make paper-form work with non contextual paper-inputs

addon/mixins/child-mixin.js

@@ -1,7 +1,17 @@
 import Ember from 'ember';
-const { Mixin } = Ember;
+import ParentMixin from 'ember-paper/mixins/parent-mixin';
+const { Mixin, computed } = Ember;
 
 export default Mixin.create({
+
+  // override to look for a specific parent class
+  parentClass: ParentMixin,
+
+  // this will typically be overriden when yielding a contextual component
+  parentComponent: computed(function() {
+    return this.nearestOfType(this.get('parentClass'));
+  }),
+
   init() {
     this._super(...arguments);
     if (this.get('parentComponent')) {
@@ -15,4 +25,4 @@ export default Mixin.create({
       this.get('parentComponent').unregister(this);
     }
   }
-});
+});

tests/integration/components/paper-form-test.js

@@ -107,4 +107,37 @@ test('form is reset after submit action is invoked', function(assert) {
   this.$('button').click();
 
   assert.equal(this.$('.ng-dirty').length, 0, 'inputs were reset');
-});
+});
+
+test('works without using contextual components', function(assert) {
+  assert.expect(4);
+
+  this.render(hbs`
+    {{#paper-form as |form|}}
+      {{paper-input value=foo onChange=(action (mut foo)) label="Foo"}}
+      {{paper-input value=bar onChange=(action (mut bar)) label="Bar" errors=errors}}
+
+      {{#if form.isInvalid}}
+        <div class="invalid-div">Form is invalid!</div>
+      {{/if}}
+      {{#if form.isValid}}
+        <div class="valid-div">Form is valid!</div>
+      {{/if}}
+
+    {{/paper-form}}
+  `);
+
+  assert.equal(this.$('.invalid-div').length, 0);
+  assert.equal(this.$('.valid-div').length, 1);
+
+  this.set('errors', [{
+    message: 'foo should be a number.',
+    attribute: 'foo'
+  }, {
+    message: 'foo should be smaller than 12.',
+    attribute: 'foo'
+  }]);
+
+  assert.equal(this.$('.invalid-div').length, 1);
+  assert.equal(this.$('.valid-div').length, 0);
+});