Make Error.prototype.toString spec compliant; and fix various side-effect-free error printing metho…

test/mjsunit/error-constructors.js

Index: test/mjsunit/error-constructors.js
diff --git a/test/mjsunit/error-constructors.js b/test/mjsunit/error-constructors.js
index 0f3d74c960cfb04ad84be7919e5dca9eeab8338e..5c2aac5b8703cb421a69066465d437c6aae9254f 100644
--- a/test/mjsunit/error-constructors.js
+++ b/test/mjsunit/error-constructors.js
@@ -69,9 +69,11 @@ try {
 assertTrue(e.hasOwnProperty('stack'));
 
 // Check that intercepting property access from toString is prevented for
-// compiler errors. This is not specified, but allowing interception
-// through a getter can leak error objects from different
-// script tags in the same context in a browser setting.
+// compiler errors. This is not specified, but allowing interception through a
+// getter can leak error objects from different script tags in the same context
+// in a browser setting. Use Realm.eval as a proxy for loading scripts. We
+// ignore the exception thrown from it since that would not be catchable from
+// user-land code.
 var errors = [SyntaxError, ReferenceError, TypeError, RangeError, URIError];
 var error_triggers = ["syntax error",
                       "var error = reference",
@@ -79,39 +81,12 @@ var error_triggers = ["syntax error",
                       "String.fromCodePoint(0xFFFFFF)",
                       "decodeURI('%F')"];
 for (var i in errors) {
-  var name = errors[i].name;
-
   // Monkey-patch prototype.
-  var props = ["name", "message", "stack"];
-  for (var j in props) {
-    errors[i].prototype.__defineGetter__(props[j], fail);
+  for (var prop of ["name", "message", "stack"]) {
+    errors[i].prototype.__defineGetter__(prop, fail);
   }
   // String conversion should not invoke monkey-patched getters on prototype.
-  var error;
-  try {
-    eval(error_triggers[i]);
-  } catch (e) {
-    error = e;
-  }
-  assertTrue(error.toString().startsWith(name));
-
-  // Deleting message on the error (exposing the getter) is fine.
-  delete error.message;
-  assertEquals(name, error.toString());
-
-  // Custom properties shadowing the name are fine.
-  var myerror = { name: "myerror", message: "mymessage"};
-  myerror.__proto__ = error;
-  assertEquals("myerror: mymessage", myerror.toString());
-
-  // Custom getters in actual objects are welcome.
-  error.__defineGetter__("name", function() { return "mine"; });
-  assertEquals("mine", error.toString());
-
-  // Custom properties shadowing the name are fine.
-  var myerror2 = { message: "mymessage"};
-  myerror2.__proto__ = error;
-  assertEquals("mine: mymessage", myerror2.toString());
+  assertThrows(()=>Realm.eval(0, error_triggers[i]));
 }
 
 // Monkey-patching non-internal errors should still be observable.