1338796 - IteratorClose shouldn't be called in yield* when resuming generator with Throw completion and throw method is present

Status: RESOLVED FIXED

(Core :: JavaScript Engine, defect)

Description

[André Bargull [:anba]]

Test case:
---
var iterable = {
    [Symbol.iterator]() {
        return {
            next(x) {
                print("NEXT called");
                return { done: false };
            },
            return(x) {
                print("RETURN called");
                return { done: true };
            },
            throw(e) {
                print("THROW called");
                throw e;
            },
        };
    }
};

function* y() {
    yield* iterable;
}

var g1 = y();
g1.next();
try { g1.throw(); } catch (e) { }
---

Expected: Prints "NEXT called" and then "THROW called", but doesn't print "RETURN called"
Actual: Also prints "RETURN called"

Test case is derived from ecma_6/Generators/yield-star-iterator-close.js

Comment 1

[Shu-yu Guo [:shu]]

Attachment: Do not call iterator.return if iterator.throw is present in yield*.

I refactored the iterator.return() code due to yield* out of emitIteratorClose,
because the semantics are fairly different. This lets emitIteratorClose to be
easier to read and be 1:1 with the spec text.

Comment 2

[Tooru Fujisawa [:arai]]

Comment on attachment 8836975 [details] [diff] [review]
Do not call iterator.return if iterator.throw is present in yield*.

Review of attachment 8836975 [details] [diff] [review]:
-----------------------------------------------------------------

yeah, now it's easy to follow the execution, nice :)

::: js/src/frontend/BytecodeEmitter.cpp
@@ +8306,5 @@
> +    // Step v.
> +    if (!emitCheckIsObj(CheckIsObjectKind::IteratorReturn)) // ITER OLDRESULT FTYPE FVALUE RESULT
> +        return false;
> +
> +    // Step vi-viii.

Steps

Comment 3

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/mozilla-inbound/rev/697c73202fb6
Do not call iterator.return if iterator.throw is present in yield*. (r=arai)

Comment 4

[Carsten Book [:Tomcat]]

https://hg.mozilla.org/mozilla-central/rev/697c73202fb6

Comment 5

[Ryan VanderMeulen [:RyanVM]]

https://hg.mozilla.org/releases/mozilla-beta/rev/f3a27a0d9884