[BUG] Enum not generated properly, if there is a class + property with the same name

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• 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

openapi-generator version

6.2.1, don't know whether it is a regression. I am a new user.

OpenAPI declaration file content or url

Gist: https://gist.github.com/felixscheinost/dfdd51e75f665e676d79b70f9acea7e4

Generation Details

yarn init
yarn add -D @openapitools/openapi-generator-cli
yarn run openapi-generator-cli generate -i swagger-bug.json -g kotlin -o /tmp/test

Steps to reproduce

• Generate using above steps.

• ApiErrorGroup.kt is NOT a enum, as it should be. is an empty data class instead.

Changes to schema which change the bug:

• Renaming ApiError#group => ApiError#group2, in this case a empty data class ApiErrorGroup2 is created, which also won't compile. But the enum ApiErrorGroup is generated correctly.

• Removing the unnecessary oneOf. Yeah, the oneOf is unnecessary here but the schema is generated by another party which we don't have control over. It should also be valid so valid code should be generated regardless.

Related issues/PRs

Suggest a fix

Start by reproducing the issue with the provided gist and the openapi-generator-cli Kotlin command. Inspect the generated ApiErrorGroup.kt and the related ApiError and enum output; done means the class/property name collision produces a valid enum and compiling generated Kotlin code, including with the unnecessary oneOf present.