reverted:
--- b/core/lib/Drupal/Core/Validation/ConstraintManager.php
+++ a/core/lib/Drupal/Core/Validation/ConstraintManager.php
@@ -108,12 +108,6 @@
       'class' => '\Symfony\Component\Validator\Constraints\Email',
       'type' => array('string'),
     ));
-    // @todo Should this be turned into a plugin of ours ?
-    $this->discovery->setDefinition('Count', array(
-      'label' => t('Count'),
-      'class' => '\Symfony\Component\Validator\Constraints\Count',
-      'type' => array(),
-    ));
   }
 
   /**
diff -u b/core/modules/entity_reference/lib/Drupal/entity_reference/Type/ConfigurableEntityReferenceItem.php b/core/modules/entity_reference/lib/Drupal/entity_reference/Type/ConfigurableEntityReferenceItem.php
--- b/core/modules/entity_reference/lib/Drupal/entity_reference/Type/ConfigurableEntityReferenceItem.php
+++ b/core/modules/entity_reference/lib/Drupal/entity_reference/Type/ConfigurableEntityReferenceItem.php
@@ -99,7 +99,7 @@
    * since we cannot extend it.
    */
   public static function schema(Field $field) {
-    $definition = \Drupal::typedData()->getDefinition('field_type:' . $field->type);
+    $definition = \Drupal::typedData()->getDefinition('configurable_field_type:' . $field->type);
     $module = $definition['module'];
     module_load_install($module);
     $callback = "{$module}_field_schema";
diff -u b/core/modules/field/field.module b/core/modules/field/field.module
--- b/core/modules/field/field.module
+++ b/core/modules/field/field.module
@@ -235,7 +235,7 @@
 function field_data_type_info() {
   // Expose each "configurable field" type as a data type. We add one single
   // entry, which will be expanded through plugin derivatives.
-  $items['field_type'] = array(
+  $items['configurable_field_type'] = array(
     'derivative' => '\Drupal\field\Plugin\DataType\ConfigFieldDataTypeDerivative',
   );
   return $items;
@@ -322,7 +322,7 @@
   $definition = array(
     'label' => t('Field !name', array('!name' => $field->id())),
     // @todo change the prefix to 'configurable something'.
-    'type' => 'field_type:' . $field->type,
+    'type' => 'configurable_field_type:' . $field->type,
     'list' => TRUE,
     'configurable' => TRUE,
     'translatable' => !empty($field->translatable),
diff -u b/core/modules/field/lib/Drupal/field/Plugin/Type/FieldType/ConfigFieldItemBase.php b/core/modules/field/lib/Drupal/field/Plugin/Type/FieldType/ConfigFieldItemBase.php
--- b/core/modules/field/lib/Drupal/field/Plugin/Type/FieldType/ConfigFieldItemBase.php
+++ b/core/modules/field/lib/Drupal/field/Plugin/Type/FieldType/ConfigFieldItemBase.php
@@ -9,8 +9,7 @@
 
 use Drupal\Core\Entity\Field\FieldItemBase;
 use Drupal\Core\TypedData\TypedDataInterface;
-use Drupal\field\Plugin\Core\Entity\Field;
-use Drupal\field\Field as FieldAPI;
+use Drupal\field\Field;
 
 /**
  * Base class for 'configurable field type' plugin implementations.
@@ -34,7 +33,7 @@
     }
     else {
       $entity = $parent->getParent();
-      $instances = FieldAPI::fieldInfo()->getBundleInstances($entity->entityType(), $entity->bundle());
+      $instances = Field::fieldInfo()->getBundleInstances($entity->entityType(), $entity->bundle());
       $this->instance = $instances[$parent->name];
     }
   }
diff -u b/core/modules/field/lib/Drupal/field/Plugin/Type/Widget/WidgetBase.php b/core/modules/field/lib/Drupal/field/Plugin/Type/Widget/WidgetBase.php
--- b/core/modules/field/lib/Drupal/field/Plugin/Type/Widget/WidgetBase.php
+++ b/core/modules/field/lib/Drupal/field/Plugin/Type/Widget/WidgetBase.php
@@ -377,25 +377,9 @@
 
         $violations_by_delta = array();
         foreach ($field_state['constraint_violations'] as $violation) {
-          // @todo Hackish - how do we make that better ?
-          if ($violation->getPropertyPath()) {
-            $property_path = explode('.', $violation->getPropertyPath());
-            // @todo See https://drupal.org/node/2012682 - base constraints
-            // violations come with a propertyPath that doesn't contain the delta.
-            // For now, assign to delta 0.
-            if (is_numeric($property_path[0])) {
-              $delta = array_shift($property_path);
-            }
-            else {
-              $delta = 0;
-            }
-          }
-          else {
-            // For case like "max number of values"...
-            // @todo Hackish too...
-            $property_path = array(key($this->field->getColumns()));
-            $delta = 0;
-          }
+          // Separate violations by delta.
+          $property_path = explode('.', $violation->getPropertyPath());
+          $delta = array_shift($property_path);
           $violation->arrayPropertyPath = $property_path;
           $violations_by_delta[$delta][] = $violation;
         }
@@ -411,6 +395,7 @@
             $delta_element = $element[$original_delta];
           }
           foreach ($delta_violations as $violation) {
+            // @todo: Pass $violation->arrayPropertyPath as property path.
             $error_element = $this->errorElement($delta_element, $violation, $form, $form_state);
             form_error($error_element, $violation->getMessage());
           }
diff -u b/core/modules/system/lib/Drupal/system/Tests/Entity/EntityFieldTest.php b/core/modules/system/lib/Drupal/system/Tests/Entity/EntityFieldTest.php
--- b/core/modules/system/lib/Drupal/system/Tests/Entity/EntityFieldTest.php
+++ b/core/modules/system/lib/Drupal/system/Tests/Entity/EntityFieldTest.php
@@ -362,7 +362,7 @@
     $definitions = $wrapped_entity->getPropertyDefinitions($definition);
     $this->assertEqual($definitions['name']['type'], 'string_field', $entity_type .': Name field found.');
     $this->assertEqual($definitions['user_id']['type'], 'entity_reference_field', $entity_type .': User field found.');
-    $this->assertEqual($definitions['field_test_text']['type'], 'field_type:text', $entity_type .': Test-text-field field found.');
+    $this->assertEqual($definitions['field_test_text']['type'], 'configurable_field_type:text', $entity_type .': Test-text-field field found.');
 
     // Test introspecting an entity object.
     // @todo: Add bundles and test bundles as well.
@@ -371,7 +371,7 @@
     $definitions = $entity->getPropertyDefinitions();
     $this->assertEqual($definitions['name']['type'], 'string_field', $entity_type .': Name field found.');
     $this->assertEqual($definitions['user_id']['type'], 'entity_reference_field', $entity_type .': User field found.');
-    $this->assertEqual($definitions['field_test_text']['type'], 'field_type:text', $entity_type .': Test-text-field field found.');
+    $this->assertEqual($definitions['field_test_text']['type'], 'configurable_field_type:text', $entity_type .': Test-text-field field found.');
 
     $name_properties = $entity->name->getPropertyDefinitions();
     $this->assertEqual($name_properties['value']['type'], 'string', $entity_type .': String value property of the name found.');
diff -u b/core/modules/system/lib/Drupal/system/Tests/TypedData/TypedDataTest.php b/core/modules/system/lib/Drupal/system/Tests/TypedData/TypedDataTest.php
--- b/core/modules/system/lib/Drupal/system/Tests/TypedData/TypedDataTest.php
+++ b/core/modules/system/lib/Drupal/system/Tests/TypedData/TypedDataTest.php
@@ -7,6 +7,7 @@
 
 namespace Drupal\system\Tests\TypedData;
 
+use Drupal\Component\Utility\String;
 use Drupal\simpletest\DrupalUnitTestBase;
 use Drupal\Core\Datetime\DrupalDateTime;
 use DateInterval;
@@ -549,4 +550,18 @@
     $violations = $this->typedData->create($definition, 0)->validate();
     $this->assertEqual($violations->count(), 0);
+
+    // Test validating a list of a values and make sure property paths starting
+    // with "0" are created.
+    $definition = array(
+      'type' => 'integer_field',
+      'list' => TRUE,
+    );
+    $violations = $this->typedData->create($definition, array(array('value' => 10)))->validate();
+    $this->assertEqual($violations->count(), 0);
+    $violations = $this->typedData->create($definition, array(array('value' => 'string')))->validate();
+    $this->assertEqual($violations->count(), 1);
+
+    $this->assertEqual($violations[0]->getInvalidValue(), 'string');
+    $this->assertIdentical($violations[0]->getPropertyPath(), '0.value');
   }
 }
only in patch2:
unchanged:
--- a/core/lib/Drupal/Core/TypedData/Validation/PropertyContainerMetadata.php
+++ b/core/lib/Drupal/Core/TypedData/Validation/PropertyContainerMetadata.php
@@ -28,7 +28,7 @@ public function accept(ValidationVisitorInterface $visitor, $typed_data, $group,
       $typed_data = NULL;
     }
     $visitor->visit($this, $typed_data, $group, $propertyPath);
-    $pathPrefix = empty($propertyPath) ? '' : $propertyPath . '.';
+    $pathPrefix = isset($propertyPath) && $propertyPath !== '' ? $propertyPath . '.' : '';
 
     if ($typed_data) {
       foreach ($typed_data as $name => $data) {
only in patch2:
unchanged:
--- /dev/null
+++ b/core/lib/Drupal/Core/Validation/Plugin/Validation/Constraint/CountConstraint.php
@@ -0,0 +1,37 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\Validation\Plugin\Validation\Constraint\CountConstraint.
+ */
+
+namespace Drupal\Core\Validation\Plugin\Validation\Constraint;
+
+use Drupal\Component\Annotation\Plugin;
+use Drupal\Core\Annotation\Translation;
+use Symfony\Component\Validator\Constraints\Count;
+
+/**
+ * Count constraint.
+ *
+ * Overrides the symfony constraint to use Drupal-style replacement patterns.
+ *
+ * @Plugin(
+ *   id = "Count",
+ *   label = @Translation("Count", context = "Validation"),
+ *   type = { "list" }
+ * )
+ */
+class CountConstraint extends Count {
+
+  public $minMessage = 'This collection should contain %limit element or more.|This collection should contain %limit elements or more.';
+  public $maxMessage = 'This collection should contain %limit element or less.|This collection should contain %limit elements or less.';
+  public $exactMessage = 'This collection should contain exactly %limit element.|This collection should contain exactly %limit elements.';
+
+  /**
+   * Overrides Range::validatedBy().
+   */
+  public function validatedBy() {
+    return '\Symfony\Component\Validator\Constraints\CountValidator';
+  }
+}