Allow a callback function for the Source path parameter.

src/Plugin/migrate/source/CSV.php

@@ -3,6 +3,7 @@
 namespace Drupal\migrate_source_csv\Plugin\migrate\source;
 
 use Drupal\Component\Plugin\ConfigurableInterface;
+use Drupal\Component\Plugin\Exception\InvalidPluginDefinitionException;
 use Drupal\Component\Utility\NestedArray;
 use Drupal\migrate\Plugin\MigrationInterface;
 use Drupal\migrate\Plugin\migrate\source\SourcePluginBase;
@@ -185,14 +186,17 @@ class CSV extends SourcePluginBase implements ConfigurableInterface {
    *
    * @return string
    *   The file path.
+   *
+   * @throws \Drupal\Component\Plugin\Exception\InvalidPluginDefinitionException
    */
   public function __toString() {
-    return $this->configuration['path'];
+    return $this->getPath();
   }
 
   /**
    * {@inheritdoc}
    *
+   * @throws \Drupal\Component\Plugin\Exception\InvalidPluginDefinitionException
    * @throws \Drupal\migrate\MigrateException
    * @throws \League\Csv\Exception
    */
@@ -263,6 +267,7 @@ class CSV extends SourcePluginBase implements ConfigurableInterface {
    * @return \League\Csv\Reader
    *   The reader.
    *
+   * @throws \Drupal\Component\Plugin\Exception\InvalidPluginDefinitionException
    * @throws \Drupal\migrate\MigrateException
    * @throws \League\Csv\Exception
    */
@@ -280,16 +285,49 @@ class CSV extends SourcePluginBase implements ConfigurableInterface {
    *
    * @return \League\Csv\Reader
    *   The reader.
+   *
+   * @throws \Drupal\Component\Plugin\Exception\InvalidPluginDefinitionException
    */
   protected function createReader() {
-    if (!file_exists($this->configuration['path'])) {
-      throw new \RuntimeException(sprintf('File "%s" was not found.', $this->configuration['path']));
+    $path = $this->getPath();
+    if (!file_exists($path)) {
+      throw new \RuntimeException(sprintf('File "%s" was not found.', $path));
     }
-    $csv = fopen($this->configuration['path'], 'r');
+    $csv = fopen($path, 'r');
     if (!$csv) {
-      throw new \RuntimeException(sprintf('File "%s" could not be opened.', $this->configuration['path']));
+      throw new \RuntimeException(sprintf('File "%s" could not be opened.', $path));
     }
     return Reader::createFromStream($csv);
   }
 
+  /**
+   * Gets the path from configuration.
+   *
+   * @return string
+   *   The path.
+   *
+   * @throws \Drupal\Component\Plugin\Exception\InvalidPluginDefinitionException
+   */
+  protected function getPath() {
+    $path = $this->configuration['path'];
+
+    // Support a callback to return the path.
+    if (is_array($path)) {
+      if (!isset($path['callback'])) {
+        throw new InvalidPluginDefinitionException($this->getPluginId(), 'The path is an array, but the callback function is not defined.');
+      }
+      if (!is_callable($path['callback'])) {
+        throw new InvalidPluginDefinitionException($this->getPluginId(), 'The path callback function is not callable.');
+      }
+
+      $path = call_user_func($path['callback']);
+
+      if (!is_string($path)) {
+        throw new InvalidPluginDefinitionException($this->getPluginId(), 'The path callback function did not return a string.');
+      }
+    }
+
+    return $path;
+  }
+
 }

[Lucas Hedding]

can we do a check if string and return that first? that would operate as a guard condition very early.

[Lucas Hedding]

-      if (!isset($path['callback'])) {
+      if (!array_key_exists('callback', $path)) {