[BUG][DART-DIO] Invalid generics for additionalProperties without type

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator?
• Have you tested with the latest master to confirm the issue still exists?
• Have you searched for related issues/PRs?
• What's the actual output vs expected output?
• [Optional] Sponsorship to speed up the bug fix or feature request (example)

Description

Model property with additionalProperties: {...} but without type: object producing BuildMap with a single type parameter rather than two, so the code does not compile:

Actual:

  BuiltMap<String>? get mapField;

Expected (with explicit type: object):

  BuiltMap<String, String>? get mapField;

openapi-generator version

7.21.0. I don't know if it's a regression, I just noticed it wasn't working.

OpenAPI declaration file content or url

openapi: 3.1.0

info:
  version: 0.0.0
  title: Dart bug

components:
  schemas:
    InvalidMap:
      properties:
        mapField:
          #type: object
          additionalProperties:
            type: string

Generation Details

java -jar openapi-generator-cli-7.21.0.jar generate -g dart-dio -o out -i api.yaml

Steps to reproduce

See spec and generation details above.

Related issues/PRs

Suggest a fix

The problem appears to be that variable_type.mustache uses {{baseType}} and {{isMap}} (code). baseType appears to be derived from DefaultCodegen.getPrimitiveType, which returns "map", but isMap appears to be derived from IJsonSchemaValidationProperties.setTypeProperties, which goes down the isAnyType before isMapSchema (code). Adjusting the order in setTypeProperties to be consistent with getPrimitiveType probably fixes the problem.

Start with modules/openapi-generator/src/main/resources/dart/libraries/dio/serialization/built_value/variable_type.mustache and IJsonSchemaValidationProperties.setTypeProperties, then compare that logic with DefaultCodegen.getPrimitiveType. Reproduce the issue using the provided api.yaml and dart-dio generation command. Done means the generated map uses two type parameters and compiles for additionalProperties without an explicit object type.