Subj : Re: [SpiderMonkey] Error Reporter Failure
To   : Brian Barnes
From : Brendan Eich
Date : Sat Jan 29 2005 11:34 pm

Brian Barnes wrote:
> I seem to be encountering a weird error.  I have an error reporter 
> callback.  Let's say I have two scripts, A and B, loaded into that 
> context.


Scripts are executed on contexts, but not loaded into them -- are you 
thinking of global  objects here?


> Each has one function, funcA in A, and funcB in B.  funcB has 
> a syntax error in it.


That should be caught when the script containing funcB is compiled (or 
evaluated -- evaluate == compile + execute).  Is it?  If not, is it 
really a syntax error?


> If my C code calls funcB, the error report gets called.
> 
> If my C code calls funcA, which has a function that calls back into my C 
> code which in turn calls funcB, the code halts at the error line, fails 
> silently, and NEVER calls the error reporter.
> 
> Case 1 --- Error Reporter gets Called ----
> 
> C code
>      funcB
>          halts at syntax error
>               Error Reporter
> 
> Case 2 -- Error Reporter does not get Called ----
> 
> C code
>      funcA
>          C Code
>               funcB
>                   halts at syntax error
> 
> Has anybody seen this before?  Any idea what might be causing this?


Errors are now exceptions, since ECMA-262 Edition 3 support was added in 
'99 or so.  That means your error reporter won't be called at the point 
where the error-as-exception is thrown.  The engine reports uncaught 
exceptions only when unwinding from the outermost API calll.  It can 
tell that an API is outermost by checking whether there are any 
activations (script executions or function invocations) live on the 
context you're passing in.

So if your code does the right thing by propagating false or null 
failure returns to the outermost "C code" above, the uncaught 
error-as-exception that's thrown at the innermost funcB error point 
*will* be reported.  If you are failing to propagate failure return 
values, fix that bug.  If you're doing something else to "halt at syntax 
error", stop doing that (Dr., it hurts when I do this! ;-) and return 
false if an API fails, to propagate the exception.

/be

.