Debugger misbehavior in function called via symbol property reference

Version: v4.4.7, v6.2.2
Platform: Windows7 64-bit
Subsystem: debugger

Steps to Reproduce

Create the file test.js with the following code.
Invoke node debug test.js.
The debugger stops at line 1.
Type the command 'c'

var S = Symbol();
var o = {
    [S]() {
        console.log("before");
        debugger;
        console.log("at breakpoint");
        console.log("after");
    }
}
o[S]();

Expected Behavior

"before" is printed then the debugger stops at debugger;.

Actual Behavior

"before" is printed and I get a debug> prompt without any code listing.
If I type 'bt' I get the message 'Can't request backtrace now'.
If I type 'list(5)' I get a list when the current line is marked at line 1.
If I type 'c' then "at breakpoint" and "after" is printed and
the program terminates without ever stopping at the breakpoint.

If I change the last line as follows, everything goes fine.

var S = Symbol();
var o = {
    [S]() {
        console.log("before");
        debugger;
        console.log("at breakpoint");
        console.log("after");
    }
}
var f = o[S];
f();

Node Inspector and VS 2015 Node.js tools also show weird behavior with the sample code. Effectively they are unable to stop at the breakpoint in o[S].

Confirmed. The debugger statement generates a v8::Break debug event without a JSON payload, tricking src/debug-agent.cc into thinking that the debug session has terminated. I'll put together a fix.

Turns out it's (also) a V8 bug. The JSON-ification of the event data fails with a "Cannot convert a Symbol value to a string" exception, that is why the payload is empty.

Filed a CL: https://codereview.chromium.org/2122793003/

@bnoordhuis

@bnoordhuis: Good news. I'm ready to try out the fix as soon as it lands in node.

Handle symbols in FrameMirror#invocationText().

Tracking bug for back-porting the fix to the 5.2 and 5.3 branches: https://bugs.chromium.org/p/v8/issues/detail?id=5191

I'll take care of back-porting it to older branches.

Trying to find a workaround, I ran into a more tricky scenario. It would be nice to see if the proposed fix repairs this one as well.

This piece of code produces the same effect as my original sample. However if the breakpoint is moved into o.g, it works as expected.

var S = Symbol();
var o = {
    [S]() {
        debugger;
        console.log("in o[S]");
    },
    g() {
        console.log("in o.g");
    }
}

var f = o[S];
var g = o.g;

f.call(o);
g.call(o);

One more exotic test case just to make sure that it is covered.

var S = Symbol();
var o = {
    [S]() {
        debugger;
        console.log("in o[S]");
    },
}
var f = o[S].bind(o);
f();

Names are temporarily substituted for symbols

deps: cherry-pick 1f53e42 from v8 upstream

Navigation Menu

Repository navigation

Debugger misbehavior in function called via symbol property reference #7536

Steps to Reproduce

Expected Behavior

Actual Behavior

Metadata

Assignees

Labels

Type

Projects

Milestone

Relationships

Development

Debugger misbehavior in function called via symbol property reference #7536

Description

Steps to Reproduce

Expected Behavior

Actual Behavior

Activity

bnoordhuis commented on Jul 5, 2016

bnoordhuis commented on Jul 5, 2016

bnoordhuis commented on Jul 5, 2016

kkeri commented on Jul 6, 2016

bnoordhuis commented on Jul 8, 2016

kkeri commented on Jul 8, 2016

kkeri commented on Jul 9, 2016

Metadata

Metadata

Assignees

Labels

Type

Projects

Milestone

Relationships

Development

Issue actions