[BUG] Generated code references non-existent classes on "duplicate" property definitions

[bvschaik]

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

Given the following openapi spec: https://github.com/bvschaik/openapi-nonexistent-class-reproducer/blob/main/spec.json

• One definition of catName as string in CatFields, with title "Given name"
• One Cat with a name property that references CatFields/catName
• One definition of dogName as string in DogFields, also with title "Given name"
• One Dog with a nickname property that references DogFields/dogName

The issue: starting from the OpenAPI generator 7.23.0, this generates a Java Dog class with a property nickname of type DogName. The DogName class is not generated:

public class Dog  {
  @JsonbProperty("nickname")
  protected DogName nickname = null;
  ...
}

In 7.22.0 and lower, the Dog class just has a nickname property of String:

public class Dog  {
  @JsonbProperty("nickname")
  protected String nickname;
  ...
}

Observations:

• If I change the title of either of the field definitions, the issue is not there.
• If I change the type of one of the fields to for example integer, the issue is not there.

Conclusion:

If there are two field definitions with the same type and the same title, the OpenAPI generator will generate code using non-existent classes for one of them.

openapi-generator version

Tested and breaks in: 7.23.0, 7.25.0, latest master

This is a regression: it works fine in 7.22.0

OpenAPI declaration file content or url

https://github.com/bvschaik/openapi-nonexistent-class-reproducer/blob/main/spec.json

Generation Details

Use any typed language (tested with Java, Kotlin):

java -jar openapi-generator.jar generate -g java -i https://raw.githubusercontent.com/bvschaik/openapi-nonexistent-class-reproducer/refs/heads/main/spec.json

Steps to reproduce

1. Generate spec using command above
2. Inspect the Cat and Dog classes - Dog has a property of type DogName, which doesn't exist
3. Compile the code - fails

Related issues/PRs

Might be related to: #24004

Suggest a fix