evaluateFirst call returns zero results for "//*" xpath query

[mykola-mokhnach]

We are using JDOM2/Jaxen combination in our project and it turns out, that //* xpath query returns all XML nodes if called via XPathExpression.evaluate, but zero results are returned if XPathExpression.evaluateFirst is called with the same argument. More details and CI results at:
appium/appium-uiautomator2-server#238

Moved from jaxen-xpath/jaxen#18

[hunterhacker]

I tried to repro the issue and failed.

import java.io.*;
import org.jdom2.*;
import org.jdom2.output.*;
import org.jdom2.xpath.*;

public class Test {
  public static void main(String[] args) throws IOException {
    Document doc = new Document()
      .addContent(new Element("root")
      .addContent(new Element("child")
      .addContent(new Element("subchild"))));

    System.out.println(XPathFactory.instance().compile("//*").evaluateFirst(doc));
  }
}

Produces:

[Element: <root/>]

Are you applying a Filter to the XPath? Note the Javadocs on the evaluateFirst() function:

     * Return the first value in the XPath query result set type-cast to the
     * return type of this XPathExpression.
     * <p>
     * The concept of the 'first' result is applied before any JDOM Filter is
     * applied. Thus, if the underlying XPath query has some results, the first
     * result is sent through the filter. If it matches it is returned, if it
     * does not match, then null is returned (even if some subsequent result
     * underlying XPath result would pass the filter).
     * <p>
     * This allows the XPath implementation to optimise the evaluateFirst method
     * by potentially using 'short-circuit' conditions in the evaluation.

[mykola-mokhnach]

Thanks for your investigation @hunterhacker
I suppose It might be an issue on our side.