[BUG] [C] Enum is attempted to be freed

[bookerdj]

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 certain cases when providing an enum as an input the generated C code will attempt to free the enum after it is used.
For the example spec provided it generates this enum:

// Enum CASCADES for ControllerAPI_deleteitem
typedef enum  { simple_api_deleteitem_CASCADES_NULL = 0, simple_api_deleteitem_CASCADES_none, simple_api_deleteitem_CASCADES_subitem } simple_api_deleteitem_cascades_e;

Which is used once

    simple_api_deleteitem_cascades_e valueQuery_cascades ;
    keyValuePair_t *keyPairQuery_cascades = 0;
    if (cascades)
    {
        keyQuery_cascades = strdup("cascades");
        valueQuery_cascades = (cascades);
        keyPairQuery_cascades = keyValuePair_create(keyQuery_cascades, (void *)strdup(deleteitem_CASCADES_ToString(
		valueQuery_cascades)));
        list_addElement(localVarQueryParameters,keyPairQuery_cascades);
    }

And then for some reason freed which causes a compilation error:

    if(valueQuery_cascades){
        free(valueQuery_cascades);
        valueQuery_cascades = NULL;
    }

openapi-generator version

Originally seen with 6.2.1 and reproduced on 6.5.0 and latest 6.60 snapshot

OpenAPI declaration file content or url

openapi: 3.0.1
info:
  title: Simple API
  version: 1.0.0
servers:
- url: /
paths:
  /{id}:
    delete:
      tags:
      - controller
      summary: Deletes an item and optionally its subitems
      description: |-
        Deletes an item

        Minimum API version: 1.0
      operationId: deleteitem
      parameters:
      - name: id
        in: path
        description: |-
          Delete the specific item in the form of xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx
          Minimum API version: 1.0
        required: true
        schema:
          type: string
      - name: cascades
        in: query
        schema:
          type: string
          enum:
            - none
            - subitem
      responses:
        204:
          description: Deleted the item and any associated subitems
          content: {}

Generation Details

java -jar ../openapi-generator-cli-6.6.0-20230420.080546-29.jar generate -g c  --additional-properties=prependFormOrBodyParameters=true -o out -i ../simple.yaml

Steps to reproduce

1. Generate the C client with the above command line and the provided spec
2. Observe the incorrect code output in out/api/ControllerAPI.c

Related issues/PRs

I tried out this PR which mentions fixing C enums but it didn't fix the issue #14434

Suggest a fix

The only extra information I have is that the issue goes away if I define a schema in the response such as the following:

openapi: 3.0.1
info:
  title: Simple API
  version: 1.0.0
servers:
- url: /
paths:
  /{id}:
    delete:
      tags:
      - controller
      summary: Deletes an item and optionally its subitems
      description: |-
        Deletes an item

        Minimum API version: 1.0
      operationId: deleteitem
      parameters:
      - name: id
        in: path
        description: |-
          Delete the specific item in the form of xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx
          Minimum API version: 1.0
        required: true
        schema:
          type: string
      - name: cascades
        in: query
        schema:
          type: string
          enum:
            - none
            - subitem
      responses:
        204:
          description: Deleted the item and any associated subitems
          content:
            application/json:
              schema:
                type: object