Use 'source_module' and 'destination_module' annotation to indicate module responsible for migration

The migrate_drupal_ui module displays a confirmation form indicating what source and destination modules have (or do not have) migration paths defined. Because the source and destination modules for an upgrade path are not always the same, and there was no means to automatically determine in every case what modules a migration applied for, the UI module contained a hard-coded list of migrations and their related source and destination modules. This meant there was no way for the UI to know about contributed module migration paths, and also that core changes to the migration list required editing this list.

The UI now looks for source and destination module information on the source and destination plugins in order to build the confirmation form. A module implementing Drupal-to-Drupal migrations must add source and destination module information where appropriate for those migrations to be properly reflected on the confirmation form.

All source and destination plugins must define a source_module or destination_module, respectively, in their plugin definition/annotation, or an exception will be thrown by the plugin discovery service. If the source module or destination module is defined in the migration yml file as well, that value will take precedence.

Source plugin

Add a source_module to your source plugin annotation:

Previously:

  * @MigrateSource(
  *   id = "d6_box"
  * )

Now:

  * @MigrateSource(
  *   id = "d6_box",
  *   source_module = "block",
  * )

If the source module is ambiguous, or may vary depending on how the migration is configured (most frequently in Drupal-to-Drupal migrations, this would be the 'variable' source plugin), you can set an arbitrary value in the plugin definition, then override it in your source plugin configuration. (Note that source_module must be added to any migration using the 'variable' source plugin.)

Previously:

source:
  plugin: variable

Now:

source:
  plugin: variable
  source_module: action

Destination plugin

If your migration uses a custom destination plugin (defined in your module), add destination_module to your destination plugin annotation.

 * @MigrateDestination(
 *   id = "entity:commerce_order",
 *   destination_module = "commerce_order"
 * )

The 'config' destination plugin automatically determines the destination module from the destination config_name (e.g., from action.settings it deduces that 'action' is the destination module). Migrations not using the config destination plugin should add destination_module to the destination configuration.

Previously:

destination:
  plugin: entity:action

Now:

destination:
  plugin: entity:action
  destination_module: action