Add coverage for some implementation bugs in Iterator helper methods

test/built-ins/Iterator/prototype/drop/next-method-called-with-zero-arguments.js

@@ -0,0 +1,47 @@
+// Copyright (C) 2025 André Bargull. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-iteratorprototype.drop
+description: >
+  Underlying iterator's next method is called with zero arguments.
+info: |
+  27.1.4.2 Iterator.prototype.drop ( limit )
+
+  ...
+  10. Let closure be a new Abstract Closure with no parameters that captures
+      iterated and integerLimit and performs the following steps when called:
+    ...
+    b. Repeat, while remaining > 0,
+      ...
+      ii. Let next be ? IteratorStep(iterated).
+      ...
+    c. Repeat,
+      i. Let value be ? IteratorStepValue(iterated).
+      ...
+  ...
+features: [iterator-helpers]
+---*/
+
+var counter = 0;
+
+var underlying = {
+  next() {
+    assert.sameValue(arguments.length, 0);
+
+    return {
+      done: false,
+      value: ++counter,
+    };
+  }
+};
+
+var it = Iterator.prototype.drop.call(underlying, 3);
+
+assert.sameValue(counter, 0);
+
+assert.sameValue(it.next().value, 4);
+assert.sameValue(it.next(1).value, 5);
+assert.sameValue(it.next(1, 2).value, 6);
+
+assert.sameValue(counter, 6);

test/built-ins/Iterator/prototype/drop/return-method-called-with-zero-arguments.js

@@ -0,0 +1,100 @@
+// Copyright (C) 2024 André Bargull. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-iteratorprototype.drop
+description: >
+  Underlying iterator's return method is called with zero arguments.
+info: |
+  27.1.4.2 Iterator.prototype.drop ( limit )
+
+  ...
+  10. Let closure be a new Abstract Closure with no parameters that captures
+      iterated and integerLimit and performs the following steps when called:
+    ...
+    c. Repeat,
+      ...
+      iii. Let completion be Completion(Yield(value)).
+      iv. IfAbruptCloseIterator(completion, iterated).
+  ...
+
+  27.1.2.1.2 %IteratorHelperPrototype%.return ( )
+    ...
+    4. If O.[[GeneratorState]] is suspended-start, then
+      ...
+      c. Perform ? IteratorClose(O.[[UnderlyingIterator]], NormalCompletion(unused)).
+      ...
+    5. Let C be ReturnCompletion(undefined).
+    6. Return ? GeneratorResumeAbrupt(O, C, "Iterator Helper").
+features: [iterator-helpers]
+---*/
+
+var counter = 0;
+
+var underlying = {
+  next() {
+    return {
+      done: false,
+      value: 0,
+    };
+  },
+  return() {
+    assert.sameValue(arguments.length, 0);
+
+    counter += 1;
+    return {};
+  }
+};
+
+// Close from "suspended-start".
+{
+  var it = Iterator.prototype.drop.call(underlying, 0);
+
+  assert.sameValue(counter, 0);
+  it.return();
+  assert.sameValue(counter, 1);
+}
+
+{
+  var it = Iterator.prototype.drop.call(underlying, 0);
+
+  assert.sameValue(counter, 1);
+  it.return(1);
+  assert.sameValue(counter, 2);
+}
+
+{
+  var it = Iterator.prototype.drop.call(underlying, 0);
+
+  assert.sameValue(counter, 2);
+  it.return(1, 2);
+  assert.sameValue(counter, 3);
+}
+
+// Close from "suspended-yield".
+{
+  var it = Iterator.prototype.drop.call(underlying, 0);
+  it.next();
+
+  assert.sameValue(counter, 3);
+  it.return();
+  assert.sameValue(counter, 4);
+}
+
+{
+  var it = Iterator.prototype.drop.call(underlying, 0);
+  it.next();
+
+  assert.sameValue(counter, 4);
+  it.return(1);
+  assert.sameValue(counter, 5);
+}
+
+{
+  var it = Iterator.prototype.drop.call(underlying, 0);
+  it.next();
+
+  assert.sameValue(counter, 5);
+  it.return(1, 2);
+  assert.sameValue(counter, 6);
+}

test/built-ins/Iterator/prototype/drop/suspended-start-iterator-close-calls-next.js

@@ -0,0 +1,72 @@
+// Copyright (C) 2025 André Bargull. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iterator.prototype.drop
+description: >
+  Generator is closed from suspended-start state and IteratorClose calls next.
+info: |
+  27.1.2.1.2 %IteratorHelperPrototype%.return ( )
+    ...
+    4. If O.[[GeneratorState]] is suspended-start, then
+       a. Set O.[[GeneratorState]] to completed.
+       ...
+       c. Perform ? IteratorClose(O.[[UnderlyingIterator]], NormalCompletion(unused)).
+       d. Return CreateIteratorResultObject(undefined, true).
+    ...
+
+  7.4.11 IteratorClose ( iteratorRecord, completion )
+    ...
+    3. Let innerResult be Completion(GetMethod(iterator, "return")).
+    4. If innerResult is a normal completion, then
+       a. Let return be innerResult.[[Value]].
+       b. If return is undefined, return ? completion.
+       c. Set innerResult to Completion(Call(return, iterator)).
+    ...
+
+  27.1.2.1.1 %IteratorHelperPrototype%.next ( )
+    1. Return ? GeneratorResume(this value, undefined, "Iterator Helper").
+
+  27.5.3.3 GeneratorResume ( generator, value, generatorBrand )
+    1. Let state be ? GeneratorValidate(generator, generatorBrand).
+    2. If state is completed, return CreateIteratorResultObject(undefined, true).
+    ...
+
+  27.5.3.2 GeneratorValidate ( generator, generatorBrand )
+    ...
+    5. Let state be generator.[[GeneratorState]].
+    6. If state is executing, throw a TypeError exception.
+    7. Return state.
+features: [iterator-helpers]
+---*/
+
+var returnCallCount = 0;
+
+var underlying = {
+  next() {
+    throw new Test262Error("Unexpected call to next");
+  },
+  return() {
+    returnCallCount += 1;
+
+    // The generator state is already set to "completed". The generator state is
+    // not "executing", so `GeneratorValidate` succeeds and `GeneratorResume`
+    // returns with `CreateIteratorResultObject()`.
+    var result = it.next();
+    assert.sameValue(result.value, undefined);
+    assert.sameValue(result.done, true);
+
+    return {};
+  },
+};
+
+var it = Iterator.prototype.drop.call(underlying, 0);
+
+assert.sameValue(returnCallCount, 0);
+
+// This `return()` call sets the generator state to "completed" and then calls
+// `IteratorClose()`.
+var result = it.return();
+assert.sameValue(result.value, undefined);
+assert.sameValue(result.done, true);
+
+assert.sameValue(returnCallCount, 1);

test/built-ins/Iterator/prototype/drop/suspended-start-iterator-close-calls-return.js

@@ -0,0 +1,76 @@
+// Copyright (C) 2025 André Bargull. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iterator.prototype.drop
+description: >
+  Generator is closed from suspended-start state and IteratorClose calls return.
+info: |
+  27.1.2.1.2 %IteratorHelperPrototype%.return ( )
+    ...
+    4. If O.[[GeneratorState]] is suspended-start, then
+       a. Set O.[[GeneratorState]] to completed.
+       ...
+       c. Perform ? IteratorClose(O.[[UnderlyingIterator]], NormalCompletion(unused)).
+       d. Return CreateIteratorResultObject(undefined, true).
+    5. Let C be ReturnCompletion(undefined).
+    6. Return ? GeneratorResumeAbrupt(O, C, "Iterator Helper").
+
+  7.4.11 IteratorClose ( iteratorRecord, completion )
+    ...
+    3. Let innerResult be Completion(GetMethod(iterator, "return")).
+    4. If innerResult is a normal completion, then
+       a. Let return be innerResult.[[Value]].
+       b. If return is undefined, return ? completion.
+       c. Set innerResult to Completion(Call(return, iterator)).
+    ...
+    8. Return ? completion.
+
+  27.5.3.4 GeneratorResumeAbrupt ( generator, abruptCompletion, generatorBrand )
+    1. Let state be ? GeneratorValidate(generator, generatorBrand).
+    2. If state is suspended-start, then
+      ...
+    3. If state is completed, then
+      a. If abruptCompletion is a return completion, then
+        i. Return CreateIteratorResultObject(abruptCompletion.[[Value]], true).
+      ...
+
+  27.5.3.2 GeneratorValidate ( generator, generatorBrand )
+    ...
+    5. Let state be generator.[[GeneratorState]].
+    6. If state is executing, throw a TypeError exception.
+    7. Return state.
+features: [iterator-helpers]
+---*/
+
+var returnCallCount = 0;
+
+var underlying = {
+  next() {
+    throw new Test262Error("Unexpected call to next");
+  },
+  return() {
+    returnCallCount += 1;
+
+    // The generator state is already set to "completed", so this `return()`
+    // call proceeds to `GeneratorResumeAbrupt`. The generator state is not
+    // "executing", so `GeneratorValidate` succeeds and `GeneratorResumeAbrupt`
+    // returns with `CreateIteratorResultObject()`.
+    var result = it.return();
+    assert.sameValue(result.value, undefined);
+    assert.sameValue(result.done, true);
+
+    return {};
+  },
+};
+
+var it = Iterator.prototype.drop.call(underlying, 0);
+
+assert.sameValue(returnCallCount, 0);
+
+// This `return()` call sets the generator state to "completed" and then calls
+// `IteratorClose()`.
+var result = it.return();
+assert.sameValue(result.value, undefined);
+assert.sameValue(result.done, true);
+
+assert.sameValue(returnCallCount, 1);

test/built-ins/Iterator/prototype/drop/suspended-yield-iterator-close-calls-next.js

@@ -0,0 +1,98 @@
+// Copyright (C) 2025 André Bargull. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iterator.prototype.drop
+description: >
+  Generator is closed from suspended-yield state and IteratorClose calls next.
+info: |
+  27.1.2.1.2 %IteratorHelperPrototype%.return ( )
+    ...
+    5. Let C be ReturnCompletion(undefined).
+    6. Return ? GeneratorResumeAbrupt(O, C, "Iterator Helper").
+
+  27.5.3.4 GeneratorResumeAbrupt ( generator, abruptCompletion, generatorBrand )
+    1. Let state be ? GeneratorValidate(generator, generatorBrand).
+    ...
+    4. Assert: state is suspended-yield.
+    ...
+    8. Set generator.[[GeneratorState]] to executing.
+    ...
+    10. Resume the suspended evaluation of genContext using abruptCompletion as
+        the result of the operation that suspended it. Let result be the
+        Completion Record returned by the resumed computation.
+    ...
+
+  27.5.3.2 GeneratorValidate ( generator, generatorBrand )
+    ...
+    5. Let state be generator.[[GeneratorState]].
+    6. If state is executing, throw a TypeError exception.
+    7. Return state.
+
+  27.1.4.2 Iterator.prototype.drop ( limit )
+    ...
+    10. Let closure be a new Abstract Closure with no parameters that captures
+        iterated and integerLimit and performs the following steps when called:
+      ...
+      c. Repeat,
+        ...
+        iii. Let completion be Completion(Yield(value)).
+        iv. IfAbruptCloseIterator(completion, iterated).
+    ...
+
+  7.4.12 IfAbruptCloseIterator ( value, iteratorRecord )
+    ...
+    2. If value is an abrupt completion, return ? IteratorClose(iteratorRecord, value).
+    ...
+
+  7.4.11 IteratorClose ( iteratorRecord, completion )
+    ...
+    3. Let innerResult be Completion(GetMethod(iterator, "return")).
+    4. If innerResult is a normal completion, then
+       a. Let return be innerResult.[[Value]].
+       b. If return is undefined, return ? completion.
+       c. Set innerResult to Completion(Call(return, iterator)).
+    ...
+
+  27.1.2.1.1 %IteratorHelperPrototype%.next ( )
+    1. Return ? GeneratorResume(this value, undefined, "Iterator Helper").
+
+  27.5.3.3 GeneratorResume ( generator, value, generatorBrand )
+    1. Let state be ? GeneratorValidate(generator, generatorBrand).
+    ...
+features: [iterator-helpers]
+---*/
+
+var returnCallCount = 0;
+
+var underlying = {
+  next() {
+    return {value: 123, done: false};
+  },
+  return() {
+    returnCallCount += 1;
+
+    // The generator state is set to "executing", so this `next()` call throws
+    // a TypeError when `GeneratorResume` performs `GeneratorValidate`.
+    assert.throws(TypeError, function() {
+      it.next();
+    });
+
+    return {};
+  },
+};
+
+var it = Iterator.prototype.drop.call(underlying, 0);
+
+// Move generator into "suspended-yield" state.
+var result = it.next();
+assert.sameValue(result.value, 123);
+assert.sameValue(result.done, false);
+
+assert.sameValue(returnCallCount, 0);
+
+// This `return()` call continues execution in the suspended generator.
+var result = it.return();
+assert.sameValue(result.value, undefined);
+assert.sameValue(result.done, true);
+
+assert.sameValue(returnCallCount, 1);