621119 - Decompilation creates an invalid string literal

Status: RESOLVED FIXED

(Core :: JavaScript Engine, defect)

Description

[Jesse Ruderman]

function f() { "use strict"; return "\u00007" }
print(f);
print(eval(uneval(f)));

typein:4: SyntaxError: octal literals and octal escape sequences are deprecated:
typein:4: function f() {'use strict';return "\07";}
typein:4: ..................................^

The first bad revision is:
changeset:   43f456d9b632
user:        Jim Blandy
date:        Thu Nov 19 09:49:00 2009 -0800
summary:     Bug 514559: Forbid octal literals or escape sequences in strict mode. r=mrbkap

Comment 1

[Jim Blandy :jimb]

(In reply to comment #0)
> function f() { "use strict"; return "\u00007" }
> The first bad revision is:
> changeset:   43f456d9b632
> summary:     Bug 514559: Forbid octal literals or escape sequences in strict
> mode. r=mrbkap

This is the revision that introduced the check that caught the bug, not the revision that introduced the bug. The printer's generated string "\07", is not a valid literal in strict mode code (the rule for "\0" says that it can't be followed by a decimal digit).

Comment 2

[Jim Blandy :jimb]

It should generate "\x00" in that case, I guess.

Comment 3

[Brendan Eich [:brendan]]

Tricky. While "\0" is allowed in strict mode, we have to be careful about what follows being maximum-munched.

Or we could lose the '\0' -> '0' pair in js_EscapeMap.

/be

Comment 4

[Ryan VanderMeulen [:RyanVM]]

js> function f() { "use strict"; return "\u00007" }
js> print(f);
function f() {
    "use strict";
    return "\x007";
}
js> print(eval(uneval(f)));
undefined

Comment 5

[Jeff Walden [:Waldo]]

Comment 4 demonstrates correct behavior.  Recall that eval returns the result of evaluating a Program, not an Expression, and a function statement doesn't affect completion value, so |undefined| gets returned.

This got fixed by bug 430927.

Comment 6

[Jesse Ruderman]

Complete demo of the correct behavior (modulo bug 706305) :

js> function f() { "use strict"; return "\u00007" }
js> print(f);
function f() {
    "use strict";
    return "\x007";
}
js> print(eval( ("(" + uneval(f) + ")" )))
function f() {
    "use strict";
    return "\x007";
}