[dart-dio] fix the issue of multi layer issues with dart-dio code generation

FS
7d ago
+2662-363

This fixes the issues with multi layer class using oneOf in dart-dio
fixes #15467

The PR includes test for dart-dio, which are using the example from the ticket

@jaumard (2018/09) @josh-burton (2019/12) @amondnet (2019/12) @sbu-WBT (2020/12) @kuhnroyal (2020/12) @agilob (2020/12) @ahmednfwela (2021/08)

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Summary by cubic

Fixes multi-level oneOf/anyOf discriminator dispatch and unifies path/query/form encoding in dart-dio, preventing wrong model selection and unsafe/incorrect serialization (enums, nulls, collections, and reserved path characters). Old behavior: parent-first discriminator checks and ad-hoc encoders that emitted Dart enum identifiers, kept nulls, mishandled containers, and left path values unencoded. New behavior: inheritance-aware discriminator mapping and dedicated encoders that produce wire values, drop nulls safely, handle collections/iterables, and URI-encode path segments.

  • Discriminators: honor only schema-declared mappings for local discriminators; for inherited discriminators include true allOf descendants plus the schema's oneOf/anyOf; order checks by inheritance depth (fixes #15467, #23717).
  • Path params: use encodePathParameter(...) throughout; URI-encodes reserved chars and emits enum wire values (via serializers) instead of Dart identifiers; built_value uses serializers for enum wire names and supports lists/maps/iterables with ListFormat.
  • Query/form params: unify to encodeParameter(...); drop optional null form parameters without sending empty strings; keep required nullable form entries; handle nullable query collection items; ship api_util.dart for both built_value and json_serializable.
  • Serializers: generate ListBuilder<T?>/SetBuilder<T?> when item types are nullable to align with FullType.nullable(...).
  • Tests/samples: add coverage for local vs inherited discriminators, enum wire-value encoding in path params and collections, iterable path serialization, required-nullable form signatures, and nullable collection item serialization; regenerate dart-dio samples accordingly.