[BUG][dart-dio] syntax error stopping build_runner from completing

dart-dio fails to generate the Twitter v2 API spec. The outputted code has syntax errors that does not allow build_runner to generate the final pieces of code

https://api.twitter.com/2/openapi.json

openapi.json.zip

openapi-generator-cli 5.4.0
  commit : 4a36be7
  built  : 2022-01-31T05:31:36Z
  source : https://github.com/openapitools/openapi-generator
  docs   : https://openapi-generator.tech/

openapi-generator generate -i spec.json -g dart-dio -o dart_dio_client
cd dart_dio_client
dart pub get
dart run build_runner build --delete-conflicting-outputs

[SEVERE] built_value_generator:built_value on test/spaces_api_test.dart:

Bad state: Unexpected diagnostics:
/Users/lukepighetti/development/flutter/flutter/bin/cache/dart-sdk/lib/core/int.dart:167:18 - Operator declarations must be preceded by the keyword 'operator'.
/Users/lukepighetti/development/flutter/flutter/bin/cache/dart-sdk/lib/core/int.dart:167:16 - Methods must have an explicit list of parameters.
/Users/lukepighetti/development/flutter/flutter/bin/cache/dart-sdk/lib/core/int.dart:167:18 - A function body must be provided.

Related to:

• https://github.com/OpenAPITools/openapi-generator/issues/2567
• https://github.com/OpenAPITools/openapi-generator/pull/6913

Reproduce the generation using the linked openapi.json and the dart-dio command, then run dart run build_runner build --delete-conflicting-outputs in the generated client. Start with the generated code referenced by test/spaces_api_test.dart and the reported int.dart diagnostics; done means the Twitter v2 client builds without the syntax errors.