Make sure effect functions receive latest values

Fixes #3722

src/lib/bind/accessors.html

@@ -77,7 +77,9 @@
 
       _effectEffects: function(property, value, effects, old, fromAbove) {
         for (var i=0, l=effects.length, fx; (i<l) && (fx=effects[i]); i++) {
-          fx.fn.call(this, property, value, fx.effect, old, fromAbove);
+          // always send latest value for property
+          // if any previous effect has modified the value, given `value` will be stale
+          fx.fn.call(this, property, this[property], fx.effect, old, fromAbove);
         }
       },
 

test/unit/bind-elements.html

@@ -713,3 +713,31 @@
     });
   </script>
 </dom-module>
+
+<dom-module id="x-propagate">
+  <script>
+  Polymer({
+    is: 'x-propagate',
+    properties: {
+      value: {
+        type: Number,
+        value: -1
+      }
+    },
+    observers: [
+      '_boundOne(value)',
+      '_boundTwo(value)'
+    ],
+    _boundOne: function(value) {
+      if (value < 0) {
+        this.value = 1;
+      }
+    },
+    _boundTwo: function(value) {
+      if (value < 0) {
+        this.value = 2;
+      }
+    }
+  });
+  </script>
+</dom-module>

test/unit/bind.html

@@ -1023,6 +1023,14 @@
   });
 });
 
+suite('value propagation', function() {
+  test('effects forward propagate value', function() {
+    var el = document.createElement('x-propagate');
+    document.body.appendChild(el);
+    assert.equal(el.value, 1, 'observers did not receive latest value for property');
+  });
+});
+
 </script>
 
 </body>