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Re: [wtp-dev] Nashorn Debugging 
On 17 Mar 2015, at 12:16, Harald Wellmann wrote:
Yes, that's just the stuff I'd found out for so far (i.e. DebuggerSupport 
according to JDK-8044798), see my first message. I've also looked at
NetBeans sources to get an understanding of how to gather of script source 
line info by tracking ClassPrepare events for
jdk.nashorn.internal.scripts.Script* classes. That looks like the easier 
part of the story.


cool.
The harder part (at least for me) is how to fit this into the JDT and JSDT design. (I'm familiar with Eclipse plugin development in general, but not 
really with J(S)DT details.)
I'm also learning in this area - might need to try grab a JDT guy to help ;)
So far, I've created an alternative NashornLaunchDelegate for the standard Java debug launcher to create extra breakpoints for DebuggerSupport and Script* classes in the JDIDebugTarget. This should eventually let me step from Java into JavaScript code invoked from a plain old Java application 
via ScriptEngine.
sounds cool - so just to verify I grok it right - does this require user launch the debugger as a "nashorn launch" or will it work on any Java launched app that debugger gets 
connected to.


(Directly launching a *.js source like jjs does would be
a different story, which I'm not considering for now.)


yeah thats different.


There were two issues:
- JavaClassPrepareBreakpoint does not handle wildcards in class names. I 
had to extend this class.


because nashorn generates wildcars into the class names ?
Maybe submit patch to JDT for that ?
- ReferenceType.allLineLocations() throws an AbsentInformationException 
when at least one of the methods of the type has no line info. The JDK
implementation returns all line info that's available and only throws an exception when NONE of the methods have line locations. The JDI Javadoc is a bit vague about this, but I would consider this as a JDT bug. (The point is that the Script* classes generated by Nashorn do contain line locations only for those methods corresponding to JavaScript functions or top-level 
scripts, and there are some other methods without line info.) As a
workaround, I iterate over the methods myself.


sounds like another bugfix for JDT.
Now my next idea is to create a new IJavaScriptDebugTarget implementation which delegates to the JDIDebugTarget, transforming JavaScript debugger commands/events to JDI commands and events and vice versa. Does this make 
sense?


I think so - can you share your code somewhere ?

Maybe push to gerrit  ?
/max



Regards,
Harald



2015-03-17 11:37 GMT+01:00 Max Rydahl Andersen <manderse@xxxxxxxxxx>:


Okey, so I reached out to netbeans guys and he confirmed to me it is
really underdocumented, but
apparently the DebuggerSupport class is part of the key and the only known 
public documentation for it
is in this example: https://github.com/wickund/nashornexamples

this is showing how a debugger can connect to nashorn over the debug
protocol.

Interested in picking up that challenge ?

/max


On 15 Mar 2015, at 9:27, Harald Wellmann wrote:


Yes, it's a normal JDI connection. And it doesn't "just work", I'm

afraid,
nor do I see why it might. I don't know how it works with JSPs. Do
compiled
JSP classes contain a stratum with JSP line info?
Yes, the sourcelocation info on class'es would have a filename:linenumber 
piece of info.

Nashorn script classes

only contain a Java stratum, as far as I can tell.
Yeah, I tried googling and apparently nashorn doesn't fit as smooth as 
rhino did.

I'm still looking and will ask around but I did find this jira:
https://bugs.openjdk.java.net/browse/JDK-8044798
which talks about jdk.nashorn.internal.runtime.DebuggerSupport being 
what is supposed to be used
for external debuggers.

I think thats what netbeans/intellij uses - but i'm not sure.

/max


Regards,

Harald
2015-03-15 0:12 GMT+01:00 Max Rydahl Andersen <manderse@xxxxxxxxxx>:
Is the connection made over normal jVm debugging ? Then my guess is that 
it should "just work". Like with when debugging java with jsps.
But otherwise it might be necessary to have both debuggers connected ? 

/max
http://about.me/maxandersen


On 14 Mar 2015, at 19:24, Harald Wellmann <hwellmann.de@xxxxxxxxx>



wrote:
Continuing a conversation [1] started in the JBoss Tools Forum, I would
like to discuss what it would take to support mixed JavaScript/Java 
debugging on Nashorn with JSDT.
This is a feature that works very smoothly in NetBeans, but is not
currently supported by official Eclipse projects or any third-party 
plugins, as it seems.



Scenario:
We are debugging a plain old Java application which embeds Nashorn via
javax.script.ScriptEngine and loads some JavaScript files. Some of the 
JavaScript functions call Java methods via Nashorn extensions.
Using the Eclipse debugger, we can set breakpoints both in JavaScript 


and Java sources and step through our application, from Java into
JavaScript and back into Java, with the appropriate source lines being 
highlighted in the editor.
In the call stack, we can see Java and JavaScript stack frames embodied
by method calls of generated Java classes. When selecting a stack frame corresponding to a JavaScript call, the variable inspector automatically switches from Java to JavaScript mode, so we can inspect JavaScript 
objects.





So far, I've experimented with JDI and
jdk.nashorn.internal.runtime.DebuggerSupport and I sort of understand 
how
to track scripts being loaded and how to map breakpoints to JavaScript 
source lines and vice versa.
I've taken a look at JSDT and JDT sources, and I'm not quite sure how 


this mixed source scenario would fit into the existing approaches.
Implementing a new JSDI adapter for Nashorn along the lines of the 
Rhino


debugger would only cover the JavaScript part.
Would it be possible to start with a JDT debug launcher and extend it 
or


create some kind of mixin to switch between the Nashorn/Java and
JavaScript
aspects of the same application?



Are there any solutions for other JVM languages supporting


mixed-language applications that might serve as an example?



[1] https://developer.jboss.org/message/920239

Best regards,
Harald
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/max
http://about.me/maxandersen




/max
http://about.me/maxandersen
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/max
http://about.me/maxandersen

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