Fix bug in polymer expressions where input-value bindings are incorrectly

pkg/polymer_expressions/test/bindings_test.dart

+// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+library bindings_test;
+
+import 'dart:async';
+import 'dart:html';
+import 'package:mdv/mdv.dart' as mdv;
+import 'package:observe/observe.dart';
+import 'package:observe/src/microtask.dart';
+import 'package:polymer_expressions/polymer_expressions.dart';
+import 'package:unittest/html_config.dart';
+import 'package:unittest/unittest.dart';
+
+main() {
+  mdv.initialize();
+  useHtmlConfiguration();
+
+  group('cursor position tests', () {
+    var testDiv;
+    setUp(() {
+      document.body.append(testDiv = new DivElement());
+    });
+
+    tearDown(() {
+      testDiv.remove();
+      testDiv = null;
+    });
+
+    test('cursor position test', wrapMicrotask(() {
+      var model = new NotifyModel('abcde');
+      var template = new Element.html(
+          '<template><input id="i1" value={{x}}></template>');
+      testDiv.append(template.createInstance(model, new PolymerExpressions()));
+
+      performMicrotaskCheckpoint();
+      var el = testDiv.query("#i1");
+      var subscription = el.onInput.listen(expectAsync1((_) {
+        performMicrotaskCheckpoint();
+      }, count: 1));
+      el.focus();
+
+      expect(el.value, 'abcde');
+      expect(model.x, 'abcde');
+  
+      el.selectionStart = 3;
+      el.selectionEnd = 3;
+      expect(el.selectionStart, 3);
+      expect(el.selectionEnd, 3);
+
+      el.value = 'abc de';
+      // Updating the input value programatically (even to the same value in
+      // Chrome) loses the selection position.
+      expect(el.selectionStart, 6);
+      expect(el.selectionEnd, 6);
+
+      el.selectionStart = 4;
+      el.selectionEnd = 4;
+
+      expect(model.x, 'abcde');
+      el.dispatchEvent(new Event('input'));
+      expect(model.x, 'abc de');
+      expect(el.value, 'abc de');
+
+      // But propagating observable values through reassign the value and
+      // selection will be preserved.
+      expect(el.selectionStart, 4);

[Siggi Cherem (dart-lang), 2013/10/10 00:49:48]

without the fix, this returns 6.

+      expect(el.selectionEnd, 4);
+
+      subscription.cancel();
+    }));
+  });
+}
+
+class NotifyModel extends ChangeNotifierBase {
+  var _x;
+  NotifyModel([this._x]);
+
+  get x => _x;
+  set x(value) {
+    _x = notifyPropertyChange(const Symbol('x'), _x, value);
+  }
+}