feat(NodeAttrs): Node attributes don't get initialized by NodeAttrs when

setting up observing.

In case an element does not have a value set for a propertyv, that
property is not automatically initialised. For example:

  <div test foo="bar">

will cause ElementBinder to register observer (which will in turn cause
initialisation) on property foo (of the directive) to bar, but if we try
using

  <div test>

foo property will not be initialised.

Closes #1001

Author: mvuksano

lib/core_dom/directive.dart

@@ -57,7 +57,10 @@ class NodeAttrs {
       if (_mustacheAttrs[attrName].isComputed) notifyFn(this[attrName]);
       _mustacheAttrs[attrName].notifyFn(true);
     } else {
-      notifyFn(this[attrName]);
+      if (element.attributes.containsKey(attrName)) {
+        var value = element.attributes[attrName];
+        notifyFn(this[attrName]);
+      }
     }
   }
 

lib/core_dom/element_binder.dart

@@ -104,9 +104,9 @@ class ElementBinder {
     dstPathFn.assign(controller, _parser(expression).bind(scope.context, ScopeLocals.wrapper));
   }
 
-
-  void _createAttrMappings(directive, scope, List<MappingParts> mappings, nodeAttrs, tasks) {
+  void _createAttrMappings(directive, scope, DirectiveRef ref, nodeAttrs, tasks) {
     Scope directiveScope; // Only created if there is a two-way binding in the element.
+    List<MappingParts> mappings = ref.mappings;
     for(var i = 0; i < mappings.length; i++) {
       MappingParts p = mappings[i];
       var attrName = p.attrName;
@@ -138,6 +138,10 @@ class ElementBinder {
       switch (p.mode) {
         case '@': // string
           var taskId = (tasks != null) ? tasks.registerTask() : 0;
+          if (ref.element is dom.Element &&
+              !(ref.element as dom.Element).attributes.containsKey(attrName)) {
+            tasks.completeTask(taskId);
+          }
           nodeAttrs.observe(attrName, (value) {
             dstAST.parsedExp.assign(directive, value);
             if (tasks != null) tasks.completeTask(taskId);
@@ -202,7 +206,7 @@ class ElementBinder {
 
       if (ref.mappings.isNotEmpty) {
         if (nodeAttrs == null) nodeAttrs = new _AnchorAttrs(ref);
-        _createAttrMappings(directive, scope, ref.mappings, nodeAttrs, tasks);
+        _createAttrMappings(directive, scope, ref, nodeAttrs, tasks);
       }
 
       if (directive is AttachAware) {

lib/directive/ng_model.dart

@@ -70,6 +70,7 @@ class NgModel extends NgControl implements AttachAware {
 
   void attach() {
     watchCollection = false;
+    _parentControl.addControl(this);
   }
 
   /**
@@ -130,7 +131,6 @@ class NgModel extends NgControl implements AttachAware {
   String get name => _name;
   void set name(value) {
     _name = value;
-    _parentControl.addControl(this);
   }
 
   // TODO(misko): could we get rid of watch collection, and just always watch the collection?

lib/directive/ng_model_select.dart

@@ -42,19 +42,33 @@ class InputSelect implements AttachAware {
   }
 
   attach() {
+    singleSelectMode() {
+      _model.watchCollection = false;
+      _mode = new _SingleSelectMode(expando, _selectElement, _model, _nullOption, _unknownOption);
+      _scope.rootScope.domRead(() {
+        _mode.onModelChange(_model.viewValue);
+      });
+    }
+
+    multiSelectMode() {
+      _model.watchCollection = true;
+      _mode = new _MultipleSelectionMode(expando, _selectElement, _model);
+      _scope.rootScope.domRead(() {
+        _mode.onModelChange(_model.viewValue);
+      });
+    }
+
+    if (!_selectElement.attributes.containsKey('multiple')) {
+      singleSelectMode();
+    }
+
     _attrs.observe('multiple', (value) {
       _mode.destroy();
-      if (value == null) {
-        _model.watchCollection = false;
-        _mode = new _SingleSelectMode(expando, _selectElement, _model,
-            _nullOption, _unknownOption);
+      if (value == null || value != '') {
+        multiSelectMode();
       } else {
-        _model.watchCollection = true;
-        _mode = new _MultipleSelectionMode(expando, _selectElement, _model);
+        singleSelectMode();
       }
-      _scope.rootScope.domRead(() {
-        _mode.onModelChange(_model.viewValue);
-      });
     });
 
     _selectElement.onChange.listen((event) => _mode.onViewChange(event));

lib/directive/ng_model_validators.dart

@@ -280,6 +280,7 @@ class NgModelMinLengthValidator implements NgValidator {
 
   NgModelMinLengthValidator(NgModel this._ngModel) {
     _ngModel.addValidator(this);
+    _minlength = 0;
   }
 
   bool isValid(modelValue) {

test/core_dom/directive_spec.dart

@@ -5,12 +5,12 @@ import '../_specs.dart';
 main() {
   describe('NodeAttrs', () {
     var element;
-    var nodeAttrs;
+    NodeAttrs nodeAttrs;
     TestBed _;
 
     beforeEach((TestBed tb) {
       _ = tb;
-      element = _.compile('<div foo="bar" foo-bar="baz" foo-bar-baz="foo"></div>');
+      element = _.compile('<div foo="bar" foo-bar="baz" foo-bar-baz="foo" cux></div>');
       nodeAttrs = new NodeAttrs(element);
     });
 
@@ -27,7 +27,7 @@ main() {
     it('should provide a forEach function to iterate over attributes', () {
       Map<String, String> attrMap = new Map();
       nodeAttrs.forEach((k, v) => attrMap[k] = v);
-      expect(attrMap).toEqual({'foo': 'bar', 'foo-bar': 'baz', 'foo-bar-baz': 'foo'});
+      expect(attrMap).toEqual({'foo': 'bar', 'foo-bar': 'baz', 'foo-bar-baz': 'foo', 'cux': ''});
     });
 
     it('should provide a contains method', () {
@@ -38,7 +38,34 @@ main() {
     });
 
     it('should return the attribute names', () {
-      expect(nodeAttrs.keys.toList()..sort()).toEqual(['foo', 'foo-bar', 'foo-bar-baz']);
+      expect(nodeAttrs.keys.toList()..sort()).toEqual(['cux', 'foo', 'foo-bar', 'foo-bar-baz']);
+    });
+
+    it('should not call function with argument set to null when observing a'
+        ' property', () {
+      var invoked;
+      nodeAttrs.observe("a", (arg) {
+        invoked = true;
+      });
+      expect(invoked).toBeFalsy();
+    });
+
+    it('should call function when argument is set when observing a property',
+        () {
+      var seenValue = '';
+      nodeAttrs.observe("foo", (arg) {
+        seenValue = arg;
+      });
+      expect(seenValue).toEqual('bar');
+    });
+
+    it('should call function with argument set to \'\' when observing a boolean attribute',
+        () {
+      var seenValue;
+      nodeAttrs.observe("cux", (arg) {
+        seenValue = arg;
+      });
+      expect(seenValue).toEqual('');
     });
   });
 }

test/directive/ng_form_spec.dart

@@ -710,6 +710,8 @@ void main() {
         Probe probe = s.context['i'];
         var model = probe.directive(NgModel);
 
+        _.rootScope.apply();
+
         expect(s.eval('name')).toEqual('cool');
         expect(s.eval('myForm.name')).toEqual('myForm');
         expect(s.eval('myForm["name"]')).toBe(model);