[BUG][Golang][Client] Response JSON array of object not handled in spec 2.0 but works in spec 3.0

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• What's the version of OpenAPI Generator used?
• Have you search for related issues/PRs?
• What's the actual output vs expected output?
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Description

When using an OAS 2.0 spec with a response that is an array of object, the generated code attempts to return a map[string]interface{} which runs into an error when the array is unmarshaled.

OAS 2.0 results in the following method signature which attempts to return a map[string]interface{}

func (a *LocalesApiService) GetAllLocales(ctx context.Context) (map[string]interface{}, *http.Response, error) {

This results in the following error:

json: cannot unmarshal array into Go value of type map[string]interface {}

Using an OAS 3.0 spec works as expected. It returns a []Locale as expected:

func (a *LocalesApiService) GetAllLocales(ctx context.Context) ([]Locale, *http.Response, error) {

openapi-generator version

4.1.0-SNAPSHOT, master branch

OpenAPI declaration file content or url

Non-working 2.0 spec: https://github.com/grokify/go-ringcentral-engage/blob/fd5a68df4d1612de69bed7e35c10ceb337a8da32/codegen/partial-specs_v2.0.0/openapi-spec_locales.json

Working 3.0 spec: https://github.com/grokify/go-ringcentral-engage/blob/fd5a68df4d1612de69bed7e35c10ceb337a8da32/codegen/partial-specs_v3.0.0/openapi-spec_locales.json

Command line used for generation

$ java -jar openapi-generator-cli.jar generate -i partial-specs_v3.0.0/openapi-spec_locales.json -g go -o engagedigital --package-name engagedigital

Steps to reproduce

Build a SDK against the linked specs.

Related issues/PRs

https://github.com/grokify/go-ringcentral-engage/issues/2

Suggest a fix

Make it work like the OAS 3.0 spec.

Start by generating the Go client from the linked OAS 2.0 and OAS 3.0 locale specs using the provided command, then compare the GetAllLocales signatures and response unmarshalling. The fix is done when the OAS 2.0 response generates and unmarshals as []Locale rather than map[string]interface{}.