On Fri, Jul 25, 2014 at 10:15 AM, Jens <[email protected]> wrote:
> Hi,
>
> for some time our app has produced useless stack traces in FF, IE10+11 in
> case of null pointer exceptions thrown by the browser (TypeError: var is
> null). After some debugging I have seen that our app uses CollectorLegacy
> for these browsers because the GWT module had defined <set-property
> name="compiler.useSourceMaps" value="true"> without any condition on the
> user.agent value.
>
>
This is not intended and actually a bug in deferred binding. I'll send a
patch. IE10+ & FF should still be using CollectorModernNoSourceMap.
> After taking a closer look how things work with CollectorLegacy I figured
> that it must always produces useless stack traces for JavaScriptExceptions
> and I am wondering if thats a known fact and if GWT can't handle that any
> better?
>
> Whenever you have a catch block in Java, GWT generates (pseudo code):
>
> catch ($e0) {
> $e0 = wrap($e0);
> if($e0 instanceof Throwable) {
> execute real catch block
> } else {
> throw unwrap($e0);
> }
> }
>
> If $e0 is a javascript exception the wrap() call creates a new GWT
> JavaScriptException and later on when you call getStackTrace() on that
> exception you will see a stack trace whose root is inside the wrap()
> function (exception.fnStack Array) and you won't see any of your own code
> in that stack trace. As an example:
>
> Caused by: java.lang.Throwable: (TypeError) : this.A is null
> at
> com.google.gwt.lang.Exceptions.getCachableJavaScriptException(Exceptions.java:43)
> at com.google.gwt.lang.Exceptions.wrap(Exceptions.java:26)
> *at
> com.google.web.bindery.event.shared.SimpleEventBus.$doFire(SimpleEventBus.java:173)*
> ... 10 more
>
>
> In this case taken from our app above the bold line are missing 6 lines of
> app code that would point to the problem, however CollectorLegacy just
> swallows all of them because of the wrap() code.
>
>
You cannot swallow something that doesn't exist :) For browsers without
stack support (ie8/9, safari5) and without stack emulation enabled, we
don't have any options but crawl and construct the call stack by ourselves
(i.e. CollectorLegacy). We can only do at the time we catch the exception -
in this case EventBus. Unless we generate try/catch blocks to every
statements, that's all we could get from these old browsers - in that case
it just better to enable stack emulation.
> I guess that could be VERY annoying for people supporting IE8+9.
>
>
> Any thoughts?
>
>
> -- J.
>
>
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