[JXPATH-204] Eagerly evaluate UnionContext before returning its value

src/main/java/org/apache/commons/jxpath/ri/axes/UnionContext.java

@@ -48,6 +48,17 @@ public int getDocumentOrder() {
         return contexts.length > 1 ? 1 : super.getDocumentOrder();
     }
 
+    @Override
+    public Object getValue() {
+        // JXPATH-204: the node set is built lazily inside setPosition(), so
+        // force it to be populated before delegating, otherwise callers that
+        // read the value without first iterating (e.g. an extension
+        // function receiving this context as an argument) see an empty
+        // NodeSet.
+        getContextNodeList();
+        return super.getValue();
+    }
+
     @Override
     public boolean setPosition(final int position) {
         if (!prepared) {

src/test/java/org/apache/commons/jxpath/ri/compiler/ExtensionFunctionTest.java

@@ -283,4 +283,13 @@ void testStaticMethodLookupWithExpressionContext() {
         final Function func = functions.getFunction("test", "path", args);
         assertEquals("1", func.invoke(new Context(Integer.valueOf(1)), args), "test:path()");
     }
-}
+
+    @Test
+    void testUnionOperatorArgument() {
+        // JXPATH-204: UnionContext computes its node list lazily (only inside
+        // setPosition()), so a custom function invoked with a union ('|')
+        // expression as an argument used to see an empty NodeSet instead of
+        // the union's actual nodes.
+        assertXPathValue(context, "test:countPointers(/beans[1] | /beans[2])", Integer.valueOf(2));
+    }
+}