Missing properties are not enumerable when checking enumerability

When checking property enumerability
_(`Object.prototype.propertyIsEnumerable`)_ on a `String`, missing properties
should return `false` instead of throwing a `Property {0} not found.` exception.

Fixes mozilla#415

src/org/mozilla/javascript/NativeObject.java

@@ -181,20 +181,31 @@ public Object execIdCall(IdFunctionObject f, Context cx, Scriptable scope,
                 }
             } else {
                 String s = ScriptRuntime.toStringIdOrIndex(cx, arg);
-                if (s == null) {
-                    int index = ScriptRuntime.lastIndexResult(cx);
-                    result = thisObj.has(index, thisObj);
-                    if (result && thisObj instanceof ScriptableObject) {
-                        ScriptableObject so = (ScriptableObject) thisObj;
-                        int attrs = so.getAttributes(index);
-                        result = ((attrs & ScriptableObject.DONTENUM) == 0);
+                // When checking if a property is enumerable, a missing property should return "false" instead of
+                // throwing an exception.  See: https://github.com/mozilla/rhino/issues/415
+                try {
+                    if (s == null) {
+                        int index = ScriptRuntime.lastIndexResult(cx);
+                        result = thisObj.has(index, thisObj);
+                        s = Integer.toString(index);
+                        if (result && thisObj instanceof ScriptableObject) {
+                            ScriptableObject so = (ScriptableObject) thisObj;
+                            int attrs = so.getAttributes(index);
+                            result = ((attrs & ScriptableObject.DONTENUM) == 0);
+                        }
+                    } else {
+                        result = thisObj.has(s, thisObj);
+                        if (result && thisObj instanceof ScriptableObject) {
+                            ScriptableObject so = (ScriptableObject) thisObj;
+                            int attrs = so.getAttributes(s);
+                            result = ((attrs & ScriptableObject.DONTENUM) == 0);
+                        }
                     }
-                } else {
-                    result = thisObj.has(s, thisObj);
-                    if (result && thisObj instanceof ScriptableObject) {
-                        ScriptableObject so = (ScriptableObject) thisObj;
-                        int attrs = so.getAttributes(s);
-                        result = ((attrs & ScriptableObject.DONTENUM) == 0);
+                } catch (EvaluatorException ee) {
+                    if (ee.getMessage().startsWith(ScriptRuntime.getMessage1("msg.prop.not.found", s))) {
+                        result = false;
+                    } else {
+                        throw ee;
                     }
                 }
             }

testsrc/org/mozilla/javascript/tests/es5/StringMissingPropertyIsNotEnumerableTest.java

@@ -0,0 +1,26 @@
+package org.mozilla.javascript.tests.es5;
+
+import org.junit.Test;
+import org.mozilla.javascript.NativeObject;
+
+import static org.junit.Assert.assertFalse;
+import static org.mozilla.javascript.tests.Evaluator.eval;
+
+/**
+ * When calling <b>propertyIsEnumerable</b> on a <b>String</b>, missing properties should return <b>false</b> instead of
+ * throwing a <b>Property {0} not found.</b> exception.
+ *
+ * @see <a href="https://github.com/mozilla/rhino/issues/415">https://github.com/mozilla/rhino/issues/415</a>
+ */
+public class StringMissingPropertyIsNotEnumerableTest {
+
+  @Test
+  public void testStringMissingPropertyIsNotEnumerable() {
+    NativeObject object = new NativeObject();
+
+    Object result = eval("'s'.propertyIsEnumerable(0)", "obj", object);
+
+    assertFalse((Boolean)result);
+  }
+
+}