[BUG] [kotlin-spring] Multipart with JSON array broken

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• 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?
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Description

The following schema for a multi-part request consists of an array of strings and a binary file:

paths:
  /jobs/new:
    post:
      summary: Post a new job request
      requestBody:
        content:
          'multipart/form-data':
            schema:
              type: object
              properties:
                commandLine:
                  type: array
                  items:
                    type: string
                workspaceTree:
                  type: string
                  format: binary

The expectation is that each of the parts are processed according to their provided content-type. For the array part however, if a request is prepared using 'applicatin/json' as content-type, the parsed array is treatead as a comma-separated string and the result is wrong.

The generated interface is:

    @RequestMapping(
            method = [RequestMethod.POST],
            value = ["/jobs/new"],
            produces = ["application/json"],
            consumes = ["multipart/form-data"]
    )
    fun jobsNewPost( @Valid @RequestParam(value = "commandLine", required = true) commandLine: kotlin.collections.List<kotlin.String> , @Valid @RequestPart("workspaceTree", required = false) workspaceTree: org.springframework.web.multipart.MultipartFile?): ResponseEntity<java.util.UUID> {

where the commandLine parameters is annotated with RequestParam instead of RequestPart. Changing this annotation manually makes it work.

openapi-generator version

7.13

OpenAPI declaration file content or url

Generation Details

Steps to reproduce

Related issues/PRs

Suggest a fix

I suspect that the fix should make sure that all parts are annotated with RequestPart, but I don't know if there are exceptions to this.

Start by generating the Kotlin Spring interface from the supplied multipart/form-data schema and inspect how the commandLine array is mapped. The fix is complete when the array part is generated with RequestPart rather than RequestParam and is processed as JSON instead of a comma-separated string.