From 6cc809b9562b32a867be122fdcb68fd06f358a8b Mon Sep 17 00:00:00 2001
From: David Glasser <glasser@meteor.com>
Date: Tue, 11 Dec 2012 17:26:56 -0800
Subject: [PATCH] Avoid unnecessary equality comparison in clearField.

Minor test changes.
---
 packages/livedata/livedata_server.js    | 12 ++++++----
 packages/livedata/session_view_tests.js | 30 ++++++++++++++-----------
 2 files changed, 25 insertions(+), 17 deletions(-)

diff --git a/packages/livedata/livedata_server.js b/packages/livedata/livedata_server.js
index b0497b6685..8620b4114a 100644
--- a/packages/livedata/livedata_server.js
+++ b/packages/livedata/livedata_server.js
@@ -20,11 +20,14 @@ _.extend(Meteor._SessionDocumentView.prototype, {
     if (!precedenceList) {
       throw new Error("Could not find field to clear " + key);
     }
-    var old = precedenceList[0];
-    var precedence;
+    var removedValue = undefined;
     for (var i = 0; i < precedenceList.length; i++) {
-      precedence = precedenceList[i];
+      var precedence = precedenceList[i];
       if (precedence.subscriptionId === subscriptionId) {
+        // The view's value can only change if this subscription is the one that
+        // used to have precedence.
+        if (i === 0)
+          removedValue = precedence.value;
         precedenceList.splice(i, 1);
         break;
       }
@@ -32,7 +35,8 @@ _.extend(Meteor._SessionDocumentView.prototype, {
     if (_.isEmpty(precedenceList)) {
       delete self.dataByKey[key];
       clearCollector.push(key);
-    } else if (!_.isEqual(old.value, precedenceList[0].value)) {
+    } else if (removedValue !== undefined &&
+               !_.isEqual(removedValue, precedenceList[0].value)) {
       changeCollector[key] = precedenceList[0].value;
     }
   },
diff --git a/packages/livedata/session_view_tests.js b/packages/livedata/session_view_tests.js
index 2832a5deb4..063c9b51cb 100644
--- a/packages/livedata/session_view_tests.js
+++ b/packages/livedata/session_view_tests.js
@@ -11,25 +11,25 @@ var newView = function(test) {
       results.push({fun: 'removed', ids: ids});
     }
   });
-  var ret = {
+  var v = {
     view: view,
     results: results
   };
   _.each(["added", "changed", "removed"], function (it) {
-    ret[it] = _.bind(view[it], view);
+    v[it] = _.bind(view[it], view);
   });
-  ret.expectResult = function (result) {
+  v.expectResult = function (result) {
     test.equal(results.shift(), result);
   };
-  ret.expectNoResult = function () {
+  v.expectNoResult = function () {
     test.equal(results, []);
   };
-  ret.drain = function() {
+  v.drain = function() {
     var ret = results;
     results = [];
     return ret;
   };
-  return ret;
+  return v;
 };
 
 Tinytest.add('livedata - sessionview - exists reveal', function (test) {
@@ -150,7 +150,7 @@ Tinytest.add('livedata - sessionview - field clear reveal', function (test) {
   v.expectNoResult();
 });
 
-Tinytest.add('livedata - sessionview - change to cannonical value produces no change', function (test) {
+Tinytest.add('livedata - sessionview - change to canonical value produces no change', function (test) {
   var v = newView(test);
 
   v.added("A", {_id: "A1", foo: "bar"});
@@ -159,13 +159,17 @@ Tinytest.add('livedata - sessionview - change to cannonical value produces no ch
 
 
   v.added("B", {_id: "A1", foo: "baz"});
-  var cannon = "bar";
-  if (!_.isEmpty(v.drain())) {
+  var canon = "bar";
+  var maybeResults = v.drain();
+  if (!_.isEmpty(maybeResults)) {
     // if something happened, it was a change message to baz.
-    // if nothing did, cannon is still bar.
-    cannon = "baz";
+    // if nothing did, canon is still bar.
+    test.length(maybeResults, 1);
+    test.equal(maybeResults[0], {fun: 'added', id: "A1", changed: {foo: "baz"},
+                                 cleared: []});
+    canon = "baz";
   }
-  v.changed("B", "A1", {foo: cannon}, []);
+  v.changed("B", "A1", {foo: canon}, []);
   v.expectNoResult();
 
   v.removed("A", ["A1"]);
@@ -175,7 +179,7 @@ Tinytest.add('livedata - sessionview - change to cannonical value produces no ch
   v.expectNoResult();
 });
 
-Tinytest.add('livedata - sessionview - new field of cannonical value produces no change', function (test) {
+Tinytest.add('livedata - sessionview - new field of canonical value produces no change', function (test) {
   var v = newView(test);
 
   v.added("A", {_id: "A1", foo: "bar"});