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Exception when serializing [message #774802]

Wed, 04 January 2012 16:42

Thomas Williams

Messages: 15
Registered: January 2012

Junior Member

Dear Xtexters,

I'm having problems doing a round-trip of parse and serialize using XText 2.1.1.

Pared down to a minimum my grammar looks like this:

grammar psenterprise.xtext.GpromsLanguage with org.eclipse.xtext.common.Terminals 

import "some url which the forum won't allow me to post" as ecore

generate gpromsLanguage "some other url which the forum won't allow me to post"

GeneralProcessModellingSystem:
	variableTypeEntity=VariableTypeEntity ;

VariableTypeEntity:
    name = ID
    '=' default=RealNumber
    ':' lowerBound=RealNumber 
    ':' upperBound=RealNumber 
    ("UNIT" '=' unit=STRING)? ;

RealNumber returns ecore::EDouble:
	('-')? INT ( '.' INT )? ;

And I am trying to parse and then serialize a String:

private static String LANGUAGE_TEXT = "GasConcentration = 1.0 : 0.0 : 10.0 UNIT = \"mol/m3\"";

public static void main(String[] args) throws IOException {

	new org.eclipse.emf.mwe.utils.StandaloneSetup().setPlatformUri("../");
	Injector injector = new GpromsLanguageStandaloneSetup().createInjectorAndDoEMFRegistration();
	XtextResourceSet resourceSet = injector.getInstance(XtextResourceSet.class);
	resourceSet.addLoadOption(XtextResource.OPTION_RESOLVE_ALL, Boolean.TRUE);
	Resource resource = resourceSet.createResource(URI.createURI("dummy:/example.gPROMS"));

	InputStream in = new ByteArrayInputStream(LANGUAGE_TEXT.getBytes());

	resource.load(in, resourceSet.getLoadOptions());
	if (!resource.getErrors().isEmpty()) {
		System.out.println(resource.getErrors());
		return;
	}

	GeneralProcessModellingSystem gpms = (GeneralProcessModellingSystem) resource.getContents().get(0);		
	VariableTypeEntity variableTypeEntity = gpms.getVariableTypeEntity();
	System.out.println(org.eclipse.xtext.util.EmfFormatter.objToStr(gpms));
	Serializer serializer = injector.getInstance(Serializer.class);  
	String s = serializer.serialize(gpms);
	System.out.println(s);
}

I get the following output from EmfFormatter.objToStr(gpms):

GeneralProcessModellingSystem {
    cref VariableTypeEntity variableTypeEntity VariableTypeEntity {
        attr EString name 'GasConcentration'
        attr EDouble default '1.0'
        attr EDouble upperBound '10.0'
        attr EString unit 'mol/m3'
    }
}

Note the unexpected absence of the "lowerBound".

And then the serialize() call fails with:

Exception in thread "main" java.lang.RuntimeException: Could not serialize EObject via backtracking.
Constraint: null name=ID default=RealNumber lowerBound=RealNumber upperBound=RealNumber unit=STRING? null
Values: name(1), default(1), upperBound(1), unit(1)
Semantic Object: GeneralProcessModellingSystem.variableTypeEntity->VariableTypeEntity'GasConcentration'
Context: VariableTypeEntity
	at org.eclipse.xtext.serializer.diagnostic.ISerializationDiagnostic$ExceptionThrowingAcceptor.accept(ISerializationDiagnostic.java:70)
	at org.eclipse.xtext.serializer.sequencer.BacktrackingSemanticSequencer.createSequence(BacktrackingSemanticSequencer.java:425)
	at psenterprise.xtext.serializer.AbstractGpromsLanguageSemanticSequencer.sequence_VariableTypeEntity(AbstractGpromsLanguageSemanticSequencer.java:112)
	at psenterprise.xtext.serializer.AbstractGpromsLanguageSemanticSequencer.createSequence(AbstractGpromsLanguageSemanticSequencer.java:67)
	at org.eclipse.xtext.serializer.acceptor.SequenceFeeder.acceptEObjectRuleCall(SequenceFeeder.java:299)
	at org.eclipse.xtext.serializer.acceptor.SequenceFeeder.acceptRuleCall(SequenceFeeder.java:325)
	at org.eclipse.xtext.serializer.acceptor.SequenceFeeder.accept(SequenceFeeder.java:215)
	at psenterprise.xtext.serializer.AbstractGpromsLanguageSemanticSequencer.sequence_GeneralProcessModellingSystem(AbstractGpromsLanguageSemanticSequencer.java:102)
	at psenterprise.xtext.serializer.AbstractGpromsLanguageSemanticSequencer.createSequence(AbstractGpromsLanguageSemanticSequencer.java:60)
	at org.eclipse.xtext.serializer.impl.Serializer.serialize(Serializer.java:84)
	at org.eclipse.xtext.serializer.impl.Serializer.serialize(Serializer.java:103)
	at org.eclipse.xtext.serializer.impl.Serializer.serialize(Serializer.java:117)
	at org.eclipse.xtext.serializer.impl.Serializer.serialize(Serializer.java:50)
	at psenterprise.gparser.Main.serializeGPMS(Main.java:108)
	at psenterprise.gparser.Main.main(Main.java:53)

From reading other posts and web-pages I'm fairly certain this is something to do with the "lowerBound" being considered "transient?" because its value is equal to the default for EDouble but I haven't been able to determine what I'm supposed to do to work around this.

I have tried implementing:

public class GpromsLanguageTransientValueService extends DefaultTransientValueService{

	@Override
	public boolean isTransient(EObject owner, EStructuralFeature feature, int index) {
		System.out.println(owner);
		if (owner instanceof VariableTypeEntity && GpromsLanguagePackage.VARIABLE_TYPE_ENTITY__LOWER_BOUND == feature.getFeatureID()) {
			return false;
	    }
		return super.isTransient(owner, feature, index);
	}
}

And binding it with:

public class GpromsLanguageRuntimeModule extends psenterprise.xtext.AbstractGpromsLanguageRuntimeModule {

    @Override
    public Class<? extends ITransientValueService> bindITransientValueService() {
        return GpromsLanguageTransientValueService.class;
    }
}

And I can see that my TransientValueService is being called, but it's not fixing the problem.

Can anyone help?

Sincerely,

Tom

[Updated on: Wed, 04 January 2012 16:42]

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Re: Exception when serializing [message #775134 is a reply to message #774802]

Thu, 05 January 2012 12:03

Christian Dietrich

Messages: 13409
Registered: July 2009

Senior Member

Hi,

this is a bug in the new serializer. please file a ticket.
as a workaround

(1) change grammar to

RealNumber returns ecore::EDoubleObject:
	('-')? INT ( '.' INT )? ;

(2) use the old one

fragment = parseTreeConstructor.ParseTreeConstructorFragment {}

~Christian

Need professional support for Xtext, Xpand, EMF?
Go to: https://www.itemis.com/en/xtext/
Twitter : @chrdietrich
Blog : https://www.dietrich-it.de

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Re: Exception when serializing [message #775245 is a reply to message #775134]

Thu, 05 January 2012 16:23

Thomas Williams

Messages: 15
Registered: January 2012

Junior Member

Thanks Christian,

So that I can be sure of writing a usable bug-report can I request some clarification:

* Can you confirm that this is two different workarounds, not two steps to the same workaround - I did just (1) and that seems to have fixed the problem.
* Presumably this fix works because the default for an EDoubleObject is null rather than 0.0 so it's not being marked as a transient ?

Thanks,

Tom

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Re: Exception when serializing [message #775304 is a reply to message #775245]

Thu, 05 January 2012 18:41

Christian Dietrich

Messages: 13409
Registered: July 2009

Senior Member

Hi Tom

(1) and (2) are alternative solutions.
and yes "null" as default value does the trick. => it is more kind a workaround than a solution

~Christian

Need professional support for Xtext, Xpand, EMF?
Go to: https://www.itemis.com/en/xtext/
Twitter : @chrdietrich
Blog : https://www.dietrich-it.de

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Re: Exception when serializing [message #776873 is a reply to message #775304]

Mon, 09 January 2012 12:48

Thomas Williams

Messages: 15
Registered: January 2012

Junior Member

Hi Christian,

And is the fact that I was unable to solve the problem by implementing my own TransientValueService the same bug? a separate bug? or just an example of me misunderstanding the use of TransientValueService ?

Sincerely,

Tom

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Re: Exception when serializing [message #776886 is a reply to message #776873]

Mon, 09 January 2012 13:08

Christian Dietrich

Messages: 13409
Registered: July 2009

Senior Member

yes and no - the transient value service should have done this too.
but of course you should have implemented and bound the correct one (org.eclipse.xtext.serializer.sequencer.ITransientValueService)
it is imho a bug that the missleading org.eclipse.xtext.parsetree.reconstr.ITransientValueService has a binding in the DefaultRuntimeModule

Need professional support for Xtext, Xpand, EMF?
Go to: https://www.itemis.com/en/xtext/
Twitter : @chrdietrich
Blog : https://www.dietrich-it.de

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