1094995 - for (const ... in/of ...) should work, binding a fresh set of const variables each iteration

Status: RESOLVED WORKSFORME

(Core :: JavaScript Engine, defect)

Description

[Eric Faust [:efaust]]

ziyunfei points out:

> js> const x = undefined;for (x of [1,2,3])print(x);
> typein:2:25 SyntaxError: invalid for/in left-hand side:
> typein:2:25 const x = undefined;for (x of [1,2,3])print(x);
> typein:2:25 .........................^
> js>
> js> const x = undefined;
> js> for (x of [1,2,3])print(x);     // Should this throw an error?
> undefined
> undefined
> undefined

This is crazed. ES6 10/14/14 13.6.4.1 forbids this nonsense.

Comment 1

[Tom S. (please needinfo tschuster)]

This was fixed by bug 1095439. I am however going to re-purpose this bug to add this testcase and change for (const x .. ) to a SyntaxError.

Comment 2

[Tom S. (please needinfo tschuster)]

Apparently they decided to make this a runtime error, again?!

Comment 3

[Turadg Aleahmad]

`for (const x ...)` is valid, not a syntax error.

See test ES6 spec test case https://github.com/tc39/test262/blob/1c1a75eead413ab5152e825d3c551908667e405f/test/language/statements/for-in/const-fresh-binding-per-iteration-for-in.js#L10

Comment 4

[Jeff Walden [:Waldo]]

Once I've fixed bug 449811 and/or bug 1069480 and/or some other bug in a massive bug-confluence that I intend to fix approximately all at once, this should be a few-line change in the parser, only.  That work is In Progress as we speak.

Comment 6

[Jeff Walden [:Waldo]]

This got fixed in the parser rewrite, don't remember what bug number to use for dup/dependency, not important.