Saxon

When resolving reflexive extension functions, Saxon makes no attempt to exclude Java synthetic methods from its search. Since a synthetic method can have the same name and argument types as a "real" method on the same class, this can cause the search for a method to fail saying that there is more than one candidate, and insufficient type information to disambiguate them. To demonstrate the problem:

package z;
public interface Foo<T> {
  T foo();
}

package z;
public class MyFoo implements Foo<String> {
  String foo() { return "foo"; }
}

XSLT:
<xsl:stylesheet 
  xmlns:xsl="http://www.w3.org/1999/XSL/Transform" 
  xmlns:z="java:z.MyFoo"
  version="2.0">

  <xsl:variable name="my" select="z:new()" />
  <xsl:value-of select="z:foo($my)" />
  
</xsl:stylesheet>