[JSC] %WrapForValidIteratorPrototype%.return should not throw TypeError when underlying iterator's return method is null

sosukesuzuki · sosukesuzuki · commit a9b3c904d0bb · 2025-02-27T22:25:06.000-08:00
https://bugs.webkit.org/show_bug.cgi?id=288714 Reviewed by Yusuke Suzuki. According to the spec[1], `%WrapForValidIteratorPrototype%.return` returns `{ done: true, value: undefined }` if the underlying iterator's `return` method is `null` or `undefined`. However, our JSC throws `TypeError` if the underlying iterator's `return` method is `null`. This patch fixes it to comply with the spec. [1]: https://tc39.es/ecma262/#sec-%wrapforvaliditeratorprototype%.return * JSTests/test262/expectations.yaml: * Source/JavaScriptCore/builtins/WrapForValidIteratorPrototype.js: (return): Canonical link: https://commits.webkit.org/291302@main
diff --git a/JSTests/stress/iterator-from-null-checks.js b/JSTests/stress/iterator-from-null-checks.js
@@ -0,0 +1,15 @@
+function shouldBe(a, b) {
+    if (a !== b)
+        throw new Error(`Expected ${b} but got ${a}`);
+}
+
+const iter = {
+    next() { return { done: false, value: 1 } },
+    return(value) { return { done: true, value } },
+};
+const wrap = Iterator.from(iter);
+
+iter.return = null;
+const returnResult = wrap.return("ignored");
+shouldBe(returnResult.done, true);
+shouldBe(returnResult.value, undefined);
diff --git a/JSTests/test262/expectations.yaml b/JSTests/test262/expectations.yaml
@@ -1332,8 +1332,6 @@ test/staging/sm/Function/function-name-assignment.js:
   default: 'Test262Error: Expected SameValue(«"inParen"», «""») to be true'
 test/staging/sm/Function/function-toString-builtin-name.js:
   default: 'Test262Error: Incorrect match for undefined Expected SameValue(«"fn"», «undefined») to be true'
-test/staging/sm/Iterator/from/modify-return.js:
-  default: 'TypeError: null is not a function'
 test/staging/sm/Iterator/prototype/every/check-fn-after-getting-iterator.js:
   default: 'Test262Error: Actual [get: every, get: return] and expected [get: every] should have the same contents. '
 test/staging/sm/Iterator/prototype/find/check-fn-after-getting-iterator.js:
diff --git a/Source/JavaScriptCore/builtins/WrapForValidIteratorPrototype.js b/Source/JavaScriptCore/builtins/WrapForValidIteratorPrototype.js
@@ -57,7 +57,7 @@ function return()
     var returnMethod = iterator.return;
     // 6. If returnMethod is undefined, then
     //   a. Return CreateIterResultObject(undefined, true).
-    if (returnMethod === @undefined)
+    if (@isUndefinedOrNull(returnMethod))
         return { value: @undefined, done: true };
     // 7. Return ? Call(returnMethod, iterator).
     return returnMethod.@call(iterator);
