[BUG][C++][Pistache] Array of enumerated strings generates code that won't compile

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

Forgive me, this is my first Github issue ever.

I noticed that when using an array of enumerated strings, the generated code fails to compile.

The below example will dictate why.

        operatingMode:
          type: array
          items:
            type: string
            enum: ['A', 'B','C','D','E','F']

The below line success = value.validate(msg, currentValuePath) && success; added will fail to compile as vector obviously has no validate method.

    if (operatingModeIsSet())
    {
        const std::vector<std::string>& value = m_OperatingMode;
        const std::string currentValuePath = _pathPrefix + ".operatingMode";
                
        #pragma region MY_COMMENTS
        // This line is generated erroneously, and causes compilation problems
        #pragma endregion MY_COMMENTS

        success = value.validate(msg, currentValuePath) && success;

        #pragma region MY_COMMENTS
        // Correctly identifies this member as an array/vector
        #pragma endregion MY_COMMENTS

        { // Recursive validation of array elements
            const std::string oldValuePath = currentValuePath;
            int i = 0;
            for (const std::string& value : value)
            { 
                const std::string currentValuePath = oldValuePath + "[" + std::to_string(i) + "]";
                        
        //...

I believe this issue lay here in the file model-validation-body.mustache

        {{^isString}}{{#allowableValues.enumVars.0.value}}

        success = value.validate(msg, currentValuePath) && success;

My current workaround is doing the following, but I believe this is ultimately not the cleanest and my mustache skills leave much to be desired.

        {{^isString}}{{#allowableValues.enumVars.0.value}}
        {{^isArray}}
        success = value.validate(msg, currentValuePath) && success;
        {{/isArray}}

openapi-generator version

• openapi-generator-cli-5.2.1.jar

Though I believe this to be a problem in master in general.

OpenAPI declaration file content or url

openapi: 3.0.0
servers:
  - url: 'http://localhost:8080/v2'
info:
  description: >-
    This is a sample rest server. For this sample, you can use the api key
    `special-key` to test the authorization filters.
  version: 1.0.0
  title: OpenAPI
  license:
    name: Apache-2.0
    url: 'https://www.apache.org/licenses/LICENSE-2.0.html'
tags:
  - name: test
    description: Functions related to test interactions
paths:
  /test/status:
    post:
      tags:
        - test
      summary: Sends a test status message
      description: 'sends test data'
      operationId: sendtestStatus
      responses:
        '200':
          description: successful operation
        '405':
          description: Invalid input
      requestBody:
        $ref: '#/components/requestBodies/testStatus'
externalDocs:
  description: Find out more about Swagger
  url: 'http://swagger.io'
components:
  requestBodies:
    testStatus:
      content:
        application/json:
          schema:
            $ref: '#/components/schemas/testStatus'
            x-body-name: test_status
      description: testStatus object that needs to be added
      required: true
  securitySchemes:
    api_key:
      type: apiKey
      name: api_key
      in: header
  schemas:
    testStatus:
      title: testStatus
      description: A tests status
      type: object
      properties:
        operatingState:
          type: string
          enum: ['1', '2','3','4','5','6']
        operatingMode:
          type: array
          items:
            type: string
            enum: ['A', 'B','C','D','E','F']
      xml:
        name: testStatus

Generation Details

My Dockerfile with some information redacted.

ARG OPENAPI_GENERATOR_VERSION=5.2.1
ARG OPENAPI_SCHEMA=api.yml
ARG OPENAPI_IMPL=cpp-pistache-server
ARG EXTRA_ARGS_TO_GENERATOR=

FROM ${REPO}ubuntu:18.04 as generator

RUN apt-get update && apt-get install -y wget default-jre && rm -rf /var/lib/apt/lists/

ARG ARTIFACTORY_MAVEN_REPO
ARG OPENAPI_GENERATOR_VERSION
ARG OPENAPI_SCHEMA
ARG EXTRA_ARGS_TO_GENERATOR
ARG OPENAPI_IMPL

RUN wget "${ARTIFACTORY_MAVEN_REPO}/org/openapitools/openapi-generator-cli/${OPENAPI_GENERATOR_VERSION}/openapi-generator-cli-${OPENAPI_GENERATOR_VERSION}.jar" -O openapi-generator-cli.jar

COPY mustache/* /openapi/codegen/templates/
COPY ${OPENAPI_SCHEMA} /openapi/

RUN mkdir src-gen && java -jar openapi-generator-cli.jar generate -i /openapi/${OPENAPI_SCHEMA} -g ${OPENAPI_IMPL} -o src-gen/ -t /openapi/codegen/templates ${EXTRA_ARGS_TO_GENERATOR}

Steps to reproduce

• Generate source from provided api using command java -jar openapi-generator-cli.jar generate -i /openapi/api.yml -g cpp-pistache-server -o src-gen/
• Try to compile, fail due to this issue
• Add this fix to CMakeLists.txt

ExternalProject_Add(PISTACHE
    # TRACK THIS BUG REPORT https://github.com/OpenAPITools/openapi-generator/issues/9148
    GIT_TAG 0d09ab982edd03bc8457fa6351af7d0c4a135da2

• See compilation failure

Related issues/PRs

• []

Suggest a fix

Maybe this as referenced above?

        {{^isArray}}
        success = value.validate(msg, currentValuePath) && success;
        {{/isArray}}

Start with modules/openapi-generator/src/main/resources/cpp-pistache-server/model-validation-body.mustache and the provided OpenAPI schema, then reproduce with the documented generate command. Check the generated C++ for an array of enum strings and confirm compilation succeeds while scalar enum validation remains intact.