The "link" plugin does not exist. (core/lib/Drupal/Component/Plugin/Discovery/DiscoveryTrait.php:52)

Got it in the context of drush mi --all too:

Processed 1 item (0 created, 0 updated, 0 failed, 0 ignored) - done with 'upgrade_d6_field_group_entity_view_display'
The "link" plugin does not exist. (/core/lib/Drupal/Component/Plugin/Discovery/DiscoveryTrait.php:52)
Processed 11 items (10 created, 0 updated, 1 failed, 0 ignored) - done with 'upgrade_d6_field_instance_widget_settings'

I do have a source_ids_hash using drush mmsg upgrade_d6_field_instance_widget_settings, but don't know how to go further in order to provide more information to this bug report.

Referencing #2558931: link_default plugin does not exist (d6)

maybe related #2831531: Improved the exception message in d6/FieldTypeDefaults

edited

Since its about Drupal 8.2.2, referencing #2683435: CCK does not exist in Drupal 7, rename Migrate's cckfield plugins to field plugins (currently open), and #2726803: Field formatters with names different than their field type can not be migrated which is also about field formatters, but specifically for D7.

edited

Tracing WidgetPluginManager.php -> createInstance($plugin_id...)

===== createInstance : datetime_timestamp
===== createInstance : datetime_default
===== createInstance : link

And var_dump($definitions) + stacktrace inside DiscoveryTrait.php:

array(23) {
  'datetime_datelist' =>
  array(6) {
    'field_types' =>
    array(1) {
      [0] =>
      string(8) "datetime"
    }
    'multiple_values' =>
    bool(false)
    'id' =>
    string(17) "datetime_datelist"
    'label' =>
    class Drupal\Core\StringTranslation\TranslatableMarkup#1967 (5) {
      protected $string =>
      string(11) "Select list"
      protected $translatedMarkup =>
      NULL
      protected $options =>
      array(0) {
      }
      protected $stringTranslation =>
      NULL
      protected $arguments =>
      array(0) {
      }
    }
    'class' =>
    string(63) "Drupal\\datetime\\Plugin\\Field\\FieldWidget\\DateTimeDatelistWidget"
    'provider' =>
    string(8) "datetime"
  }
  'datetime_default' =>
  array(6) {
    'field_types' =>
    array(1) {
      [0] =>
      string(8) "datetime"
    }
    'multiple_values' =>
    bool(false)
    'id' =>
    string(16) "datetime_default"
    'label' =>
    class Drupal\Core\StringTranslation\TranslatableMarkup#1968 (5) {
      protected $string =>
      string(13) "Date and time"
      protected $translatedMarkup =>
      NULL
      protected $options =>
      array(0) {
      }
      protected $stringTranslation =>
      NULL
      protected $arguments =>
      array(0) {
      }
    }
    'class' =>
    string(62) "Drupal\\datetime\\Plugin\\Field\\FieldWidget\\DateTimeDefaultWidget"
    'provider' =>
    string(8) "datetime"
  }
  'file_generic' =>
  array(6) {
    'field_types' =>
    array(1) {
      [0] =>
      string(4) "file"
    }
    'multiple_values' =>
    bool(false)
    'id' =>
    string(12) "file_generic"
    'label' =>
    class Drupal\Core\StringTranslation\TranslatableMarkup#1969 (5) {
      protected $string =>
      string(4) "File"
      protected $translatedMarkup =>
      NULL
      protected $options =>
      array(0) {
      }
      protected $stringTranslation =>
      NULL
      protected $arguments =>
      array(0) {
      }
    }
    'class' =>
    string(47) "Drupal\\file\\Plugin\\Field\\FieldWidget\\FileWidget"
    'provider' =>
    string(4) "file"
  }
  'image_image' =>
  array(6) {
    'field_types' =>
    array(1) {
      [0] =>
      string(5) "image"
    }
    'multiple_values' =>
    bool(false)
    'id' =>
    string(11) "image_image"
    'label' =>
    class Drupal\Core\StringTranslation\TranslatableMarkup#1970 (5) {
      protected $string =>
      string(5) "Image"
      protected $translatedMarkup =>
      NULL
      protected $options =>
      array(0) {
      }
      protected $stringTranslation =>
      NULL
      protected $arguments =>
      array(0) {
      }
    }
    'class' =>
    string(49) "Drupal\\image\\Plugin\\Field\\FieldWidget\\ImageWidget"
    'provider' =>
    string(5) "image"
  }
  'link_default' =>
  array(6) {
    'field_types' =>
    array(1) {
      [0] =>
      string(4) "link"
    }
    'multiple_values' =>
    bool(false)
    'id' =>
    string(12) "link_default"
    'label' =>
    class Drupal\Core\StringTranslation\TranslatableMarkup#1971 (5) {
      protected $string =>
      string(4) "Link"
      protected $translatedMarkup =>
      NULL
      protected $options =>
      array(0) {
      }
      protected $stringTranslation =>
      NULL
      protected $arguments =>
      array(0) {
      }
    }
    'class' =>
    string(47) "Drupal\\link\\Plugin\\Field\\FieldWidget\\LinkWidget"
    'provider' =>
    string(4) "link"
  }
  'metatag_firehose' =>
  array(6) {
    'field_types' =>
    array(1) {
      [0] =>
      string(7) "metatag"
    }
    'multiple_values' =>
    bool(false)
    'id' =>
    string(16) "metatag_firehose"
    'label' =>
    class Drupal\Core\StringTranslation\TranslatableMarkup#1972 (5) {
      protected $string =>
      string(23) "Advanced meta tags form"
      protected $translatedMarkup =>
      NULL
      protected $options =>
      array(0) {
      }
      protected $stringTranslation =>
      NULL
      protected $arguments =>
      array(0) {
      }
    }
    'class' =>
    string(55) "Drupal\\metatag\\Plugin\\Field\\FieldWidget\\MetatagFirehose"
    'provider' =>
    string(7) "metatag"
  }
  'path' =>
  array(6) {
    'field_types' =>
    array(1) {
      [0] =>
      string(4) "path"
    }
    'multiple_values' =>
    bool(false)
    'id' =>
    string(4) "path"
    'label' =>
    class Drupal\Core\StringTranslation\TranslatableMarkup#1973 (5) {
      protected $string =>
      string(9) "URL alias"
      protected $translatedMarkup =>
      NULL
      protected $options =>
      array(0) {
      }
      protected $stringTranslation =>
      NULL
      protected $arguments =>
      array(0) {
      }
    }
    'class' =>
    string(30) "Drupal\\pathauto\\PathautoWidget"
    'provider' =>
    string(4) "path"
  }
  'redirect_source' =>
  array(7) {
    'field_types' =>
    array(1) {
      [0] =>
      string(4) "link"
    }
    'multiple_values' =>
    bool(false)
    'id' =>
    string(15) "redirect_source"
    'label' =>
    class Drupal\Core\StringTranslation\TranslatableMarkup#1974 (5) {
      protected $string =>
      string(15) "Redirect source"
      protected $translatedMarkup =>
      NULL
      protected $options =>
      array(0) {
      }
      protected $stringTranslation =>
      NULL
      protected $arguments =>
      array(0) {
      }
    }
    'settings' =>
    array(2) {
      'placeholder_url' =>
      string(0) ""
      'placeholder_title' =>
      string(0) ""
    }
    'class' =>
    string(61) "Drupal\\redirect\\Plugin\\Field\\FieldWidget\\RedirectSourceWidget"
    'provider' =>
    string(8) "redirect"
  }
  'text_textarea' =>
  array(6) {
    'field_types' =>
    array(1) {
      [0] =>
      string(9) "text_long"
    }
    'multiple_values' =>
    bool(false)
    'id' =>
    string(13) "text_textarea"
    'label' =>
    class Drupal\Core\StringTranslation\TranslatableMarkup#1975 (5) {
      protected $string =>
      string(25) "Text area (multiple rows)"
      protected $translatedMarkup =>
      NULL
      protected $options =>
      array(0) {
      }
      protected $stringTranslation =>
      NULL
      protected $arguments =>
      array(0) {
      }
    }
    'class' =>
    string(51) "Drupal\\text\\Plugin\\Field\\FieldWidget\\TextareaWidget"
    'provider' =>
    string(4) "text"
  }
  'text_textfield' =>
  array(6) {
    'field_types' =>
    array(1) {
      [0] =>
      string(4) "text"
    }
    'multiple_values' =>
    bool(false)
    'id' =>
    string(14) "text_textfield"
    'label' =>
    class Drupal\Core\StringTranslation\TranslatableMarkup#1976 (5) {
      protected $string =>
      string(10) "Text field"
      protected $translatedMarkup =>
      NULL
      protected $options =>
      array(0) {
      }
      protected $stringTranslation =>
      NULL
      protected $arguments =>
      array(0) {
      }
    }
    'class' =>
    string(52) "Drupal\\text\\Plugin\\Field\\FieldWidget\\TextfieldWidget"
    'provider' =>
    string(4) "text"
  }
  'text_textarea_with_summary' =>
  array(6) {
    'field_types' =>
    array(1) {
      [0] =>
      string(17) "text_with_summary"
    }
    'multiple_values' =>
    bool(false)
    'id' =>
    string(26) "text_textarea_with_summary"
    'label' =>
    class Drupal\Core\StringTranslation\TranslatableMarkup#1977 (5) {
      protected $string =>
      string(24) "Text area with a summary"
      protected $translatedMarkup =>
      NULL
      protected $options =>
      array(0) {
      }
      protected $stringTranslation =>
      NULL
      protected $arguments =>
      array(0) {
      }
    }
    'class' =>
    string(62) "Drupal\\text\\Plugin\\Field\\FieldWidget\\TextareaWithSummaryWidget"
    'provider' =>
    string(4) "text"
  }
  'options_select' =>
  array(6) {
    'field_types' =>
    array(4) {
      [0] =>
      string(16) "entity_reference"
      [1] =>
      string(12) "list_integer"
      [2] =>
      string(10) "list_float"
      [3] =>
      string(11) "list_string"
    }
    'multiple_values' =>
    bool(true)
    'id' =>
    string(14) "options_select"
    'label' =>
    class Drupal\Core\StringTranslation\TranslatableMarkup#1978 (5) {
      protected $string =>
      string(11) "Select list"
      protected $translatedMarkup =>
      NULL
      protected $options =>
      array(0) {
      }
      protected $stringTranslation =>
      NULL
      protected $arguments =>
      array(0) {
      }
    }
    'class' =>
    string(62) "Drupal\\Core\\Field\\Plugin\\Field\\FieldWidget\\OptionsSelectWidget"
    'provider' =>
    string(4) "core"
  }
  'language_select' =>
  array(6) {
    'field_types' =>
    array(1) {
      [0] =>
      string(8) "language"
    }
    'multiple_values' =>
    bool(false)
    'id' =>
    string(15) "language_select"
    'label' =>
    class Drupal\Core\StringTranslation\TranslatableMarkup#1979 (5) {
      protected $string =>
      string(15) "Language select"
      protected $translatedMarkup =>
      NULL
      protected $options =>
      array(0) {
      }
      protected $stringTranslation =>
      NULL
      protected $arguments =>
      array(0) {
      }
    }
    'class' =>
    string(63) "Drupal\\Core\\Field\\Plugin\\Field\\FieldWidget\\LanguageSelectWidget"
    'provider' =>
    string(4) "core"
  }
  'string_textfield' =>
  array(6) {
    'field_types' =>
    array(1) {
      [0] =>
      string(6) "string"
    }
    'multiple_values' =>
    bool(false)
    'id' =>
    string(16) "string_textfield"
    'label' =>
    class Drupal\Core\StringTranslation\TranslatableMarkup#1980 (5) {
      protected $string =>
      string(9) "Textfield"
      protected $translatedMarkup =>
      NULL
      protected $options =>
      array(0) {
      }
      protected $stringTranslation =>
      NULL
      protected $arguments =>
      array(0) {
      }
    }
    'class' =>
    string(64) "Drupal\\Core\\Field\\Plugin\\Field\\FieldWidget\\StringTextfieldWidget"
    'provider' =>
    string(4) "core"
  }
  'entity_reference_autocomplete' =>
  array(7) {
    'field_types' =>
    array(1) {
      [0] =>
      string(16) "entity_reference"
    }
    'multiple_values' =>
    bool(false)
    'id' =>
    string(29) "entity_reference_autocomplete"
    'label' =>
    class Drupal\Core\StringTranslation\TranslatableMarkup#1981 (5) {
      protected $string =>
      string(12) "Autocomplete"
      protected $translatedMarkup =>
      NULL
      protected $options =>
      array(0) {
      }
      protected $stringTranslation =>
      NULL
      protected $arguments =>
      array(0) {
      }
    }
    'description' =>
    class Drupal\Core\StringTranslation\TranslatableMarkup#1982 (5) {
      protected $string =>
      string(27) "An autocomplete text field."
      protected $translatedMarkup =>
      NULL
      protected $options =>
      array(0) {
      }
      protected $stringTranslation =>
      NULL
      protected $arguments =>
      array(0) {
      }
    }
    'class' =>
    string(76) "Drupal\\Core\\Field\\Plugin\\Field\\FieldWidget\\EntityReferenceAutocompleteWidget"
    'provider' =>
    string(4) "core"
  }
  'options_buttons' =>
  array(6) {
    'field_types' =>
    array(5) {
      [0] =>
      string(7) "boolean"
      [1] =>
      string(16) "entity_reference"
      [2] =>
      string(12) "list_integer"
      [3] =>
      string(10) "list_float"
      [4] =>
      string(11) "list_string"
    }
    'multiple_values' =>
    bool(true)
    'id' =>
    string(15) "options_buttons"
    'label' =>
    class Drupal\Core\StringTranslation\TranslatableMarkup#1983 (5) {
      protected $string =>
      string(25) "Check boxes/radio buttons"
      protected $translatedMarkup =>
      NULL
      protected $options =>
      array(0) {
      }
      protected $stringTranslation =>
      NULL
      protected $arguments =>
      array(0) {
      }
    }
    'class' =>
    string(63) "Drupal\\Core\\Field\\Plugin\\Field\\FieldWidget\\OptionsButtonsWidget"
    'provider' =>
    string(4) "core"
  }
  'string_textarea' =>
  array(6) {
    'field_types' =>
    array(1) {
      [0] =>
      string(11) "string_long"
    }
    'multiple_values' =>
    bool(false)
    'id' =>
    string(15) "string_textarea"
    'label' =>
    class Drupal\Core\StringTranslation\TranslatableMarkup#1984 (5) {
      protected $string =>
      string(25) "Text area (multiple rows)"
      protected $translatedMarkup =>
      NULL
      protected $options =>
      array(0) {
      }
      protected $stringTranslation =>
      NULL
      protected $arguments =>
      array(0) {
      }
    }
    'class' =>
    string(63) "Drupal\\Core\\Field\\Plugin\\Field\\FieldWidget\\StringTextareaWidget"
    'provider' =>
    string(4) "core"
  }
  'number' =>
  array(6) {
    'field_types' =>
    array(3) {
      [0] =>
      string(7) "integer"
      [1] =>
      string(7) "decimal"
      [2] =>
      string(5) "float"
    }
    'multiple_values' =>
    bool(false)
    'id' =>
    string(6) "number"
    'label' =>
    class Drupal\Core\StringTranslation\TranslatableMarkup#1985 (5) {
      protected $string =>
      string(12) "Number field"
      protected $translatedMarkup =>
      NULL
      protected $options =>
      array(0) {
      }
      protected $stringTranslation =>
      NULL
      protected $arguments =>
      array(0) {
      }
    }
    'class' =>
    string(55) "Drupal\\Core\\Field\\Plugin\\Field\\FieldWidget\\NumberWidget"
    'provider' =>
    string(4) "core"
  }
  'boolean_checkbox' =>
  array(6) {
    'field_types' =>
    array(1) {
      [0] =>
      string(7) "boolean"
    }
    'multiple_values' =>
    bool(true)
    'id' =>
    string(16) "boolean_checkbox"
    'label' =>
    class Drupal\Core\StringTranslation\TranslatableMarkup#1986 (5) {
      protected $string =>
      string(22) "Single on/off checkbox"
      protected $translatedMarkup =>
      NULL
      protected $options =>
      array(0) {
      }
      protected $stringTranslation =>
      NULL
      protected $arguments =>
      array(0) {
      }
    }
    'class' =>
    string(64) "Drupal\\Core\\Field\\Plugin\\Field\\FieldWidget\\BooleanCheckboxWidget"
    'provider' =>
    string(4) "core"
  }
  'uri' =>
  array(6) {
    'field_types' =>
    array(1) {
      [0] =>
      string(3) "uri"
    }
    'multiple_values' =>
    bool(false)
    'id' =>
    string(3) "uri"
    'label' =>
    class Drupal\Core\StringTranslation\TranslatableMarkup#1987 (5) {
      protected $string =>
      string(9) "URI field"
      protected $translatedMarkup =>
      NULL
      protected $options =>
      array(0) {
      }
      protected $stringTranslation =>
      NULL
      protected $arguments =>
      array(0) {
      }
    }
    'class' =>
    string(52) "Drupal\\Core\\Field\\Plugin\\Field\\FieldWidget\\UriWidget"
    'provider' =>
    string(4) "core"
  }
  'email_default' =>
  array(6) {
    'field_types' =>
    array(1) {
      [0] =>
      string(5) "email"
    }
    'multiple_values' =>
    bool(false)
    'id' =>
    string(13) "email_default"
    'label' =>
    class Drupal\Core\StringTranslation\TranslatableMarkup#1988 (5) {
      protected $string =>
      string(5) "Email"
      protected $translatedMarkup =>
      NULL
      protected $options =>
      array(0) {
      }
      protected $stringTranslation =>
      NULL
      protected $arguments =>
      array(0) {
      }
    }
    'class' =>
    string(61) "Drupal\\Core\\Field\\Plugin\\Field\\FieldWidget\\EmailDefaultWidget"
    'provider' =>
    string(4) "core"
  }
  'entity_reference_autocomplete_tags' =>
  array(7) {
    'field_types' =>
    array(1) {
      [0] =>
      string(16) "entity_reference"
    }
    'multiple_values' =>
    bool(true)
    'id' =>
    string(34) "entity_reference_autocomplete_tags"
    'label' =>
    class Drupal\Core\StringTranslation\TranslatableMarkup#1989 (5) {
      protected $string =>
      string(25) "Autocomplete (Tags style)"
      protected $translatedMarkup =>
      NULL
      protected $options =>
      array(0) {
      }
      protected $stringTranslation =>
      NULL
      protected $arguments =>
      array(0) {
      }
    }
    'description' =>
    class Drupal\Core\StringTranslation\TranslatableMarkup#1990 (5) {
      protected $string =>
      string(48) "An autocomplete text field with tagging support."
      protected $translatedMarkup =>
      NULL
      protected $options =>
      array(0) {
      }
      protected $stringTranslation =>
      NULL
      protected $arguments =>
      array(0) {
      }
    }
    'class' =>
    string(80) "Drupal\\Core\\Field\\Plugin\\Field\\FieldWidget\\EntityReferenceAutocompleteTagsWidget"
    'provider' =>
    string(4) "core"
  }
  'datetime_timestamp' =>
  array(6) {
    'field_types' =>
    array(2) {
      [0] =>
      string(9) "timestamp"
      [1] =>
      string(7) "created"
    }
    'multiple_values' =>
    bool(false)
    'id' =>
    string(18) "datetime_timestamp"
    'label' =>
    class Drupal\Core\StringTranslation\TranslatableMarkup#1991 (5) {
      protected $string =>
      string(18) "Datetime Timestamp"
      protected $translatedMarkup =>
      NULL
      protected $options =>
      array(0) {
      }
      protected $stringTranslation =>
      NULL
      protected $arguments =>
      array(0) {
      }
    }
    'class' =>
    string(69) "Drupal\\Core\\Datetime\\Plugin\\Field\\FieldWidget\\TimestampDatetimeWidget"
    'provider' =>
    string(4) "core"
  }
}

Xdebug: user triggered in d8/core/lib/Drupal/Component/Plugin/Discovery/DiscoveryTrait.php on line 52

Call Stack:
    0.0003     234088   1. {main}() /usr/local/bin/drush8:0
    0.0488     829744   2. require('phar:///usr/local/bin/drush8/drush') /usr/local/bin/drush8:10
    0.0502     895520   3. drush_startup() phar:///usr/local/bin/drush8/drush:114
    0.0508     897232   4. drush_run_main() phar:///usr/local/bin/drush8/includes/startup.inc:365
    0.0536    1065888   5. drush_main() phar:///usr/local/bin/drush8/includes/startup.inc:458
    1.4276   12075288   6. Drush\Boot\BaseBoot->bootstrap_and_dispatch() phar:///usr/local/bin/drush8/includes/preflight.inc:66
    8.3539   37514920   7. drush_dispatch() phar:///usr/local/bin/drush8/lib/Drush/Boot/BaseBoot.php:67
    9.1260   40662504   8. call_user_func_array:{phar:///usr/local/bin/drush8/includes/command.inc:199}() phar:///usr/local/bin/drush8/includes/command.inc:199
    9.1260   40663024   9. drush_command() phar:///usr/local/bin/drush8/includes/command.inc:199
    9.1271   40668240  10. _drush_invoke_hooks() phar:///usr/local/bin/drush8/includes/command.inc:231
    9.1444   40966944  11. call_user_func_array:{phar:///usr/local/bin/drush8/includes/command.inc:422}() phar:///usr/local/bin/drush8/includes/command.inc:422
    9.1444   40967384  12. drush_migrate_tools_migrate_import() phar:///usr/local/bin/drush8/includes/command.inc:422
    9.2575   42250232  13. array_walk() d8/modules/migrate/migrate_tools/migrate_tools.drush.inc:246
    9.2575   42250912  14. _drush_migrate_tools_execute_migration() d8/modules/migrate/migrate_tools/migrate_tools.drush.inc:246
    9.2684   42772568  15. drush_op() d8/modules/migrate/migrate_tools/migrate_tools.drush.inc:280
    9.2685   42773080  16. drush_call_user_func_array() phar:///usr/local/bin/drush8/includes/drush.inc:711
    9.2685   42773128  17. call_user_func_array:{phar:///usr/local/bin/drush8/includes/drush.inc:720}() phar:///usr/local/bin/drush8/includes/drush.inc:720
    9.2685   42775640  18. Drupal\migrate\MigrateExecutable->import() phar:///usr/local/bin/drush8/includes/drush.inc:720
   10.0912   56191240  19. Drupal\migrate\Plugin\migrate\destination\ComponentEntityDisplayBase->import() d8/core/modules/migrate/src/MigrateExecutable.php:252
   10.0934   56198408  20. Drupal\Core\Config\Entity\ConfigEntityBase->save() d8/core/modules/migrate/src/Plugin/migrate/destination/ComponentEntityDisplayBase.php:32
   10.0934   56198408  21. Drupal\Core\Entity\Entity->save() d8/core/lib/Drupal/Core/Config/Entity/ConfigEntityBase.php:637
   10.0934   56198408  22. Drupal\Core\Config\Entity\ConfigEntityStorage->save() d8/core/lib/Drupal/Core/Entity/Entity.php:364
   10.0935   56198504  23. Drupal\Core\Entity\EntityStorageBase->save() d8/core/lib/Drupal/Core/Config/Entity/ConfigEntityStorage.php:259
   10.0935   56198552  24. Drupal\Core\Entity\EntityStorageBase->doPreSave() d8/core/lib/Drupal/Core/Entity/EntityStorageBase.php:389
   10.0952   56207488  25. Drupal\Core\Entity\EntityDisplayBase->preSave() d8/core/lib/Drupal/Core/Entity/EntityStorageBase.php:434
   10.0953   56207536  26. Drupal\Core\Config\Entity\ConfigEntityBase->preSave() d8/core/lib/Drupal/Core/Entity/EntityDisplayBase.php:244
   10.0957   56222344  27. Drupal\Core\Plugin\DefaultLazyPluginCollection->getConfiguration() d8/core/lib/Drupal/Core/Config/Entity/ConfigEntityBase.php:320
   10.0957   56224040  28. Drupal\Component\Plugin\LazyPluginCollection->getIterator() d8/core/lib/Drupal/Core/Config/Entity/ConfigEntityBase.php:114
   10.0961   56225680  29. Drupal\Component\Plugin\LazyPluginCollection->get() d8/core/lib/Drupal/Component/Plugin/LazyPluginCollection.php:148
   10.0961   56225680  30. Drupal\Core\Plugin\DefaultLazyPluginCollection->initializePlugin() d8/core/lib/Drupal/Component/Plugin/LazyPluginCollection.php:80
   10.0961   56225680  31. Drupal\Core\Field\WidgetPluginManager->createInstance() d8/core/lib/Drupal/Core/Plugin/DefaultLazyPluginCollection.php:81
   10.0961   56225680  32. Drupal\Core\Plugin\DefaultPluginManager->getDefinition() d8/core/lib/Drupal/Core/Field/WidgetPluginManager.php:118
   10.0961   56225728  33. Drupal\Core\Plugin\DefaultPluginManager->doGetDefinition() d8/core/lib/Drupal/Component/Plugin/Discovery/DiscoveryCachedTrait.php:25
   10.1097   56225776  34. xdebug_print_function_stack() d8/core/lib/Drupal/Component/Plugin/Discovery/DiscoveryTrait.php:52

The "link" plugin does not exist. (d8/core/lib/Drupal/Component/Plugin/Discovery/DiscoveryTrait.php:53)

Sadly no, but note that running migrations from command line is more buggy than from the UI (but that's another open bug I guess)

Which D6 table's dump are you interested in?