[Webkit-unassigned] [Bug 215877] [GLIB] No way to determine if an exception has been thrown calling jsc_value_object_invoke_methodv

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=215877

--- Comment #5 from Michael Gratton <mike at vee.net> ---
(In reply to Carlos Garcia Campos from comment #4)
> (In reply to Michael Gratton from comment #2)
> > So I've just found `jsc_context_get_exception` and
> > `jsc_context_clear_exception`, which helps (just)! There are some problems
> > with this however:
> > 
> >  1. It is racy between invocations
> 
> What's racy?

1. Call jsc_value_object_invoke_methodv in an async or threaded context
3. Call jsc_value_object_invoke_methodv in a different async/threaded context
4. return to the call from (1)
5. call jsc_context_get_exception

If non-null, which call does the exception apply to?

If the answer here is always "call `jsc_context_get_exception` immediately after invoking a JS callable so the exception isn't overwritten" then it would be nice if the API did that automatically so that people that use the API don't have to know or remember to do so.

If the answer is "This isn't possible" then that's not documented (either).

> >  2. There's no documentation about when it's valid to call either method, if
> > the latter needs to be called and if so, when
> 
> You can check if there's an exception being raised in the context, and you
> can clear ii to "handle" it, if it's not fatal, to ensure new exceptions are
> thrown.

Great, but that's not documented, hence this bug.

> 
> >  3. There is no documentation to suggest this is actually useful for the use
> > case above
> 
> What use case exactly?

Determining if an exception has been called after calling `jsc_value_object_invoke_methodv` (or some other way to invoke a JS callable). I only found it much later because I was looking at something else.

> >  4. No members are ever set when this object is non-null due to an exception
> > being thrown after call to `jsc_value_object_invoke_methodv` - name,
> > source-uri, etc are always null, line and column numbers are always 0
> > (they're not even -1, since these are uints)
> 
> What's the script name and row/column of a method called by
> jsc_value_object_invoke_methodv?

In the case of an exception being raised by a method called by `jsc_value_object_invoke_methodv` that is defined in a JavaScript source file, the script name is the name of the source file and the row/column is the line number and column number of the throw statement, presumably?

> > So aside from the fixes needed for (2)-(4), consider this a feature request
> > for an API that doesn't have the limitations of (1). Thanks!
> 
> I don't understand the limitations, could you elaborate? Maybe a test case
> would help me to understand the issue.

These are all issues of API documentation and ergonomics, so I guess I am the test case. :) More specifically, I've been porting Geary to use the UserMessage API and have been reporting bugs for things that are missing based on that experience.

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