[BUG][JAVA][SPRING] Wrong annotation used for array of referenced object in Multipart request

Created by: MetroMarv

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

When we specify the request body as multipart/form-data and have one property of type array.

The generated annotation for the statusArray property is "@RequestParam". Which leads to following error in Spring when the endpoint is used:

org.springframework.web.method.annotation.MethodArgumentConversionNotSupportedException:
Failed to convert value of type 'java.lang.String' to required type 'List.of<MultipartMixedStatus>';

Expected would be the annotation "@RequestPart" which fixes the Spring error.

openapi-generator version

6.2.1

But the problem was probably introduced in #11449 with version 6.0.0 (thanks to @borsch to figure this out)

OpenAPI declaration file content or url

[...]
requestBody:
  content:
    multipart/form-data:
      schema:
        type: object
        properties:
          file:
            description: "a file"
            type: string
            format: binary
          statusArray:
            type: array
            items:
              $ref: '#/components/schemas/MultipartMixedStatus'
[...]

Generation Details

We used the Maven plugin with following config

        <configuration>
          <templateDirectory>openapi-generator-customization</templateDirectory>
          <generatorName>spring</generatorName>
          <modelNameSuffix>Dto</modelNameSuffix>
          <configOptions>
            <useSpringBoot3>true</useSpringBoot3>
            <documentationProvider>springdoc</documentationProvider>
            <useTags>true</useTags>
            <useBeanValidation>true</useBeanValidation>
            <performBeanValidation>true</performBeanValidation>
            <useSpringController>true</useSpringController>
            <oas3>true</oas3>
            <apiPackage>com.example.api</apiPackage>
            <modelPackage>com.example.model</modelPackage>
            <invokerPackage>com.example.invoker</invokerPackage>
            <interfaceOnly>true</interfaceOnly>
            <skipOverwrite>false</skipOverwrite>
          </configOptions>
        </configuration>

Steps to reproduce

See test in PR #14450.

Related issues/PRs

• #14295 (closed) fixed the problem for not wrapped objects
• #11449 might have introduced the problem

Suggest a fix

Fixed by: #14450