      },
+    });
+    const mapped = map.call(it2, x => x);
+    mapped.next();
+    mapped.next(); // exhaust
+    mapped.return();
+    assert.same(returnCount, 0, '.return() on exhausted iterator does not call underlying return');
+  }
+
   // https://issues.chromium.org/issues/336839115
   assert.throws(() => map.call({ next: null }, () => { /* empty */ }).next(), TypeError);
 });

tests/unit-pure/es.iterator.map.js

@@ -30,6 +30,22 @@ QUnit.test('Iterator#map', assert => {
   const it = createIterator([1], { return() { this.closed = true; } });
   assert.throws(() => map.call(it, {}), TypeError);
   assert.true(it.closed, 'map closes iterator on validation error');
+
+  {
+    let returnCount = 0;
+    const it2 = createIterator([1], {
+      return() {
+        returnCount++;
+        return { done: true, value: undefined };
+      },
+    });
+    const mapped = map.call(it2, x => x);
+    mapped.next();
+    mapped.next(); // exhaust
+    mapped.return();
+    assert.same(returnCount, 0, '.return() on exhausted iterator does not call underlying return');
+  }
+
   // https://issues.chromium.org/issues/336839115
   assert.throws(() => map.call({ next: null }, () => { /* empty */ }).next(), TypeError);
 });