462385 - Strange scoping with "for each (let ... in ...)"

Status: RESOLVED FIXED

(Core :: JavaScript Engine, defect)

Description

[Jesse Ruderman]

js> x = 3; for each (let x in [x]) { print(x) } 
undefined

I think it should print 3.

Comment 1

[Jeff Walden [:Waldo]]

Dup of bug 344952?  Is the let here semantically equivalent to a let ... statement (what I assume) or to a let (...) ... statement?  mrbkap?

Comment 2

[Brendan Eich [:brendan]]

No, this is a real bug. In the for-in loop and variants, the scope of a let in the LHS if in should not open over the RHS evaluation, only over the body. In a C-style for(let x=...;...;...) loop the scope should open over the condition and update parts only, not the initializer for x.

Blake, you game to take this?

/be

Comment 3

[nanto_vi (TOYAMA Nao)]

var o = { x: "out of let" };
let (o = { y: function () { return o.x; }, x: "rhs of let" }) alert(o.y());

This outputs "rhs of let".  Is this behavior the same bug as this bug or should I file a new bug?

Comment 4

[Brendan Eich [:brendan]]

(In reply to comment #3)
> var o = { x: "out of let" };
> let (o = { y: function () { return o.x; }, x: "rhs of let" }) alert(o.y());
> 
> This outputs "rhs of let".  Is this behavior the same bug as this bug or should
> I file a new bug?

Indeed this bug is fixed, probably by upvar2, in my tm build, also in m-c and (I bet) in 1.9.1:

js> x = 3; for each (let x in [x]) { print(x) } 
3

So please file comment 3 as a new bug. Thanks,

/be

Comment 5

[nanto_vi (TOYAMA Nao)]

I filed bug 500909 for comment 3.