Bug 505940 - Unnecessarily uploading records on first sync

Remove short-circuit logic of comparing number of keys for deepEquals and iterate through each key on both objects to make sure both have the same value.

source/modules/util.js

@@ -301,14 +301,25 @@ let Utils = {
     if (a === b)
       return true;
 
-    // Grab the keys from both sides
-    let [A, B] = [[i for (i in a)], [i for (i in b)]];
-    // Don't bother doing any more if they aren't objects with same # keys
-    if (typeof a != "object" || typeof b != "object" || A.length != B.length)
+    // If they weren't equal, they must be objects to be different
+    if (typeof a != "object" || typeof b != "object")
       return false;
 
-    // Check if both sides have the same keys and same value for the key
-    return A.every(function(A) B.some(function(B) A == B && eq(a[A], b[B])));
+    // But null objects won't have properties to compare
+    if (a === null || b === null)
+      return false;
+
+    // Make sure all of a's keys have a matching value in b
+    for (let k in a)
+      if (!eq(a[k], b[k]))
+        return false;
+
+    // Do the same for b's keys but skip those that we already checked
+    for (let k in b)
+      if (!(k in a) && !eq(a[k], b[k]))
+        return false;
+
+    return true;
   },
 
   deepCopy: function Weave_deepCopy(thing, noSort) {

tests/unit/test_utils_deepEquals.js

@@ -39,4 +39,17 @@ function run_test() {
     _("Actual matches:", numMatch);
     do_check_eq(numMatch, expect);
   });
+
+  _("Make sure adding undefined properties doesn't affect equalness");
+  let a = {};
+  let b = { a: undefined };
+  do_check_true(Utils.deepEquals(a, b));
+  a.b = 5;
+  do_check_false(Utils.deepEquals(a, b));
+  b.b = 5;
+  do_check_true(Utils.deepEquals(a, b));
+  a.c = undefined;
+  do_check_true(Utils.deepEquals(a, b));
+  b.d = undefined;
+  do_check_true(Utils.deepEquals(a, b));
 }