[BUG] Generator Spring creates duplicate "inner" models for array reference types

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

In specific circumstances, starting with openapi-generator-maven version 7.8.0, on specific systems, generates undesired extra models for referenced array types. Instead of using the defined referenced model. I've tried to create an MVP that should generate the same results for everyone.

openapi-generator version

• 7.8.0
• 7.9.0
• 7.10.0
• 7.11.0
• 7.12.0
• 7.13.0

OpenAPI declaration file content or url

api.yaml

openapi: 3.1.1
info:
  title: Duplicate model example
  version: 0.0.0-SNAPSHOT
servers:
  - url: /api
paths:
  /test:
    put:
      responses:
        '200':
          description: example
          content:
            'application/json;charset=UTF-8':
              schema:
                $ref: '#/components/schemas/ExampleType'
components:
  schemas:
    ExampleType:
      type: object
      required:
        - arrayType
      properties:
        arrayType:
          type: array
          items:
            $ref: '#/components/schemas/SubType'
    SubType:
      type: object
      properties:
        namedField:
          type: string

Generation Details

> docker run --rm --volume "${PWD}:/java-build" --workdir "/java-build" maven:3.9-eclipse-temurin-21-alpine mvn clean openapi-generator:generate enforcer:enforce
(...)
[INFO] writing file /java-build/target/generated-sources/openapi/src/gen/java/com/example/openapi/inner/api/model/RestExampleType.java
[INFO] writing file /java-build/target/generated-sources/openapi/src/gen/java/com/example/openapi/inner/api/model/RestExampleTypeArrayTypeInner.java
[INFO] writing file /java-build/target/generated-sources/openapi/src/gen/java/com/example/openapi/inner/api/model/RestSubType.java
(...)
[ERROR] Some files should not exist:
[ERROR] /java-build/target/generated-sources/openapi/src/gen/java/com/example/openapi/inner/api/model/RestExampleTypeArrayTypeInner.java
(...)

pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>

  <groupId>com.example.openapi.inner</groupId>
  <artifactId>test</artifactId>
  <version>0.0.1-SNAPSHOT</version>
  <packaging>jar</packaging>
  <name>test</name>

  <properties>
    <java.version>21</java.version>
    <main.package>com.example.openapi.inner</main.package>

    <openapi-generator.version>7.13.0</openapi-generator.version>
    <jakarta-validation.version>3.1.0</jakarta-validation.version>
    <swagger.version>2.2.25</swagger.version>
    <openapi-jackson.version>0.2.6</openapi-jackson.version>
  </properties>

  <dependencies>
    <dependency>
      <groupId>jakarta.validation</groupId>
      <artifactId>jakarta.validation-api</artifactId>
      <version>${jakarta-validation.version}</version>
    </dependency>
    <dependency>
      <groupId>io.swagger.core.v3</groupId>
      <artifactId>swagger-annotations</artifactId>
      <version>${swagger.version}</version>
    </dependency>
    <dependency>
      <groupId>org.openapitools</groupId>
      <artifactId>jackson-databind-nullable</artifactId>
      <version>${openapi-jackson.version}</version>
    </dependency>
    <dependency>
      <groupId>io.swagger.core.v3</groupId>
      <artifactId>swagger-models</artifactId>
      <version>${swagger.version}</version>
    </dependency>
  </dependencies>

  <build>
    <plugins>
      <plugin>
        <groupId>org.openapitools</groupId>
        <artifactId>openapi-generator-maven-plugin</artifactId>
        <version>${openapi-generator.version}</version>
        <configuration>
          <inputSpec>${project.baseUri}/api.yaml</inputSpec>
          <generatorName>spring</generatorName>
          <output>target/generated-sources/openapi</output>
          <groupId>${main.package}</groupId>
          <packageName>${main.package}</packageName>
          <apiPackage>${main.package}.api</apiPackage>
          <modelPackage>${main.package}.api.model</modelPackage>
          <artifactId>backend</artifactId>
          <modelNamePrefix>Rest</modelNamePrefix>
          <generateApiTests>false</generateApiTests>
          <generateModelTests>false</generateModelTests>
          <generateSupportingFiles>false</generateSupportingFiles>
          <configOptions>
            <skipDefaultInterface>true</skipDefaultInterface>
            <sourceFolder>src/gen/java</sourceFolder>
            <useOptional>true</useOptional>
            <openApiNullable>false</openApiNullable>
            <interfaceOnly>true</interfaceOnly>
            <unhandledException>true</unhandledException>
            <useAbstractionForFiles>true</useAbstractionForFiles>
            <useSpringBoot3>true</useSpringBoot3>
            <useTags>true</useTags>
          </configOptions>
        </configuration>
      </plugin>

      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-enforcer-plugin</artifactId>
        <version>3.5.0</version>
        <configuration>
          <rules>
            <requireFilesDontExist>
              <files>
                <file>${project.build.directory}/generated-sources/openapi/src/gen/java/com/example/openapi/inner/api/model/RestExampleTypeArrayTypeInner.java</file>
              </files>
            </requireFilesDontExist>
          </rules>
          <fail>true</fail>
        </configuration>
      </plugin>
    </plugins>
  </build>
</project>

Steps to reproduce

add above information to a pom.xml and api.yaml in a folder and run provided command line to (hopefully) get the resulting console output and 3 generated models. The one suffixed with "inner" should not exist.

Running with docker should always result in the duplicate model being generated, running normally under windows with mvn clean openapi-generator:generate@openapi-generate should generate only 2 models instead of 3.

As of testing on 28-04-2025, this also structurally fails on windows on version 7.8 and up. (I'm not sure what changed in my local environment to cause this)

Related issues/PRs

not aware of related issues

Suggest a fix

Reproduce the issue with the provided api.yaml and pom.xml by running the Docker Maven command, then compare the generated models with the Windows result. Trace the Spring generator's handling of the array reference in ExampleType; done means the referenced SubType is used and RestExampleTypeArrayTypeInner.java is not generated.