[BUG][typescript-axios] Description

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 multipart/form-data responseBody primitive enums are treated as complex objects and serialized as a JSON Blob instead of plaintext.

Generated output

localVarFormParams.append('type', new Blob([JSON.stringify(type)], { type: "application/json", }));

Expected output

localVarFormParams.append('type', type as any);

openapi-generator version

Current version 5.3.0

This is a regression that was introduced in 5.0.0-beta3 but worked in 5.0.0-beta2. I think it was introduced by #7816.

OpenAPI declaration file content or url

openapi: "3.0.0"
info:
  version: 1.0.0
  title: Swagger Petstore
  description: Multi-file boilerplate for OpenAPI Specification.
  license:
    name: MIT
  contact:
    name: API Support
    url: http://www.example.com/support
    email: support@example.com
servers:
  - url: http://petstore.swagger.io/v1
tags:
  - name: pets
paths:
  /pet/upload:
    post:
      summary: Upload pet
      operationId: uploadPet
      description: Upload your pet
      tags:
        - pets
      requestBody:
        content:
          multipart/form-data:
            schema:
              type: object
              required:
                - type
                - file
              properties:
                type:
                  $ref: "#/components/schemas/PetType"
                file:
                  type: string
                  format: binary
      responses:
        201:
          description: OK
components:
  schemas:
    PetType:
      type: string
      enum:
        - Dog
        - Cat

Steps to reproduce

https://replit.com/@dantman/OpenAPI-generator-typescript-axios-multipart-enum

Suggest a fix

The issue seems to be that {{^isPrimitiveType}} is used for enum types (i.e. enums are considered a complex types like type: object instead of a primitive type like the type: string they are based on.

Fixing whatever code handles isPrimitiveType to consider enums primitive could be a way to fix this.

Start with the typescript-axios generator and the isPrimitiveType handling used for multipart/form-data responses. Reproduce the supplied OpenAPI declaration or linked Replit example, then inspect the generated append call for the enum. Done means primitive enum values are emitted as plaintext rather than JSON Blobs, with the generated output matching the expected form.