[dart] Preserve inner generic type for Map<String, List<T>> deserialization

[EddieRydell]

Fixes #19997

When generating Dart code for Map<String, List<T>> properties (e.g., Map<String, List<int>>), the fromJson deserialization was losing the inner generic type:

Previous code:

calendar: mapCastOfType<String, List>(json, r'calendar'),
// Results in Map<String, List<dynamic>> - inner type lost

Fixed code:

calendar: (json[r'calendar'] as Map<String, dynamic>).map(
  (k, v) => MapEntry(k, v == null ? const <T>[] : (v as List).cast<T>())),
  // Inner type T preserved

Changes

• Updated native_class.mustache template to properly cast inner List types
• Added map_of_array_integer test property to AdditionalPropertiesClass in the Dart petstore spec

---

Summary by cubic

Preserves the inner generic type when deserializing Map<String, List> in generated Dart models, preventing List in values. Fixes #19997 and ensures correct typing (e.g., Map<String, List>).

• Bug Fixes
  • Updated dart2 native_class.mustache to map and cast list values (v as List).cast(), with null-safe defaults (empty list or null when nullable).
  • Added map_of_array_integer to the petstore spec to cover Map<String, List> and updated the generated model and docs.

^{Written for commit 923af7d. Summary will update on new commits.}

[cubic-dev-ai]

2 issues found across 4 files

Prompt for AI agents (all issues)

Check if these issues are valid — if so, understand the root cause of each and fix them.


<file name="modules/openapi-generator/src/main/resources/dart2/serialization/native/native_class.mustache">

<violation number="1" location="modules/openapi-generator/src/main/resources/dart2/serialization/native/native_class.mustache:166">
P2: Map<String, List<Enum>> deserialization now casts lists to the enum type without converting JSON strings, causing a runtime TypeError for enum values.</violation>
</file>

<file name="samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/additional_properties_class.dart">

<violation number="1" location="samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/additional_properties_class.dart:38">
P2: hashCode uses map identity while == uses deep equality for mapOfArrayInteger, breaking equality contract</violation>
</file>

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[EddieRydell]

Hey @wing328, just checking in on this — CI is all green and I think I addressed the review comments. Is there anything else needed on my end?

I've got a couple more Dart deserialization fixes I'm planning to submit once this one lands, so would love to get it through when you get a chance. Thanks!

[wing328]

thanks for the PR

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