fix(scope): support watching functions

currently we run into infinite digest if a function is being
watched as an expression. This is because we generate bound
function wrapper when the watch is processed via parser.

I'm not too keen on the solution because it relies on the unbound
fn that is being exposed for other reasons, but I can't think
of a better way to deal with this right now

Author: IgorMinar

src/Angular.js

@@ -655,28 +655,31 @@ function equals(o1, o2) {
   if (o1 === null || o2 === null) return false;
   if (o1 !== o1 && o2 !== o2) return true; // NaN === NaN
   var t1 = typeof o1, t2 = typeof o2, length, key, keySet;
-  if (t1 == t2 && t1 == 'object') {
-    if (isArray(o1)) {
-      if ((length = o1.length) == o2.length) {
-        for(key=0; key<length; key++) {
-          if (!equals(o1[key], o2[key])) return false;
+  if (t1 == t2) {
+    if (t1 == 'object') {
+      if (isArray(o1)) {
+        if ((length = o1.length) == o2.length) {
+          for(key=0; key<length; key++) {
+            if (!equals(o1[key], o2[key])) return false;
+          }
+          return true;
         }
-        return true;
-      }
-    } else {
-      if (isScope(o1) || isScope(o2) || isWindow(o1) || isWindow(o2)) return false;
-      keySet = {};
-      for(key in o1) {
-        if (key.charAt(0) !== '$' && !isFunction(o1[key]) && !equals(o1[key], o2[key])) {
-          return false;
+      } else {
+        if (isScope(o1) || isScope(o2) || isWindow(o1) || isWindow(o2)) return false;
+        keySet = {};
+        for(key in o1) {
+          if (key.charAt(0) !== '$' && !isFunction(o1[key]) && !equals(o1[key], o2[key])) {
+            return false;
+          }
+          keySet[key] = true;
         }
-        keySet[key] = true;
-      }
-      for(key in o2) {
-        if (!keySet[key] && key.charAt(0) !== '$' && !isFunction(o2[key])) return false;
+        for(key in o2) {
+          if (!keySet[key] && key.charAt(0) !== '$' && !isFunction(o2[key])) return false;
+        }
+        return true;
       }
-      return true;
     }
+    if (t1 == 'function' && o1.$unboundFn) return o1.$unboundFn === o2.$unboundFn;
   }
   return false;
 }

test/service/scopeSpec.js

@@ -248,6 +248,22 @@ describe('Scope', function() {
     }));
 
 
+    it('should watch functions', function() {
+      module(provideLog);
+      inject(function($rootScope, log) {
+        $rootScope.fn = function() {return 'a'};
+        $rootScope.$watch('fn', function(scope, fn) {
+          log(fn());
+        });
+        $rootScope.$digest();
+        expect(log).toEqual('a');
+        $rootScope.fn = function() {return 'b'};
+        $rootScope.$digest();
+        expect(log).toEqual('a; b');
+      })
+    });
+
+
     it('should prevent $digest recursion', inject(function($rootScope) {
       var callCount = 0;
       $rootScope.$watch('name', function() {