reverted:
--- b/core/modules/migrate/lib/Drupal/migrate/DrupalMessage.php
+++ /dev/null
@@ -1,15 +0,0 @@
-<?php
-
-/**
- * @file
- * Contains \Drupal\migrate\DrupalMessage.
- */
-
-namespace Drupal\migrate;
-
-class DrupalMessage implements MigrateMessageInterface {
-
-  function display($message, $type = 'status') {
-    drupal_set_message($message, $type);
-  }
-}
diff -u b/core/modules/migrate/lib/Drupal/migrate/MigrateException.php b/core/modules/migrate/lib/Drupal/migrate/MigrateException.php
--- b/core/modules/migrate/lib/Drupal/migrate/MigrateException.php
+++ b/core/modules/migrate/lib/Drupal/migrate/MigrateException.php
@@ -16,6 +16,10 @@
    * @var int
    */
   protected $level;
+
+  /**
+   * @return int
+   */
   public function getLevel() {
     return $this->level;
   }
diff -u b/core/modules/migrate/lib/Drupal/migrate/MigrateExecutable.php b/core/modules/migrate/lib/Drupal/migrate/MigrateExecutable.php
--- b/core/modules/migrate/lib/Drupal/migrate/MigrateExecutable.php
+++ b/core/modules/migrate/lib/Drupal/migrate/MigrateExecutable.php
@@ -59,8 +59,18 @@
    * @var array
    */
   protected $sourceIdValues;
+
+  /**
+   * @var int
+   */
   protected $processed_since_feedback = 0;
 
+  /**
+   * @param MigrationInterface $migration
+   * @param MigrateMessageInterface $message
+   *
+   * @throws \Drupal\migrate\MigrateException
+   */
   public function __construct(MigrationInterface $migration, MigrateMessageInterface $message) {
     $this->migration = $migration;
     $this->message = $message;
@@ -82,7 +92,7 @@
             $limit *= 1024;
             break;
           default:
-            throw new \Exception(t('Invalid PHP memory_limit !limit',
+            throw new MigrateException(t('Invalid PHP memory_limit !limit',
               array('!limit' => $limit)));
         }
       }
@@ -95,7 +105,7 @@
    */
   public function getSource() {
     if (!isset($this->source)) {
-      $this->source = new Source($this->migration);
+      $this->source = new Source($this->migration, $this);
     }
     return $this->source;
   }
@@ -165,12 +175,12 @@
       try {
         $destination_id_values = $destination->import($row);
         if ($destination_id_values) {
-          $id_map->saveIDMapping($row, $destination_id_values, $this->needsUpdate, $this->rollbackAction);
+          $id_map->saveIdMapping($row, $destination_id_values, $this->needsUpdate, $this->rollbackAction);
           $this->successes_since_feedback++;
           $this->total_successes++;
         }
         else {
-          $id_map->saveIDMapping($row, array(), MigrateIdMapInterface::STATUS_FAILED, $this->rollbackAction);
+          $id_map->saveIdMapping($row, array(), MigrateIdMapInterface::STATUS_FAILED, $this->rollbackAction);
           if ($id_map->messageCount() == 0) {
             $message = t('New object was not saved, no error provided');
             $this->saveMessage($message);
@@ -178,13 +188,13 @@
           }
         }
       }
-      catch (\MigrateException $e) {
-        $this->migration->getIdMap()->saveIDMapping($row, array(), $e->getStatus(), $this->rollbackAction);
+      catch (MigrateException $e) {
+        $this->migration->getIdMap()->saveIdMapping($row, array(), $e->getStatus(), $this->rollbackAction);
         $this->saveMessage($e->getMessage(), $e->getLevel());
         $this->message->display($e->getMessage());
       }
       catch (\Exception $e) {
-        $this->migration->getIdMap()->saveIDMapping($row, array(), MigrateIdMapInterface::STATUS_FAILED, $this->rollbackAction);
+        $this->migration->getIdMap()->saveIdMapping($row, array(), MigrateIdMapInterface::STATUS_FAILED, $this->rollbackAction);
         $this->handleException($e);
       }
       $this->total_processed++;
diff -u b/core/modules/migrate/lib/Drupal/migrate/MigrateMessageInterface.php b/core/modules/migrate/lib/Drupal/migrate/MigrateMessageInterface.php
--- b/core/modules/migrate/lib/Drupal/migrate/MigrateMessageInterface.php
+++ b/core/modules/migrate/lib/Drupal/migrate/MigrateMessageInterface.php
@@ -10,4 +10,10 @@
 interface MigrateMessageInterface {
 
+  /**
+   * @param $message
+   * @param string $type
+   *
+   * @return mixed
+   */
   function display($message, $type = 'status');
 }
diff -u b/core/modules/migrate/lib/Drupal/migrate/Plugin/MigrateIdMapInterface.php b/core/modules/migrate/lib/Drupal/migrate/Plugin/MigrateIdMapInterface.php
--- b/core/modules/migrate/lib/Drupal/migrate/Plugin/MigrateIdMapInterface.php
+++ b/core/modules/migrate/lib/Drupal/migrate/Plugin/MigrateIdMapInterface.php
@@ -45,7 +45,7 @@
    * @param $status
    * @param $rollback_action
    */
-  public function saveIDMapping(Row $row, array $destination_id_values, $status = self::STATUS_IMPORTED, $rollback_action = self::ROLLBACK_DELETE);
+  public function saveIdMapping(Row $row, array $destination_id_values, $status = self::STATUS_IMPORTED, $rollback_action = self::ROLLBACK_DELETE);
 
   /**
    * Record a message related to a source record
@@ -89,6 +89,7 @@
    * Delete the map and message entries for a given source record
    *
    * @param array $source_key
+   * @param bool $messages_only
    */
   public function delete(array $source_key, $messages_only = FALSE);
 
@@ -115,7 +116,16 @@
    * Retrieve map data for a given source or destination item
    */
   public function getRowBySource(array $source_id);
-  public function getRowByDestination(array $destination_id);
+
+
+  /**
+   * Retrieve a row by the destination identifiers.
+   *
+   * @param array $destination_id
+   *
+   * @return array
+   */
+  public function getRowByDestination(array $destination_id_values);
 
   /**
    * Retrieve an array of map rows marked as needing update.
diff -u b/core/modules/migrate/lib/Drupal/migrate/Plugin/MigrateProcessBag.php b/core/modules/migrate/lib/Drupal/migrate/Plugin/MigrateProcessBag.php
--- b/core/modules/migrate/lib/Drupal/migrate/Plugin/MigrateProcessBag.php
+++ b/core/modules/migrate/lib/Drupal/migrate/Plugin/MigrateProcessBag.php
@@ -21,6 +21,11 @@
 
   protected $pluginKey = 'plugin';
 
+  /**
+   * @param PluginManagerInterface $manager
+   * @param array $configurations
+   * @param MigrationInterface $migration
+   */
   public function __construct(PluginManagerInterface $manager, array $configurations = array(), MigrationInterface $migration) {
     parent::__construct($manager, $configurations);
     $this->migration = $migration;
diff -u b/core/modules/migrate/lib/Drupal/migrate/Plugin/migrate/destination/Config.php b/core/modules/migrate/lib/Drupal/migrate/Plugin/migrate/destination/Config.php
--- b/core/modules/migrate/lib/Drupal/migrate/Plugin/migrate/destination/Config.php
+++ b/core/modules/migrate/lib/Drupal/migrate/Plugin/migrate/destination/Config.php
@@ -10,6 +10,7 @@
 use Drupal\Core\Plugin\ContainerFactoryPluginInterface;
 use Drupal\migrate\Entity\Migration;
 use Drupal\migrate\Entity\MigrationInterface;
+use Drupal\migrate\MigrateException;
 use Drupal\migrate\Row;
 use Symfony\Component\DependencyInjection\ContainerInterface;
 use Drupal\Core\Config\Config as ConfigObject;
@@ -28,6 +29,12 @@
    */
   protected $config;
 
+  /**
+   * @param array $configuration
+   * @param string $plugin_id
+   * @param array $plugin_definition
+   * @param ConfigObject $config
+   */
   public function __construct(array $configuration, $plugin_id, array $plugin_definition, ConfigObject $config) {
     parent::__construct($configuration, $plugin_id, $plugin_definition);
     $this->config = $config;
@@ -51,10 +58,27 @@
       ->save();
   }
 
+  /**
+   * @param array $destination_keys
+   *
+   * @throws \Drupal\migrate\MigrateException
+   */
   public function rollbackMultiple(array $destination_keys) {
-    throw new \MigrateException('Configuration can not be rolled back');
+    throw new MigrateException('Configuration can not be rolled back');
   }
 
+  /**
+   * Derived classes must implement fields(), returning a list of available
+   * destination fields.
+   *
+   * @todo Review the cases where we need the Migration parameter, can we avoid that?
+   *
+   * @param Migration $migration
+   *   Optionally, the migration containing this destination.
+   * @return array
+   *  - Keys: machine names of the fields
+   *  - Values: Human-friendly descriptions of the fields.
+   */
   public function fields(Migration $migration = NULL) {
     // @todo Dynamically fetch fields using Config Schema API.
   }
diff -u b/core/modules/migrate/lib/Drupal/migrate/Plugin/migrate/id_map/Sql.php b/core/modules/migrate/lib/Drupal/migrate/Plugin/migrate/id_map/Sql.php
--- b/core/modules/migrate/lib/Drupal/migrate/Plugin/migrate/id_map/Sql.php
+++ b/core/modules/migrate/lib/Drupal/migrate/Plugin/migrate/id_map/Sql.php
@@ -54,6 +54,15 @@
    */
   protected $migration;
 
+  /**
+   * @var array
+   */
+  protected $sourceIdFields;
+
+  /**
+   * @var array
+   */
+  protected $destinationIdFields;
 
   /**
    * Qualifying the map table name with the database name makes cross-db joins
@@ -98,15 +107,15 @@
     $this->destinationIds = $migration->get('destinationIds');
 
     // Build the source and destination key maps
-    $this->sourceKeyMap = array();
+    $this->sourceIdFields = array();
     $count = 1;
     foreach ($this->sourceIds as $field => $schema) {
-      $this->sourceKeyMap[$field] = 'sourceid' . $count++;
+      $this->sourceIdFields[$field] = 'sourceid' . $count++;
     }
-    $this->destinationKeyMap = array();
+    $this->destinationIdFields = array();
     $count = 1;
     foreach ($this->destinationIds as $field => $schema) {
-      $this->destinationKeyMap[$field] = 'destid' . $count++;
+      $this->destinationIdFields[$field] = 'destid' . $count++;
     }
     $this->ensureTables();
   }
@@ -250,7 +259,7 @@
   public function getRowBySource(array $source_id) {
     $query = $this->getDatabase()->select($this->mapTable, 'map')
               ->fields('map');
-    foreach ($this->sourceKeyMap as $key_name) {
+    foreach ($this->sourceIdFields as $key_name) {
       $query = $query->condition("map.$key_name", array_shift($source_id), '=');
     }
     $result = $query->execute();
@@ -260,12 +269,15 @@
   /**
    * Retrieve a row from the map table, given a destination ID
    *
-   * @param array $source_id
+   * @param array $destination_id
+   *
+   * @return mixed
+   *   The row(s) of data
    */
   public function getRowByDestination(array $destination_id) {
     $query = $this->getDatabase()->select($this->mapTable, 'map')
               ->fields('map');
-    foreach ($this->destinationKeyMap as $key_name) {
+    foreach ($this->destinationIdFields as $key_name) {
       $query = $query->condition("map.$key_name", array_shift($destination_id), '=');
     }
     $result = $query->execute();
@@ -304,8 +316,8 @@
    */
   public function lookupSourceID(array $destination_id) {
     $query = $this->getDatabase()->select($this->mapTable, 'map')
-              ->fields('map', $this->sourceKeyMap);
-    foreach ($this->destinationKeyMap as $key_name) {
+              ->fields('map', $this->sourceIdFields);
+    foreach ($this->destinationIdFields as $key_name) {
       $query = $query->condition("map.$key_name", array_shift($destination_id), '=');
     }
     $result = $query->execute();
@@ -324,8 +336,8 @@
    */
   public function lookupDestinationID(array $source_id) {
     $query = $this->getDatabase()->select($this->mapTable, 'map')
-              ->fields('map', $this->destinationKeyMap);
-    foreach ($this->sourceKeyMap as $key_name) {
+              ->fields('map', $this->destinationIdFields);
+    foreach ($this->sourceIdFields as $key_name) {
       $query = $query->condition("map.$key_name", array_shift($source_id), '=');
     }
     $result = $query->execute();
@@ -338,7 +350,7 @@
    * to the destination key. Also may be called, setting the third parameter to
    * NEEDS_UPDATE, to signal an existing record should be remigrated.
    *
-   * @param stdClass $row
+   * @param Row $row
    *  The raw source data. We use the key map derived from the source object
    *  to get the source key values.
    * @param array $dest_ids
@@ -351,11 +363,11 @@
    * $param string $hash
    *  If hashing is enabled, the hash of the raw source row.
    */
-  public function saveIDMapping(Row $row, array $destination_id_values, $needs_update = MigrateIdMapInterface::STATUS_IMPORTED, $rollback_action = MigrateIdMapInterface::ROLLBACK_DELETE) {
+  public function saveIdMapping(Row $row, array $destination_id_values, $needs_update = MigrateIdMapInterface::STATUS_IMPORTED, $rollback_action = MigrateIdMapInterface::ROLLBACK_DELETE) {
     // Construct the source key
     $keys = array();
     $destination = $row->getDestination();
-    foreach ($this->sourceKeyMap as $field_name => $key_name) {
+    foreach ($this->sourceIdFields as $field_name => $key_name) {
       // A NULL key value will fail.
       if (!isset($destination[$field_name])) {
         $this->message->display(t(
@@ -619,10 +631,10 @@
   public function rewind() {
     $this->currentRow = NULL;
     $fields = array();
-    foreach ($this->sourceKeyMap as $field) {
+    foreach ($this->sourceIdFields as $field) {
       $fields[] = $field;
     }
-    foreach ($this->destinationKeyMap as $field) {
+    foreach ($this->destinationIdFields as $field) {
       $fields[] = $field;
     }
 
@@ -665,7 +677,7 @@
       $this->currentRow = NULL;
     }
     else {
-      foreach ($this->sourceKeyMap as $map_field) {
+      foreach ($this->sourceIdFields as $map_field) {
         $this->currentKey[$map_field] = $this->currentRow->$map_field;
         // Leave only destination fields
         unset($this->currentRow->$map_field);
diff -u b/core/modules/migrate/lib/Drupal/migrate/Plugin/migrate/source/D6Variable.php b/core/modules/migrate/lib/Drupal/migrate/Plugin/migrate/source/D6Variable.php
--- b/core/modules/migrate/lib/Drupal/migrate/Plugin/migrate/source/D6Variable.php
+++ b/core/modules/migrate/lib/Drupal/migrate/Plugin/migrate/source/D6Variable.php
@@ -24,6 +24,9 @@
    */
   protected $variables;
 
+  /**
+   * {@inheritdoc}
+   */
   function __construct(array $configuration, $plugin_id, array $plugin_definition, MigrationInterface $migration) {
     parent::__construct($configuration, $plugin_id, $plugin_definition, $migration);
     $this->variables = $this->configuration['variables'];
diff -u b/core/modules/migrate/lib/Drupal/migrate/Source.php b/core/modules/migrate/lib/Drupal/migrate/Source.php
--- b/core/modules/migrate/lib/Drupal/migrate/Source.php
+++ b/core/modules/migrate/lib/Drupal/migrate/Source.php
@@ -8,6 +8,7 @@
 namespace Drupal\migrate;
 
 use Drupal\migrate\Entity\MigrationInterface;
+use Drupal\migrate\Plugin\MigrateIdMapInterface;
 
 /**
  * A base class for migrate sources.
@@ -182,8 +183,9 @@
    *
    * @param \Drupal\migrate\Entity\MigrationInterface $migration
    */
-  function __construct(MigrationInterface $migration) {
+  function __construct(MigrationInterface $migration, MigrateExecutable $migrate_executable) {
     $this->migration = $migration;
+    $this->migrateExecutable = $migrate_executable;
     $configuration = $migration->get('source');
     if (!empty($configuration['cache_counts'])) {
       $this->cacheCounts = TRUE;
@@ -385,10 +387,10 @@
     if ($this->migration->getSource()->prepareRow($row) === FALSE) {
       // Make sure we replace any previous messages for this item with any
       // new ones.
-      $this->migration->getIdMap()->delete($this->currentIds, TRUE);
-      $this->migration->saveQueuedMessages();
-      $this->migration->getIdMap()->saveIDMapping($row, array(),
-        \MigrateMap::STATUS_IGNORED, $this->migration->rollbackAction);
+      $id_map = $this->migration->getIdMap();
+      $id_map->delete($this->currentIds, TRUE);
+      $this->migrateExecutable->saveQueuedMessages();
+      $id_map->saveIdMapping($row, array(), MigrateIdMapInterface::STATUS_IGNORED, $this->migrateExecutable->rollbackAction);
       $this->numIgnored++;
       $this->currentRow = NULL;
       $this->currentIds = NULL;
diff -u b/core/modules/migrate/lib/Drupal/migrate/Tests/Dump/Drupal6SystemSite.php b/core/modules/migrate/lib/Drupal/migrate/Tests/Dump/Drupal6SystemSite.php
--- b/core/modules/migrate/lib/Drupal/migrate/Tests/Dump/Drupal6SystemSite.php
+++ b/core/modules/migrate/lib/Drupal/migrate/Tests/Dump/Drupal6SystemSite.php
@@ -4,8 +4,14 @@
 
 use Drupal\Core\Database\Connection;
 
+/**
+ * Database dump for testing system.site.yml migration.
+ */
 class Drupal6SystemSite {
 
+  /**
+   * @param \Drupal\Core\Database\Connection $database
+   */
   public static function load(Connection $database) {
     $database->schema()->createTable('variable', array(
       'fields' => array(
diff -u b/core/modules/migrate/lib/Drupal/migrate/Tests/MigrateSystemConfigsTest.php b/core/modules/migrate/lib/Drupal/migrate/Tests/MigrateSystemConfigsTest.php
--- b/core/modules/migrate/lib/Drupal/migrate/Tests/MigrateSystemConfigsTest.php
+++ b/core/modules/migrate/lib/Drupal/migrate/Tests/MigrateSystemConfigsTest.php
@@ -7,11 +7,14 @@
 
 namespace Drupal\migrate\Tests;
 
-use Drupal\migrate\DrupalMessage;
+use Drupal\migrate\MigrateMessage;
 use Drupal\migrate\MigrateExecutable;
 
 class MigrateSystemConfigsTest extends MigrateTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
   public static function getInfo() {
     return array(
       'name'  => 'Migrate variables to system.site.yml',
@@ -26,7 +29,7 @@
       drupal_get_path('module', 'migrate') . '/ib/Drupal/migrate/Tests/Dump/Drupal6SystemSite.php',
     );
     $this->prepare($migration, $dumps);
-    $executable = new MigrateExecutable($migration, new DrupalMessage);
+    $executable = new MigrateExecutable($migration, new MigrateMessage);
     $executable->import();
     $config = \Drupal::config('system.site');
     $this->assertIdentical($config->get('name'), 'drupal');
diff -u b/core/modules/migrate/lib/Drupal/migrate/Tests/MigrateTestBase.php b/core/modules/migrate/lib/Drupal/migrate/Tests/MigrateTestBase.php
--- b/core/modules/migrate/lib/Drupal/migrate/Tests/MigrateTestBase.php
+++ b/core/modules/migrate/lib/Drupal/migrate/Tests/MigrateTestBase.php
@@ -23,6 +23,12 @@
 
   public static $modules = array('migrate');
 
+  /**
+   * @param MigrationInterface $migration
+   * @param array $files
+   *
+   * @return \Drupal\Core\Database\Connection
+   */
   protected function prepare(MigrationInterface $migration, array $files = array()) {
     $databasePrefix = 'simpletest_m_' . mt_rand(1000, 1000000);
     $connection_info = Database::getConnectionInfo('default');
diff -u b/core/modules/migrate/tests/Drupal/migrate/Tests/FakeDatabaseSchema.php b/core/modules/migrate/tests/Drupal/migrate/Tests/FakeDatabaseSchema.php
--- b/core/modules/migrate/tests/Drupal/migrate/Tests/FakeDatabaseSchema.php
+++ b/core/modules/migrate/tests/Drupal/migrate/Tests/FakeDatabaseSchema.php
@@ -142,7 +142,7 @@
   }
 
   /**
-   * Provide meta information about this battery of tests.
+   * {@inheritdoc}
    */
   public static function getInfo() {
     return array(
diff -u b/core/modules/migrate/tests/Drupal/migrate/Tests/FakeSelect.php b/core/modules/migrate/tests/Drupal/migrate/Tests/FakeSelect.php
--- b/core/modules/migrate/tests/Drupal/migrate/Tests/FakeSelect.php
+++ b/core/modules/migrate/tests/Drupal/migrate/Tests/FakeSelect.php
@@ -289,6 +289,9 @@
    *
    * @return bool
    *   TRUE if the condition matches.
+   *
+   * @throws \Exception
+   *
    */
   protected function matchSingle(array $row, array $condition) {
     $field_info = $this->getFieldInfo($condition['field']);
@@ -527,7 +530,7 @@
   }
 
   /**
-   * Provide meta information about this battery of tests.
+   * {@inheritdoc}
    */
   public static function getInfo() {
     return array(
diff -u b/core/modules/migrate/tests/Drupal/migrate/Tests/MigrateSqlSourceTestCase.php b/core/modules/migrate/tests/Drupal/migrate/Tests/MigrateSqlSourceTestCase.php
--- b/core/modules/migrate/tests/Drupal/migrate/Tests/MigrateSqlSourceTestCase.php
+++ b/core/modules/migrate/tests/Drupal/migrate/Tests/MigrateSqlSourceTestCase.php
@@ -60,7 +60,10 @@
     $migration->expects($this->any())
       ->method('getSource')
       ->will($this->returnValue($plugin));
-    $this->source = new Source($migration);
+    $migrateExecutable = $this->getMockBuilder('Drupal\migrate\MigrateExecutable')
+      ->disableOriginalConstructor()
+      ->getMock();
+    $this->source = new Source($migration, $migrateExecutable);
 
     $cache = $this->getMock('Drupal\Core\Cache\CacheBackendInterface');
     $this->writeAttribute($this->source, 'cache', $cache);
diff -u b/core/modules/migrate/tests/Drupal/migrate/Tests/MigrateTestCase.php b/core/modules/migrate/tests/Drupal/migrate/Tests/MigrateTestCase.php
--- b/core/modules/migrate/tests/Drupal/migrate/Tests/MigrateTestCase.php
+++ b/core/modules/migrate/tests/Drupal/migrate/Tests/MigrateTestCase.php
@@ -26,7 +26,7 @@
   /**
    * Retrieve a mocked migration.
    *
-   * @return \PHPUnit_Framework_MockObject_MockObject
+   * @return \Drupal\migrate\Entity\MigrationInterface
    *   The mocked migration.
    */
   protected function getMigration() {