class cast exception in ff 17

[Stephen Haberman]

Hey,

I know FF17 is pretty old, but do we care about breakages in it? We
noticed some client-side ClassCastExceptions in our logs that are
from a user on FF17. The app works fine in FF latest.

The exception is odd, because, according to the de-obfuscated stack
trace, given a class hierarchy like:

class Base
class Foo extends Base
class Bar extends Base

We are in "new Foo()", from the Foo cstr we call the Base cstr, which
calls Base.someMethod(). Base.someMethod() calls Base.anotherMethod().

Now the bizarre thing is that we end up in *Bar*.anotherMethod(), and
get a class cast exception.

E.g. somehow we jumped subclasses, and went from executing code in
Foo/Foo's base class to code that is in Bar.

Which seems really odd. Which is why I mention it. If we don't care,
that's fine, but it made me scratch my head for awhile.

(Our production build is using a GWT snapshot from ~April, but I also
reproduced it in our app with a GWT snapshot build from ~last week.)

- Stephen

[Roberto Lublinerman]

Can you isolate the bug and open an issue for it? If you upload a repro case I'll take a look.

- Stephen

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[Goktug Gokdogan]

It might be related to the bug[1] that mdempsky@ filed to Firefox earlier. The Firefox's VM was causing an incorrect polymorphic dispatch sometimes.

[1] https://bugzilla.mozilla.org/show_bug.cgi?id=872796

On Fri, Oct 3, 2014 at 11:52 AM, Stephen Haberman <stephen....@gmail.com> wrote:

- Stephen

[Jens]

I have also seen this behavior once in our app. If I remember correctly the generated JavaScript looked correct, yet FireFox called the wrong method. 

IMHO it is a JIT bug in older Firefox versions.

-- J.

[Stephen Haberman]

> It might be related to the bug[1] that mdempsky@ filed to Firefox
> earlier. The Firefox's VM was causing an incorrect polymorphic
> dispatch sometimes.
>
> [1] https://bugzilla.mozilla.org/show_bug.cgi?id=872796

Ah, nice!

Thanks (Jens too) for saving me the trouble of trying to reproduce
that. I was really not looking forward to it. :-)

- Stephen