[BUG][GO] Incorrect field name (syntax error) in generated code with `oneOf` and empty object.

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

We would like a field to map to either (= oneOf) a defined object or an empty type: object subschema so that the generated code does not json-decode the field depending on circumstances.

In this case, the openapi-generator currently will generate code with compilation (syntax) errors similar to what's described in the related issue:

// FooPostRequestBaz - struct for FooPostRequestBaz
type FooPostRequestBaz struct {
	FooPostRequestBazOneOf *FooPostRequestBazOneOf
	MapmapOfStringinterface{} *map[string]interface{}

where MapmapOfStringinterface{} is not a valid field name.

Note 1: if the empty oneOf subschema is defined without a type (= undefined), the generated code will look like this:

// FooPostRequestBaz - struct for FooPostRequestBaz
type FooPostRequestBaz struct {
	FooPostRequestBazOneOf *FooPostRequestBazOneOf
	Interface{} *interface{}
}

where Interface{} is not a valid field name and *interface{} is not desired (should be interface{} instead).

Note 2: without the oneOf the generated request body is correct.

openapi-generator version

openapitools/openapi-generator-cli:latest sha256:aa8b02c8cdaef08f9478d967a5ea2640e94e6d63f34892ec72ef9458cf7ed305

OpenAPI declaration file content or url

https://gist.github.com/cooltea713705/6d94ac40546bc4ddef1ac34f7034e3c8

Generation Details

generatorName: go
generateInterfaces: true
validateSpec: false

Steps to reproduce

1. Generate client

Related issues/PRs

• https://github.com/OpenAPITools/openapi-generator/issues/16715

Suggest a fix

N/A

Start with the linked OpenAPI declaration and reproduce the issue using the Go generator with the reported settings. Inspect the generated request model and the generator path handling oneOf schemas with empty or undefined object subschemas; done means the generated Go code has valid field names, compiles, and represents the empty case as intended.