fix(change_detector): Fix for detecting NanN moves in collections

Closes dart-archive#1136

Author: vicb

lib/change_detection/dirty_checking_change_detector.dart

@@ -1343,7 +1343,8 @@ class _DuplicateItemRecordList {
       record._prevDup = null;
     } else {
       // adding a duplicate [ItemRecord] to the list
-      assert(record.item == _head.item);
+      assert(record.item ==  _head.item ||
+             record.item is num && record.item.isNaN && _head.item is num && _head.item.isNaN);
       if (insertBefore == null) {
         _tail._nextDup = record;
         record._prevDup = _tail;
@@ -1369,9 +1370,12 @@ class _DuplicateItemRecordList {
   ItemRecord get(item, int afterIndex) {
     ItemRecord record;
     for (record = _head; record != null; record = record._nextDup) {
-      if ((afterIndex == null || afterIndex < record.currentIndex) &&
-          identical(record.item, item)) {
-        return record;
+      if (afterIndex == null || afterIndex < record.currentIndex) {
+        if (identical(record.item, item) ||
+            record.item is String && item is String && record.item == item ||
+            record.item is num && record.item.isNaN && item is num && item.isNaN) {
+          return record;
+        }
       }
     }
     return null;
@@ -1414,10 +1418,12 @@ class _DuplicateItemRecordList {
  * The list of duplicates is implemented by [_DuplicateItemRecordList].
  */
 class DuplicateMap {
+  static final nanKey = const Object();
   final map = new HashMap<dynamic, _DuplicateItemRecordList>();
 
   void put(ItemRecord record, [ItemRecord insertBefore = null]) {
-    map.putIfAbsent(record.item, () => new _DuplicateItemRecordList()).add(record, insertBefore);
+    var key = _getKey(record.item);
+    map.putIfAbsent(key, () => new _DuplicateItemRecordList()).add(record, insertBefore);
   }
 
   /**
@@ -1427,9 +1433,10 @@ class DuplicateMap {
    * Use case: `[a, b, c, a, a]` if we are at index `3` which is the second `a` then asking if we
    * have any more `a`s needs to return the last `a` not the first or second.
    */
-  ItemRecord get(key, [int afterIndex]) {
+  ItemRecord get(value, [int afterIndex]) {
+    var key = _getKey(value);
     _DuplicateItemRecordList recordList = map[key];
-    return recordList == null ? null : recordList.get(key, afterIndex);
+    return recordList == null ? null : recordList.get(value, afterIndex);
   }
 
   /**
@@ -1438,10 +1445,11 @@ class DuplicateMap {
    * The list of duplicates also is removed from the map if it gets empty.
    */
   ItemRecord remove(ItemRecord record) {
-    assert(map.containsKey(record.item));
-    _DuplicateItemRecordList recordList = map[record.item];
+    var key = _getKey(record.item);
+    assert(map.containsKey(key));
+    _DuplicateItemRecordList recordList = map[key];
     // Remove the list of duplicates when it gets empty
-    if (recordList.remove(record)) map.remove(record.item);
+    if (recordList.remove(record)) map.remove(key);
     return record;
   }
 
@@ -1451,5 +1459,8 @@ class DuplicateMap {
     map.clear();
   }
 
+  /// Required to handle num.NAN as a Map value
+  dynamic _getKey(value) => value is num && value.isNaN ? nanKey : value;
+
   String toString() => "DuplicateMap($map)";
 }

test/change_detection/dirty_checking_change_detector_spec.dart

@@ -390,6 +390,21 @@ void testWithGetterFactory(FieldGetterFactory getterFactory) {
         expect(detector.collectChanges().moveNext()).toEqual(false);
       });
 
+      it('should detect [NaN] moves', () {
+        var list = [double.NAN, double.NAN];
+        detector..watch(list, null, null)..collectChanges();
+
+        list..clear()..addAll(['foo', double.NAN, double.NAN]);
+        var iterator = detector.collectChanges();
+        expect(iterator.moveNext()).toEqual(true);
+        expect(iterator.current.currentValue, toEqualCollectionRecord(
+            collection: ['foo[null -> 0]', 'NaN[0 -> 1]', 'NaN[1 -> 2]'],
+            previous: ['NaN[0 -> 1]', 'NaN[1 -> 2]'],
+            additions: ['foo[null -> 0]'],
+            moves: ['NaN[0 -> 1]', 'NaN[1 -> 2]'],
+            removals: []));
+      });
+
       it('should remove and add same item', () {
         var list = ['a', 'b', 'c'];
         var record = detector.watch(list, null, 'handler');