Openapi-generator: [BUG][Go][Client] Empty object generates compilation failure

[qmuntal]

Version
4.1.1

Command line used for generation
openapi-generator generate -i swagger.yaml -g go-o ./

Spec

swagger: "2.0"
info: 
  title: Foo
  version: v1
paths: 
  /foo: 
    post:
      operationId: fooPost
      parameters: 
        - 
          in: body
          name: body
          required: false
          schema: 
            $ref: "#/definitions/Foo"
      responses: 
        200: 
          description: "successful operation"
definitions: 
  Foo: 
    type: object

Description
Generated Foo model is:

type FooPostOpts struct {
    Body optional.Map[string]interface{}
}

which does not compile as optional.Map does not exist.
I would expect this model definition instead:

type FooPostOpts struct {
    Body map[string]interface{}
}

I can reproduce this issue with any object without properties.

cc @antihax (2017/11) @bvwells (2017/12) @grokify (2018/07) @kemokemo (2018/09) @bkabrda (2019/07)
@wing328

[qmuntal]

It seems that an empty object is tagged as isBinary=false. This cause that the generation automatically capitalize the first letter of the type and adds the optional. prefix to id, hopping that antihax/optional has that type implemented, which in this case it does not.

@antihax I´m not sure if map[interface]string could be implemented in your package, or even if it makes sense. WHat do you think?

Another solution could be to handle this type as a special case, as we already do in AbstractGoCodegen.java#L405 and map it to optional.Interface or tag it as isBinary=true.

[wing328]

Looks like the mapping is correct:

https://github.com/OpenAPITools/openapi-generator/blob/master/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/AbstractGoCodegen.java#L110

but the reference (alias) is not resolved correctly somehow.

There's another PR trying to map "object" to just interface: https://github.com/OpenAPITools/openapi-generator/pull/3878

Please review that PR when you've time.

[olegsu]

Any update on the PR guys?