Debug scope proxies don't let eval-in-frame code define new properties

RESOLVED FIXED in mozilla15



JavaScript Engine
5 years ago
5 years ago


(Reporter: Honza, Assigned: luke)


Windows Vista

Firefox Tracking Flags

(Not tracked)



(1 attachment)



5 years ago
Firebug's test doesn't work since the "TypeError: can't redefine non-configurable property" error appears when evaluating the following script in a frame:

if (!window._firebug)window._firebug={};
window._firebug.rerunThis = this;
window._firebug.rerunArgs = [];
if (arguments && arguments.length) for (var i = 0; i < arguments.length; i++) window._firebug.rerunArgs.push(arguments[i]);
window._firebug.rerunFunctionName = onclick;
window._firebug.rerunFunction = function _firebugRerun() { onclick.apply(window._firebug.rerunThis, window._firebug.rerunArgs); }

See the source here:

1) Install Firebug:
2) Load:
3) Follow the steps on the page -> after clicking re-run, the debugger doesn't halt again -> BUG

You can also see the error by installing FBTrace:

Open FBTrace by "Firebug (icon) menu -> Open Firebug Tracing". In the console check UI_LOOP option (within the Options tab) and watch the console when pressing the rerun button during the test case.

The log comes from this source location:

The log:
debugger.rerun false and result: [object Object] for http://legoas/src/

- Expand the log
- Select the Object tab
- Result -> Value -> stringValue == "TypeError: can't redefine non-configurable property 'i'"

It works in Firefox 13

Is there something wrong with the evaluated script?


Comment 1

5 years ago
That error pops out when eval-in-frame code tries to redefine a binding in the enclosing scope.  Right now, the error is overly conservative (it throws on *any* call to defineProperty on the scope object) since it wasn't even clear how this path would be exercised (normal reads/writes go through get/set).  I'll look at what your test-case is doing and probably we can relax the restriction to allow defineProperty when, e.g., only the value changes.


5 years ago
Summary: TypeError: can't redefine non-configurable property → Debug scope proxies don't let eval-in-frame code define new properties

Comment 2

5 years ago
Created attachment 628845 [details] [diff] [review]
fix and tests

Simple enough fix; thanks for the great STR!  With this patch, do you see any other problems Jan?

The eif-call-newvar change is just reverting the change made in bug 690135.
Assignee: general → luke
Attachment #628845 - Flags: review?(jimb)

Comment 3

5 years ago
Comment on attachment 628845 [details] [diff] [review]
fix and tests

Review of attachment 628845 [details] [diff] [review]:

Looks good to me. Would it be worthwhile to test that a *re*declaration of a variable also works?
Attachment #628845 - Flags: review?(jimb) → review+

Comment 4

5 years ago
(In reply to Jim Blandy :jimb from comment #3)
Heh, well, that actually doesn't work with the patch (that's what the if(has) Throw is guarding against).  To make it work, we'd need to do a lot more thinking to make sure the PropertyDescriptors match and then the soon-to-be-landed patches in bug 659577 would need to do the right thing for unaliased variables.  All in all, I'd rather not do it if it isn't necessary.

Comment 5

5 years ago
As jimb pointed out on irc, re-defining a var does not call defineProperty, but just sets the existing var, so it should work just fine.  Pushed with the suggested redefinition test:
Target Milestone: --- → mozilla15
Last Resolved: 5 years ago
Resolution: --- → FIXED

Comment 7

5 years ago
(In reply to Luke Wagner [:luke] from comment #2)
> Simple enough fix; thanks for the great STR!  With this patch, do you see
> any other problems Jan?
It looks like this will be in Nightly soon so, I'll let you know.

Thanks for the quick fix!


Comment 8

5 years ago
Retested with today's Nightly and STR from comment #0 works for me

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