Xtext Content Assist: Escape identifiers conflicting with keywords

I have faced in Spray the situation that a segment of a package name of a qualified Java type conflicts with a keyword of the Spray language. Specifically you can refer to custom features with the custom keyword, and the referred type was in a package containing also the name custom.

When inserting the proposed qualified name this results in an error due to the keyword collision.

The qualified name is usually combined through a sequence of ID rules, which allows escaping an identifier by prefixing it with the ^ character in the case of conflict with a keyword.

For content assist it would now be useful if the inserted string would be automatically escaped. So here is a way to solve this.

My first approach was to override the completeJvmParameterizedTypeReference_Type() method from the proposal provider and modify the proposals through a custom ICompletionProposalAcceptor. Sebastian Zarnekow commented that the proper way would be to register a IValueConverter for QualifiedName. I tried to do so, but was not successful. Actually there is already an QualifiedNameValueConverter registered.

My next solution is now to subclass JdtTypesProposalProvider and pass a custom IValueConverter. The overridden methods just pass null as converter, thus do no conversion. I am reusing the QualifiedNameValueConverter here, since it does the necessary keyword escaping.

public class SprayJdtTypesProposalProvider extends JdtTypesProposalProvider {
    @Inject
    private QualifiedNameValueConverter qnValueConverter;

    /**
     * Overridden to pass a default value converter
     */
    @Override
    public void createSubTypeProposals(JvmType superType, ICompletionProposalFactory proposalFactory, ContentAssistContext context, EReference typeReference, Filter filter, ICompletionProposalAcceptor acceptor) {
        createSubTypeProposals(superType, proposalFactory, context, typeReference, filter, getConverter(), acceptor);
    }

    /**
     * Overridden to pass a default value converter
     */
    @Override
    public void createTypeProposals(ICompletionProposalFactory proposalFactory, ContentAssistContext context, EReference typeReference, Filter filter, ICompletionProposalAcceptor acceptor) {
        createTypeProposals(proposalFactory, context, typeReference, filter, getConverter(), acceptor);
    }

    private AbstractValueConverter<String> getConverter() {
        return new AbstractValueConverter<String>() {
            /**
             * Remove ^ character from escaped segments
             */
            @Override
            public String toValue(String string, INode node) throws ValueConverterException {
                return string.replace("^", "");
            }

            /**
             * Escape segments colliding with keywords with ^ character
             */
            @Override
            public String toString(String value) throws ValueConverterException {
                // this converter will escape keywords with ^
                return qnValueConverter.toString(value);
            }
        };
    }
}

This custom implementation must be bound to the UI module:

public class SprayUiModule extends AbstractSprayUiModule {
    @Override
    public Class<? extends ITypesProposalProvider> bindITypesProposalProvider() {
        return SprayJdtTypesProposalProvider.class;
    }
}

Now the inserted qualified type name will be automatically replaced.

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2 thoughts on “Xtext Content Assist: Escape identifiers conflicting with keywords

  1. Hi Karsten, Xtext will escape the identifiers automatically if you register a valid value converter for your data type rule for QualifiedNames. There is usually no need for special treatment in the proposal provider.

    • Argh! This would be of course the right solution. I will remove my ugly workaround. Thanks for the hint! At least I could reuse the mentioned function for that.

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