From 0e248f5a3f8b86d2d55540cc70d9460b5b45ca00 Mon Sep 17 00:00:00 2001
From: Tim van der Lippe <tvanderlippe@gmail.com>
Date: Fri, 30 Oct 2015 22:53:25 +0100
Subject: [PATCH] Produce nicer error on malformed observer

---
 src/standard/effectBuilder.html |  5 +++++
 test/unit/notify-path.html      | 18 ++++++++++++++++++
 2 files changed, 23 insertions(+)

diff --git a/src/standard/effectBuilder.html b/src/standard/effectBuilder.html
index b86d6e801f..27730ec447 100644
--- a/src/standard/effectBuilder.html
+++ b/src/standard/effectBuilder.html
@@ -106,6 +106,11 @@
 
     _addComplexObserverEffect: function(observer) {
       var sig = this._parseMethod(observer);
+
+      if (!sig) {
+        throw new Error("Malformed observer expression '" + observer + "'");
+      }
+
       for (var i=0, arg; (i<sig.args.length) && (arg=sig.args[i]); i++) {
         this._addPropertyEffect(arg.model, 'complexObserver', {
           method: sig.method,
diff --git a/test/unit/notify-path.html b/test/unit/notify-path.html
index b0997f3436..74f24c8233 100644
--- a/test/unit/notify-path.html
+++ b/test/unit/notify-path.html
@@ -1044,6 +1044,24 @@
 
 });
 
+suite('malformed observers', function() {
+  test('has nice message on failure', function() {
+    var thrown = false;
+
+    try {
+      Polymer({
+        is: 'x-broken',
+        observers: ['foo(missingParenthesis']
+      });
+    } catch (e) {
+      assert.equal(e.message, "Malformed observer expression 'foo(missingParenthesis'");
+      thrown = true;
+    }
+
+    assert.equal(thrown, true, "No exception thrown when parsing malformed observer");
+  });
+});
+
 </script>
 
 </body>