Ok I’ve finished the implementation and will be committing soon.
Note that this could change slightly what the user sees.
For example in the past if you had this velocity script:
{{velocity}}
$someclass.someMethodThrowingException()
… rest of the script here...
{{/velocity}}
The user would see a stack trace on his screen before upgrading to 8.0 and
after upgrading to 8.0 he’ll see something different which depends on what the
“… rest of the script here…” does.
What I don’t like too much is that this could lead to unwanted side effects.
For example, imagine that we have the following:
{{velocity}}
#set ($docReference =
$someclass.someMethodComputingTheReferenceButThrowingException())
…
$xwiki.getDocument($docReference).save()
...
{{/velocity}}
Then if an exception is raised in
someMethodComputingTheReferenceButThrowingException() it used to display an
exception but will now do something else. It happens that in this case it’ll
report a NPE (AFAICS in the code) but we could imagine it would create a wrong
document in the wiki, etc.
Any thoughts about this? Should I still go ahead (I think so).
Thanks
-Vincent
On 15 Jan 2016 at 13:37:39, vinc...@massol.net
(vinc...@massol.net(mailto:vinc...@massol.net)) wrote:
>
>
>
>
>
> On 15 Jan 2016 at 13:26:08, vinc...@massol.net
> (vinc...@massol.net(mailto:vinc...@massol.net)) wrote:
>
> >
> > On 15 Jan 2016 at 13:23:07, vinc...@massol.net
> > (vinc...@massol.net(mailto:vinc...@massol.net)) wrote:
> >
> > > Forget what I’ve said regarding the #try directive.
> > >
> > > Actually the way to use it is:
> > >
> > > #try()
> > > … wrap some script snipper, one or several calls…
> > > #end
> > > .. here only you can access the $exception binding.
> > >
> > > Thus:
> > >
> > > * Wrapping the whole content to evaluate won’t work
> > > * The Exception Catching Uberspector is really what we need. It’s more
> > > fine-grained than the #try directive (or it’s equivalent if you use
> > > #try() for each line of script calling methods).
> > >
> > > In addition:
> > >
> > > * We provide script APIs in xwiki-commons too so if we want this best
> > > practice of throwing exceptions in script APIs, we also need to make this
> > > work in xwiki-commons when used outside of XWiki. Thus we need a solution
> > > there too.
> > > ** A) One solution would be to use XWiki’s Context and make the last
> > > exception available with $xcontext.lastVelocityException but it’s not
> > > very natural, I hope we can find a better solution
> > > ** B) Another solution is to move VelocityManager to commons in
> > > xwiki-commons-velocity, offer a basic impl without skin support and
> > > override it in xwiki-platform to add the platform-specific stuff.
> > >
> > > I’ll start exploring B). Let me know if you don’t agree or if you have a
> > > better idea.
> >
> > Actually VelocityManager is already in commons, it’s the impl that is in
> > platform. So right now it will work for us; it just won’t work for users
> > who use just commons. Like if you use the Rendering in standalone mode.
>
> Actually forget that, I don’t need to use VelocityManager in practice (and it
> would be costly to do so). I just need to use the Execution component:
>
> VelocityContext vcontext =
> (VelocityContext) this.execution.getContext().getProperty(
> VelocityExecutionContextInitializer.VELOCITY_CONTEXT_ID);
>
>
> Thanks
> -Vincent
>
> Ps: Sorry for the live design noise...
>
> >
> > Thanks
> > -Vincent
> >
> > > Thanks
> > > -Vincent
> > >
> > >
> > > On 15 Jan 2016 at 12:15:41, vinc...@massol.net
> > > (vinc...@massol.net(mailto:vinc...@massol.net)) wrote:
> > >
> > > >
> > > > [snip]
> > > >
> > > > > > > > > >> > Hi devs,
> > > > > > > > > >> >
> > > > > > > > > >> > Right now our strategy is for script services and script
> > > > > > > > > >> > APIs in general
> > > > > > > > > >> > to catch exceptions, store them and offer a
> > > > > > > > > >> > getLastError() method to get
> > > > > > > > > >> > them (see
> > > > > > > > > >> > http://extensions.xwiki.org/xwiki/bin/view/Extension/Script+Module#HBestPractices
> > > > > > > > > >> > )
> > > > > > > > > >> >
> > > > > > > > > >> > However it would be much nicer to:
> > > > > > > > > >> > * Let our script services generate exceptions
> > > > > > > > > >> > * Offer a velocity script service to get the last
> > > > > > > > > >> > exception raised by a
> > > > > > > > > >> > java call from velocity
> > > > > > > > > >> > * Implement this uberspector to catch the exceptions and
> > > > > > > > > >> > to set them in
> > > > > > > > > >> > the execution context
> > > > > > > > > >> >
> > > > > > > > > >> > That should be quite easy to implement IMO.
> > > > > > > > > >> >
> > > > > > > > > >> > WDYT?
> > > > > > > > > >> >
> > > > > > > > > >>
> > > > > > > > > >> +1, it's a pain to call setLastError() everywhere there
> > > > > > > > > >> can be an exception
> > > > > > > > > >> thrown, and we almost always forget to do it (for this
> > > > > > > > > >> reason).
> > > > > > > > > >>
> > > > > > > > > >> Note that we also have the #try() directive now.
> > > > > > > > > >
> > > > > > > > > > Yes, I should have mentioned that there’s indeed also this
> > > > > > > > > > possibility:
> > > > > > > > > > * Have script API throw Exceptions
> > > > > > > > > > * Force velocity script users to wrap their code with the
> > > > > > > > > > try directive when they need to catch exceptions
> > > > > > > > > >
> > > > > > > > > > I still believe that the use of the Exception-catching
> > > > > > > > > > uberspector is better.
> > > > > > > > > >
> > > > > > > > > > WDYT?
> > > > > > > > >
> > > > > > > > > Does it mean you plan to get rid of new #try directive ?
> > > > > > > > > Because it
> > > > > > > > > will be broken with this new uberspector.
> > > > > > > >
> > > > > > > > That’s a good point, I had not thought about the implementation
> > > > > > > > at this stage.
> > > > > > > >
> > > > > > > > I think this could still work. When the #try directive is used
> > > > > > > > I’d just have to setup some flag somewhere in Velocity and in
> > > > > > > > the uberspector I could check if this flag is set and if so
> > > > > > > > then don’t catch the exception.
> > > > > > >
> > > > > > >
> > > > > > > Actually, thinking more, I think you’re right and that the #try
> > > > > > > directive plays exactly the same role as an Exception-catching
> > > > > > > uberspector and I don’t see the need for the #try directive if we
> > > > > > > provide an uberspector.
> > > > > > >
> > > > > > > So I’m proposing to deprecate it but still keep it for backward
> > > > > > > compatibility for now (probably a full cycle).
> > > > > > >
> > > > > > > WDYT?
> > > > > >
> > > > > > Note that I’d like to change a bit the proposal and instead of
> > > > > > making the exception available from a script service, I’d prefer to
> > > > > > make it available as a known velocity binding such as
> > > > > > $lastException. There’s no reason to use a script service since
> > > > > > that would mean it would work for all scripts and in this case we
> > > > > > only want it to work for Velocity.
> > > > > >
> > > > > > Since there’s no way to get the Velocity Context from within an
> > > > > > uberspector, I’ll get it by using our Component Manager and get the
> > > > > > VelocityManager component and call getVelocityContext()… If you
> > > > > > know a better way, let me know.
> > > > >
> > > > > hmm… this would mean that I’d need to put this new uberspector in
> > > > > xwiki-platform since VelocityManager is in platform ATM… (@Thomas:
> > > > > our discussion of yesterday ;)).
> > > >
> > > >
> > > > There’s an alternative, which is to modify our implementation of
> > > > VelocityEngine.evaluate() and decorate the source with a #try()
> > > > directive so that it’s always called (and make sure that calling it
> > > > nested won’t affect it for backward compat).
> > > >
> > > > This could be simpler to implement and doesn’t force us to move some
> > > > velocity code to platform.
> > > >
> > > > WDYT?
> > > >
> > > > Thanks
> > > > -Vincent
> > > >
> > > > [snip]
> >
> > _______________________________________________
> > devs mailing list
> > devs@xwiki.org
> > http://lists.xwiki.org/mailman/listinfo/devs
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