Trigger sort after adds for efficient reordering

backbone.js

@@ -662,8 +662,8 @@
       push.apply(args, models);
       splice.apply(this.models, args);
 
-      // Sort the collection if appropriate.
-      if (needsSort && this.comparator && at == null) this.sort({silent: true});
+      // Silently sort the collection if appropriate.
+      if (needsSort &= this.comparator && at == null) this.sort({silent: true});
 
       if (options && options.silent) return this;
 
@@ -672,6 +672,9 @@
         model.trigger('add', model, this, options);
       }
 
+      // Trigger `sort` if the collection was sorted.
+      if (needsSort) this.trigger('sort', this, options);
+
       return this;
     },
 

test/collection.js

@@ -929,4 +929,15 @@ $(document).ready(function() {
     Backbone.ajax = ajax;
   });
 
+  test("`sort` is trigged on `add` when sorting occurs", 2, function () {
+    var collection = new (Backbone.Collection.extend({
+      comparator: 'id'
+    }))({id: 1, id: 2, id: 3});
+    collection.on('sort', function () { ok(1); });
+    collection.add({id: 4}); // trigger
+    collection.add({id: 1}, {merge: true}); // trigger
+    collection.add({id: 1}); // don't trigger
+    collection.add({id: 5}, {silent: true}); // don't trigger
+  });
+
 });