reverted:
--- b/core/modules/migrate/src/Plugin/MigrateSourcePluginManager.php
+++ a/core/modules/migrate/src/Plugin/MigrateSourcePluginManager.php
@@ -7,7 +7,6 @@
 use Drupal\migrate\Plugin\Discovery\AnnotatedClassDiscoveryAutomatedProviders;
 use Drupal\Core\Plugin\Discovery\ContainerDerivativeDiscoveryDecorator;
 use Drupal\migrate\Plugin\Discovery\ProviderFilterDecorator;
-use Drupal\migrate\Plugin\Exception\BadPluginDefinitionException;
 
 /**
  * Plugin manager for migrate source plugins.
@@ -71,15 +70,4 @@
     });
   }
 
-  /**
-   * {@inheritdoc}
-   */
-  public function processDefinition(&$definition, $plugin_id) {
-    parent::processDefinition($definition, $plugin_id);
-
-    if (empty($definition['source_module'])) {
-      throw new BadPluginDefinitionException($plugin_id, 'source_module');
-    }
-  }
-
 }
diff -u b/core/modules/migrate/tests/src/Kernel/Plugin/MigrationProvidersExistTest.php b/core/modules/migrate/tests/src/Kernel/Plugin/MigrationProvidersExistTest.php
--- b/core/modules/migrate/tests/src/Kernel/Plugin/MigrationProvidersExistTest.php
+++ b/core/modules/migrate/tests/src/Kernel/Plugin/MigrationProvidersExistTest.php
@@ -22,7 +22,7 @@
   public function testSourceProvider() {
     $this->enableModules(['migration_provider_test']);
     $this->setExpectedException(BadPluginDefinitionException::class, 'The no_source_module plugin should define the source_module property.');
-    $this->container->get('plugin.manager.migrate.source')->getDefinitions();
+    $this->container->get('plugin.manager.migration')->getDefinition('migration_provider_no_annotation');
   }
 
   /**