462309 - Decompilation is not accepted, involving "let" and serial evaluation comma

Status: RESOLVED WORKSFORME

(Core :: JavaScript Engine, defect)

Description

[Jesse Ruderman]

js> f = (function() { (let (y) y, y) })
function () {
    let (y) y, y;
}
js> eval(uneval(f))
typein:2: SyntaxError: missing ; before statement:
typein:2: (function () {let (y) y, y;})
typein:2: ......................^

Dunno which step is wrong.

Comment 1

[Brendan Eich [:brendan]]

mrbkap: do you remember why 'let (head) expr' at the start of a statement must be parenthesized if it is an operand in a comma expression? The expr is supposed to be an assignment expression, which is what comma expression produces.

/be

Comment 2

[Blake Kaplan (:mrbkap) (inactive)]

Well, we call AssignExpr, but that doesn't include the comma operator. Expr does. Are the functions misnamed?

Comment 3

[Brendan Eich [:brendan]]

(In reply to comment #2)
> Well, we call AssignExpr, but that doesn't include the comma operator. Expr
> does. Are the functions misnamed?

Not really: Expr is the goal symbol for the expression sub-grammar, and we want let expression bodies to be assignment expressions. The problem is that we do not keep parsing after the let expression on the left of comma. This reminds me of the bug Waldemar pointed out:

let (a = 1) a ? f : x++();

x++() is not valid syntax by itself, but a bottom-up parser would recognize the (let (a = 1) a ? f : x++) as the callee.

/be

Comment 4

[Blake Kaplan (:mrbkap) (inactive)]

Oops. This is a two year old bug.

Comment 5

[Ryan VanderMeulen [:RyanVM]]

(In reply to Blake Kaplan (:mrbkap) from comment #4)
> Oops. This is a two year old bug.

Make that five ;)

Comment 6

[Blake Kaplan (:mrbkap) (inactive)]

IIRC this is a conflict in the "grammar" (quotes because no such thing existed when I implemented this). I don't remember the details any more, though. dherman might know more, though!

Comment 7

[Luke Wagner [:luke]]

Fixed by saving the source.