[BUG] [Go] generator for array typed schema component with --generate-alias-as-model flag creates uncompilable model

Description

Hi,
There is an issue in the modules/openapi-generator/src/main/resources/go/model_simple.mustache template, introduced in commit 4487042.

The ToMap function is not handling properly the case when the model isArray

func (o {{classname}}) ToMap() (map[string]interface{}, error) {
	toSerialize := {{#isArray}}make([]interface{}, len(o.Items)){{/isArray}}{{^isArray}}map[string]interface{}{}{{/isArray}}
...
	return toSerialize
}

here the ToMap function is returning a map[string]interface{} but the toSerialize will be a []interface{} in case the model is array.

Previously this was part of the MarshalJSON function, now this new MappedNullable interface is introduced for some reason, so the ToMap function was created but the original business logic template left there.

openapi-generator version

tested with openapitools/openapi-generator-cli:6.3.0
with openapitools/openapi-generator-cli:6.2.1 this issue does not occure.

OpenAPI declaration file content or url

openapi: 3.0.1
info:
  description: test
  title: test
  version: 1.0.0
paths: {}
components:
  schemas:
    A:
      items:
        properties:
          B:
            type: integer
        type: object
      type: array

Generation Details

openapi-generator-cli generate --generate-alias-as-model -i A.yaml -g go -o .

Steps to reproduce

Generate Go model with --generate-alias-as-model flag from the provided schema.

Related issues/PRs

Suggest a fix

I did not dig too deep why the MappedNullable interface had been introduced, but I can think of 3 solutions:

• Introduce a ArrayedNullable interface with []interface{} return type and use that in case the component is array typed
• Change the ToMap function's return value to interface{} or any in the MappedNullable and olso in the generated ToMap
• Revert back to the original MarshalJson implementation without the ToMap function call.

Start by reading modules/openapi-generator/src/main/resources/go/model_simple.mustache, then run the provided openapi-generator-cli command with the YAML schema and --generate-alias-as-model. Check the generated array model's ToMap return type and compile the generated Go model. Done means array-typed schema components generate compilable Go code.