[JAVA] "allOf" with an enum in schema does not generate in Java properly

Description

I am working with a third party to convert their schema to Java. Unfortunately, the way they have done their enums has rendered them nearly unusable in Java. Please note that I cannot alter this schema. While I have played around with it for debugging purposes, I ultimately cannot change it for production.

Swagger-codegen version

3.034

Swagger declaration file content or url

The third party has provided both a json and yml version of their schema with equal results on my part.

  schemas:
    Employee:
      type: object
      properties:
        EmployeeGender:
          $ref: '#/components/schemas/Gender'
    Gender:
      allOf:
        - type: string
        - enum:
            - Female
            - Male

YAML

And here is the same thing in JSON:

"components": {
        "schemas": {
          "Employee": {
                "type": "object",
                "properties": {
                    "EmployeeGender": {"$ref": "#/components/schemas/Gender"}
                }
          },
          "Gender": {
                "allOf": [
                    {"type": "string"},
                    {
                        "enum": [
                            "Female",
                            "Male"
                        ]
                    }
                ]
            }
        }

JSON

It then presents me with Java that has no usable enums.

public class EmployeeGender {

  @Override
  public boolean equals(java.lang.Object o) {
    if (this == o) {
      return true;
    }
    if (o == null || getClass() != o.getClass()) {
      return false;
    }
    return true;
  }

  @Override
  public int hashCode() {
    return Objects.hash();
  }


  @Override
  public String toString() {
    StringBuilder sb = new StringBuilder();
    sb.append("class EmployeeGender {\n");
    
    sb.append("}");
    return sb.toString();
  }

  /**
   * Convert the given object to string with each line indented by 4 spaces
   * (except the first line).
   */
  private String toIndentedString(java.lang.Object o) {
    if (o == null) {
      return "null";
    }
    return o.toString().replace("\n", "\n    ");
  }

}

Obviously I would rather have something like:

public enum EmployeeGender {
  Female("Female"),
  Male("Male");

Command line used for generation

I have not used the command line, as this is generated through maven using Java 17. I will paste the relevant properties in my pom.xml:

        <dependency>
            <groupId>io.swagger.core.v3</groupId>
            <artifactId>swagger-annotations</artifactId>
            <version>2.2.1</version>
        </dependency>
        <dependency>
            <groupId>com.fasterxml.jackson.dataformat</groupId>
            <artifactId>jackson-dataformat-xml</artifactId>
            <version>2.13.3</version>
        </dependency>

And the plugin:

            <plugin>
                <groupId>io.swagger.codegen.v3</groupId>
                <artifactId>swagger-codegen-maven-plugin</artifactId>
                <version>3.0.34</version>
                <executions>
                    <execution>
                        <id>aproject</id>
                        <goals>
                            <goal>generate</goal>
                        </goals>
                    </execution>
                </executions>
                <configuration>
                    <inputSpec>${project.basedir}/resources/schema.yml</inputSpec>
                    <language>java</language>
                    <library>resttemplate</library>
                    <generateApis>false</generateApis>
                    <apiPackage>this.is.a.package</apiPackage>
                    <modelPackage>this.is.a.package</modelPackage>
                    <invokerPackage>this.is.a.package</invokerPackage>
                    <generateApiTests>false</generateApiTests>
                    <generateApiDocumentation>false</generateApiDocumentation>
                    <generateModelTests>false</generateModelTests>
                    <generateModelDocumentation>false</generateModelDocumentation>
                    <generateSupportingFiles>true</generateSupportingFiles>
                    <configOptions>
                        <interfaceOnly>true</interfaceOnly>
                        <dateLibrary>legacy</dateLibrary>
                    </configOptions>
                </configuration>
            </plugin>

I then run a mvn clean swagger-codegen:generate or maven clean compile or whatever I need.

Steps to reproduce

1. Set up schema as shown and pom.xml as shown, either using the json or yml file for generation. (Both have the same results for me)
2. Run mvn clean swagger-codegen:generate or maven clean compile or any other maven command that would generate the code.
3. Check the relevant generated Java files. I would expect the enums to generate enum Java files instead of whatever mess they end up generating.

Related issues/PRs

Issue 1746
Issue 2450
Issue 10446

Suggest a fix/enhancement

From my testing and messing with the schemas, removing the "allOf" from the enum in the schema will produce the Java class I am looking for. However, I cannot alter the schema for production. I need a fix within the code generation itself.

Reproduce the generation with the supplied schema.yml or JSON and pom.xml using the swagger-codegen Maven plugin. Inspect the generated Java for the allOf enum case and compare it with the expected Female and Male enum values; done means the schema generates a usable Java enum rather than an empty model class.