14 files declare their use of MigrateSource

CacheableEmbeddedDataSource.php in core/modules/migrate/tests/modules/migrate_cache_counts_test/src/Plugin/migrate/source/CacheableEmbeddedDataSource.php
ConfigEntity.php in core/modules/migrate/src/Plugin/migrate/source/ConfigEntity.php
ContentEntity.php in core/modules/migrate/src/Plugin/migrate/source/ContentEntity.php
EmbeddedDataSource.php in core/modules/migrate/src/Plugin/migrate/source/EmbeddedDataSource.php
EmptySource.php in core/modules/migrate/src/Plugin/migrate/source/EmptySource.php
HighWaterTest.php in core/modules/migrate/tests/modules/migrate_high_water_test/src/Plugin/migrate/source/HighWaterTest.php
MigrateExternalTranslatedTestSource.php in core/modules/migrate/tests/modules/migrate_external_translated_test/src/Plugin/migrate/source/MigrateExternalTranslatedTestSource.php
MigrateMissingDatabaseSource.php in core/modules/migrate/tests/modules/migrate_missing_database_test/src/Plugin/migrate/source/MigrateMissingDatabaseSource.php
MigrateSourcePluginManager.php in core/modules/migrate/src/Plugin/MigrateSourcePluginManager.php
QueryBatchTest.php in core/modules/migrate/tests/modules/migrate_query_batch_test/src/Plugin/migrate/source/QueryBatchTest.php
SimpleSource.php in core/modules/migrate/tests/modules/migrate_plugin_config_test/src/Plugin/migrate/source/SimpleSource.php
SqlCountCache.php in core/modules/migrate/tests/modules/migrate_sql_count_cache_test/src/Plugin/migrate/source/SqlCountCache.php
TestSqlPrepareQuery.php in core/modules/migrate/tests/modules/migrate_sql_prepare_query_test/src/Plugin/migrate/source/TestSqlPrepareQuery.php
TrackChangesTest.php in core/modules/migrate/tests/modules/migrate_track_changes_test/src/Plugin/migrate/source/TrackChangesTest.php

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