[BUG][Go] Panic when error is JSON array

[thiagoarrais]

Description

It seems like since #13680 openapi-generator's Go template assumes that JSON responses are single objects. But when ran against APIs that returns object arrays, it panics when trying to parse error messages. I've chased this down to the use of formatErrorMessage as demonstraded on Go Playground FQ8Js4GaBuv.

openapi-generator version

6.2.1 onwards. Reproduced against 6.5.0, which is latest stable as of this writing. 6.2.0 presents no problem.

OpenAPI declaration file content or url

openapi: 3.0.0
info:
  title: OpenAPI Library Demo App
  version: 0.0.1
servers: [
  {
    "url": "http://localhost:8000",
    "description": "local development server",
  },
]
paths:
  /books:
    get:
      responses:
        "422":
          description: error
          content:
            application/json:
              schema:
                type: array
                items:
                  type: object
                  properties:
                    message:
                      type: string

Suggest a fix

Maybe ensuring that metaValue' is a struct (by virtue of it's Kind field) before calling FieldByName will do the trick. See the docs for FieldByName.

[gcatanese]

@thiagoarrais Good catch, I have created #15154 to address it. Thank you!