Saxon

I am experimenting with running Saxon Java HE (using 11.6 at the moment) in the browser, using a tool CheerpJ (in a preview version 3) that compiles Java (class/jars) to web assembly and runs that. so far with mostly surprising/promising results.

For some reasons (that might be due to deficits/shortcomings of CheerpJ, I am investigating partly in their discord server, partly here) trying to use toString() on an XdmValue gives an UnsupportedOperationException, a stack trace is like

Exception in thread "Thread-0" java.lang.UnsupportedOperationException at java.lang.Exception.<init>(Unknown Source) at java.lang.RuntimeException.<init>(Unknown Source) at java.lang.UnsupportedOperationException.<init>(Unknown Source) at net.sf.saxon.event.Receiver.append(Unknown Source) at net.sf.saxon.event.Receiver.append(Unknown Source) at net.sf.saxon.event.SequenceCopier$$Lambda$16.accept(Unknown Source) at net.sf.saxon.om.SequenceTool.supply(Unknown Source) at net.sf.saxon.event.SequenceCopier.copySequence(Unknown Source) at net.sf.saxon.s9api.XdmValue.toString(Unknown Source) at org.example.Main.main(Unknown Source)

Saxon's Receiver in the default implementation in that interface https://saxonica.plan.io/projects/saxonmirrorhe/repository/he/revisions/he_mirror_saxon_11_6/entry/src/main/java/net/sf/saxon/event/Receiver.java#L176 does indeed throw new UnsupportedOperationException(); but when running Saxon code with a "normal" Java 8 JRE/JDK I never get such an exception, instead it seems some Receiver implementation is used that knows to serialize any XdmItems in the XdmValue sequence to a String, I think that is done in https://saxonica.plan.io/projects/saxonmirrorhe/repository/he/revisions/he_mirror_saxon_11_6/entry/src/main/java/net/sf/saxon/s9api/XdmValue.java#L300 with e.g.

    public String toString() {
        try {
            Configuration config = null;
            SequenceIterator iter = value.iterate();
            Item item;
            while ((item = iter.next()) != null) {
                if (item instanceof NodeInfo) {
                    config = ((NodeInfo)item).getConfiguration();
                    break;
                }
            }
            if (config == null) {
                config = Configuration.newConfiguration();
            }
            StringWriter writer = new StringWriter();
            StreamResult result = new StreamResult(writer);
            SerializationProperties properties = new SerializationProperties();
            properties.setProperty(OutputKeys.METHOD, "adaptive");
            properties.setProperty(OutputKeys.INDENT, "true");
            properties.setProperty(OutputKeys.OMIT_XML_DECLARATION, "true");
            Receiver r = config.getSerializerFactory().getReceiver(result, properties);
            SequenceCopier.copySequence(value.iterate(), r);
            return writer.toString();
        } catch (XPathException e) {
            return super.toString();
        }

    }

Does anyone familiar with the Saxon code have an idea how/whether perhaps Receiver r = config.getSerializerFactory().getReceiver(result, properties); could go wrong to use the default append from the interface?

I understand this is not an issue in the Saxon code, only when run in that experimental Java to web assembly environment, but as I am bit lost in Saxon's source once it goes below the net.sf.saxon.s9api level I am hoping someone here can give me some pointers or speculation as to what might fail.