check before trying to extend objects

stack-chain.js

@@ -117,9 +117,11 @@ function prepareStackTrace(error, originalFrames) {
   frames = frames.slice(0, Error.stackTraceLimit);
 
   // Set the callSite property
-  // But only if it havn't been explicitly set, otherwise
-  // error.stack would have unintended side effects
-  if (Object.getOwnPropertyDescriptor(error, "callSite") === undefined) {
+  // But only if it hasn't been explicitly set, otherwise
+  // error.stack would have unintended side effects. Check also for
+  // non-extensible/sealed objects, such as those from Google's Closure Library
+  if (Object.isExtensible(error) &&
+      (Object.getOwnPropertyDescriptor(error, "callSite") === undefined)) {
     error.callSite = {
       original: originalFrames,
       mutated: frames

test/simple/non-extensible-errors.js

@@ -0,0 +1,29 @@
+var test = require("tap").test;
+var chain = require('../../');
+
+test("non extensible Error objects don't throw", function(t) {
+  var error = new Error("don't extend me");
+  Object.preventExtensions(error)
+  t.doesNotThrow(function() {
+    error.stack;
+  });
+  t.end();
+});
+
+test('stack is correct on non extensible error object', function (t) {
+  var error = new Error("don't extend me");
+  Object.preventExtensions(error);
+
+  chain.format.replace(function () {
+    return 'good';
+  });
+
+  try {
+    t.equal(error.stack, 'good');
+  } catch (e) { t.ifError(e); }
+
+  chain.format.restore();
+
+  t.end();
+});
+