How to swagger annotate multipart form data with resteasy?

At the moment resteasy multi-part constructs are not supported out of the box as e.g jersey FormDataParam and the like (in this case specific framework annotations are resolved into the correct requestBody); while there is ongoing effort to add such support, in the meanwhile you would use something like the following to achieve what you need:

@POST
@Path("/")
@Consumes(MediaType.MULTIPART_FORM_DATA)
@Produces(MediaType.APPLICATION_JSON)
@Operation(summary = "Upload a new image and associated metadata", description = "Long form description saying whatever we want",
    requestBody = @RequestBody(
        content = @Content(
            mediaType = "multipart/form-data",
            schema = @Schema(implementation = MultiRequest.class),
            encoding = @Encoding(
                name = "file",
                contentType = "application/pdf, image/png"
            )
        ))
    ,
    responses = {
        @ApiResponse(responseCode = "200", description = "The UUID of the newly uploaded image"),
        @ApiResponse(responseCode = "403", description = "The provided credentials are insufficient to see this resource."),
        @ApiResponse(responseCode = "415", description = "The provided file type is not supported"),
        @ApiResponse(responseCode = "500", description = "We messed up. Please let us know so we can fix it ASAP.")

    })
public Response upload(@Parameter(hidden = true) MultipartFormDataInputImpl form) {
    return null;
}


// used solely in request body @Schema implementation
class MultiRequest {
    @Schema(type = "string", format = "binary", description = "image file")
    public String file;
    @Schema(description = "image metadata")
    public MetadataRequest metadata;
}

this would resolve into:

paths:
  /test:
    post:
      summary: Upload a new image and associated metadata
      description: Long form description saying whatever we want
      operationId: upload
      requestBody:
        content:
          multipart/form-data:
            schema:
              $ref: '#/components/schemas/MultiRequest'
            encoding:
              file:
                contentType: application/pdf, image/png
      responses:
        200:
          description: The UUID of the newly uploaded image
        403:
          description: The provided credentials are insufficient to see this resource.
        415:
          description: The provided file type is not supported
        500:
          description: We messed up. Please let us know so we can fix it ASAP.
components:
  schemas:
    MultiRequest:
      type: object
      properties:
        file:
          type: string
          description: image file
          format: binary
        metadata:
          $ref: '#/components/schemas/RequestMetadata'
    RequestMetadata:
      type: object
      properties:
        foo:
          type: string
      description: image metadata