Migration Mapping Validator

Provides a Drush utility that validates migrate source mappings before import. It checks that fields referenced in process mappings exist on the migration source plugin.

Validate all migrations:

drush migrate:mapping-validate

Validate specific migrations:

drush migrate:mapping-validate my_migration another_migration

• Extracts referenced source field names from process mappings.
• Compares them against fields exposed by the source plugin (fields() + IDs).
• Reports missing fields as errors and exits with a non-zero status.

• Some source plugins do not implement fields(). Those migrations are reported with a warning and skipped.
• Complex or custom process plugins that reference source properties indirectly may require manual review.
• Pipeline references (values prefixed with @) and constants/* mappings are ignored during validation.