Added initial Migrate Preview module.

modules/migrate_preview/migrate_preview.info.yml

@@ -0,0 +1,8 @@
+name: 'Migrate preview'
+description: 'Displays a preview of a migration.'
+core: 8.x
+type: module
+package: 'Migration'
+dependencies:
+  - drupal:migrate
+  - migrate_tools:migrate_tools

modules/migrate_preview/migrate_preview.links.task.yml

@@ -0,0 +1,5 @@
+entity.migration.overview_preview:
+  title: Preview
+  route_name: entity.migration.preview
+  parent_id: entity.migration.overview
+  weight: 2.5

modules/migrate_preview/migrate_preview.routing.yml

@@ -0,0 +1,14 @@
+entity.migration.preview:
+  path: '/admin/structure/migrate/manage/{migration_group}/migrations/{migration}/preview'
+  defaults:
+    _controller: '\Drupal\migrate_preview\Controller\MigrationController::preview'
+    _title: 'Preview'
+    _migrate_group: true
+  requirements:
+    _permission: 'administer migrations'
+  options:
+    parameters:
+      migration:
+        type: entity:migration
+      migration_group:
+        type: entity:migration_group

modules/migrate_preview/src/Controller/MigrationController.php

@@ -0,0 +1,195 @@
+<?php
+
+namespace Drupal\migrate_preview\Controller;
+
+use Drupal\Component\Utility\Html;
+use Drupal\Component\Utility\Xss;
+use Drupal\Core\Controller\ControllerBase;
+use Drupal\Core\DependencyInjection\ContainerInjectionInterface;
+use Drupal\Core\Routing\CurrentRouteMatch;
+use Drupal\migrate\MigrateMessage;
+use Drupal\migrate\Plugin\MigrationPluginManagerInterface;
+use Drupal\migrate_plus\Entity\MigrationGroupInterface;
+use Drupal\migrate_plus\Entity\MigrationInterface;
+use Drupal\migrate_preview\MigratePreviewExecutable;
+use Symfony\Component\DependencyInjection\ContainerInterface;
+
+/**
+ * Returns responses for migrate_tools migration view routes.
+ */
+class MigrationController extends ControllerBase implements ContainerInjectionInterface {
+
+  /**
+   * Plugin manager for migration plugins.
+   *
+   * @var \Drupal\migrate\Plugin\MigrationPluginManagerInterface
+   */
+  protected $migrationPluginManager;
+
+  /**
+   * The current route match.
+   *
+   * @var \Drupal\Core\Routing\CurrentRouteMatch
+   */
+  protected $currentRouteMatch;
+
+  /**
+   * Constructs a new MigrationController object.
+   *
+   * @param \Drupal\migrate\Plugin\MigrationPluginManagerInterface $migration_plugin_manager
+   *   The plugin manager for config entity-based migrations.
+   * @param \Drupal\Core\Routing\CurrentRouteMatch $currentRouteMatch
+   *   The current route match.
+   */
+  public function __construct(MigrationPluginManagerInterface $migration_plugin_manager, CurrentRouteMatch $currentRouteMatch) {
+    $this->migrationPluginManager = $migration_plugin_manager;
+    $this->currentRouteMatch = $currentRouteMatch;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function create(ContainerInterface $container) {
+    return new static(
+      $container->get('plugin.manager.migration'),
+      $container->get('current_route_match')
+    );
+  }
+
+  /**
+   * Displays a preview of the source.
+   *
+   * @param \Drupal\migrate_plus\Entity\MigrationGroupInterface $migration_group
+   *   The migration group.
+   * @param \Drupal\migrate_plus\Entity\MigrationInterface $migration
+   *   The $migration.
+   *
+   * @return array
+   *   A render array as expected by drupal_render().
+   */
+  public function preview(MigrationGroupInterface $migration_group, MigrationInterface $migration) {
+    $migration_plugin = $this->migrationPluginManager->createInstance($migration->id(), $migration->toArray());
+    $migrateMessage = new MigrateMessage();
+    $executable = new MigratePreviewExecutable($migration_plugin, $migrateMessage, [
+      'limit' => 10,
+      'update' => TRUE,
+      'force' => TRUE,
+    ]);
+
+    // Compose header.
+    $header = [];
+    $source = $migration_plugin->getSourcePlugin();
+    foreach ($source->fields($migration_plugin) as $machine_name => $description) {
+      $header[$machine_name] = Xss::filterAdmin($description);
+    }
+
+    $migrate_rows = $executable->preview();
+    return [
+      'source' => $this->buildTable($header, $migrate_rows, 'source'),
+      'destination' => $this->buildTable($header, $migrate_rows, 'destination'),
+    ];
+  }
+
+  /**
+   * Builds a table from the given result.
+   *
+   * @param array $headers
+   *   The expected headers.
+   * @param \Drupal\migrate\Row[] $migrate_rows
+   *   A list of migrate rows.
+   *
+   * @return array
+   *   The rows for in the table.
+   */
+  protected function buildTable(array $headers, array $migrate_rows, $method = 'source') {
+    if (empty($migrate_rows)) {
+      return [
+        '#plain_text' => $this->t('No data.'),
+      ];
+    }
+
+    // Add keys from first item as additional headers.
+    switch ($method) {
+      case 'source':
+        $item = reset($migrate_rows)->getSource();
+        break;
+
+      case 'destination':
+        $item = reset($migrate_rows)->getRawDestination();
+        break;
+    }
+    $keys = array_merge(array_keys($headers), array_keys($item));
+    foreach (array_keys($item) as $key) {
+      if (!isset($headers[$key])) {
+        $headers[$key] = Xss::filterAdmin($key);
+      }
+    }
+
+    $rows = [];
+    $index = 0;
+    foreach ($migrate_rows as $migrate_row) {
+      switch ($method) {
+        case 'source':
+          $row = $migrate_row->getSource();
+          break;
+
+        case 'destination':
+          $row = $migrate_row->getRawDestination();
+          break;
+      }
+      $row += array_fill_keys($keys, NULL);
+
+      foreach ($keys as $column) {
+        $rows[$index][$column] = $this->buildValue($row[$column]);
+      }
+
+      $index++;
+    }
+
+    return [
+      '#type' => 'container',
+      '#attributes' => [
+        'style' => 'overflow: scroll;',
+      ],
+      'table' => [
+        '#type' => 'table',
+        '#header' => $headers,
+      ] + $rows,
+    ];
+  }
+
+  protected function buildValue($value) {
+    $row_value = [
+      '#plain_text' => $value,
+    ];
+
+    if (is_string($value) && strlen($value) > 255) {
+      $value = substr($value, 0, 255) . '...';
+    }
+
+    if (is_scalar($value)) {
+      $row_value['#plain_text'] = $value;
+    }
+    elseif (is_array($value)) {
+      foreach ($value as $value_index => &$subvalue) {
+        if (is_string($subvalue)) {
+          if (strlen($subvalue) > 255) {
+            $subvalue = substr($subvalue, 0, 255) . '...';
+          }
+        }
+        if (!is_scalar($subvalue)) {
+          $subvalue = print_r($subvalue, TRUE);
+          $value[$value_index] = $this->buildValue($subvalue)['#plain_text'];
+        }
+      }
+
+      $row_value = [
+        '#theme' => 'item_list',
+        '#items' => $value,
+      ];
+    }
+
+    return $row_value;
+  }
+
+}

modules/migrate_preview/src/MigratePreviewExecutable.php

@@ -0,0 +1,128 @@
+<?php
+
+namespace Drupal\migrate_preview;
+
+use Drupal\migrate\Event\MigrateEvents;
+use Drupal\migrate\Event\MigrateImportEvent;
+use Drupal\migrate\Exception\RequirementsException;
+use Drupal\migrate\MigrateException;
+use Drupal\migrate\MigrateSkipRowException;
+use Drupal\migrate\Plugin\MigrationInterface;
+use Drupal\migrate_tools\MigrateExecutable as MigrateExecutableBase;
+
+/**
+ * Defines a migrate executable for previewing.
+ *
+ * @todo prevent a migration from changing status.
+ */
+class MigratePreviewExecutable extends MigrateExecutableBase {
+
+  /**
+   * Returns the source.
+   *
+   * Makes sure source is initialized based on migration settings.
+   *
+   * @return \Drupal\migrate\Plugin\MigrateSourceInterface
+   *   The source.
+   */
+  protected function getSource() {
+    if (!isset($this->source)) {
+      $this->source = $this->migration->getSourcePlugin();
+    }
+    return $this->source;
+  }
+
+  /**
+   * Get the ID map from the current migration.
+   *
+   * @return \Drupal\migrate\Plugin\MigrateIdMapInterface
+   *   The ID map.
+   */
+  protected function getIdMap() {
+    return $this->migration->getIdMap();
+  }
+
+  /**
+   *
+   */
+  public function preview() {
+    $this->getEventDispatcher()->dispatch(MigrateEvents::PRE_IMPORT, new MigrateImportEvent($this->migration, $this->message));
+
+    // Knock off migration if the requirements haven't been met.
+    try {
+      $this->migration->checkRequirements();
+    }
+    catch (RequirementsException $e) {
+      $this->message->display(
+        $this->t(
+          'Migration @id did not meet the requirements. @message @requirements',
+          [
+            '@id' => $this->migration->id(),
+            '@message' => $e->getMessage(),
+            '@requirements' => $e->getRequirementsString(),
+          ]
+        ),
+        'error'
+      );
+
+      return [];
+    }
+
+    $source = $this->getSource();
+    $id_map = $this->getIdMap();
+    $id_map->prepareUpdate();
+    $this->migration->set('requirements', []);
+
+    try {
+      $source->rewind();
+    }
+    catch (\Exception $e) {
+      $this->message->display(
+        $this->t('Migration failed with source plugin exception: @e', ['@e' => $e->getMessage()]), 'error');
+      return [];
+    }
+
+    $rows = [];
+    while ($source->valid()) {
+      $row = $source->current();
+      $this->sourceIdValues = $row->getSourceIdValues();
+
+      try {
+        $this->processRow($row);
+        $rows[] = $row;
+        $this->itemLimitCounter++;
+
+        if ($this->itemLimit && ($this->itemLimitCounter) >= $this->itemLimit) {
+          break;
+        }
+      }
+      catch (MigrateException $e) {
+        // @todo show message to user.
+        //$this->getIdMap()->saveIdMapping($row, [], $e->getStatus());
+        //$this->saveMessage($e->getMessage(), $e->getLevel());
+      }
+      catch (MigrateSkipRowException $e) {
+        // @todo show message to user.
+//        if ($e->getSaveToMap()) {
+//          $id_map->saveIdMapping($row, [], MigrateIdMapInterface::STATUS_IGNORED);
+//        }
+//        if ($message = trim($e->getMessage())) {
+//          $this->saveMessage($message, MigrationInterface::MESSAGE_INFORMATIONAL);
+//        }
+      }
+
+      try {
+        $source->next();
+      }
+      catch (\Exception $e) {
+        $this->message->display(
+          $this->t('Migration failed with source plugin exception: @e',
+            ['@e' => $e->getMessage()]), 'error');
+        return $rows;
+      }
+    }
+
+    return $rows;
+  }
+
+}