1141255 - The debugger can modify unaliased consts

Status: RESOLVED FIXED

(Core :: JavaScript Engine, defect)

Description

[Jan de Mooij [:jandem]]

We fail the testcase below because setVariable sets the const's value to 3.

However, if the const is aliased (just add a debugger-statement or a lambda that uses 'x'), the debugger is no longer able to modify it and it throws TypeError: "x" is read-only.

var g = newGlobal();
g.parent = this;
g.eval("(" + function() {
    var dbg = new Debugger(parent);
    dbg.onEnterFrame = function(frame) {
	frame.onStep = function() {
	    if (frame.environment.getVariable("x") === 2)
		frame.environment.setVariable("x", 3);
	}
    };
} + ")()");
function f() {
    const x = 2;
    assertEq(x, 2);
}
f();

Comment 1

[Tom S. (please needinfo tschuster)]

Is this maybe fixed by the frontend rewrite?

Comment 2

[Tom S. (please needinfo tschuster)]

Apparently not :/
> Assertion failed: got 3, expected 2

Comment 3

[Shu-yu Guo [:shu]]

This should be consistent, either both frame and env bindings can be modified or neither can be. But I'm still unclear if this should be allowed or disallowed. I'll chat with jimb.

Comment 4

[André Bargull [:anba]]

Attachment: Bug 1141255: Prevent debugger from modifying unaliased const bindings. r=jandem!

Comment 5

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/9c7cd2409020
Prevent debugger from modifying unaliased const bindings. r=jandem

Comment 6

[Norisz Fay [:noriszfay]]

https://hg.mozilla.org/mozilla-central/rev/9c7cd2409020