[BUG][GO] JSON marshalling incorrect when setting anyOf properties as required

[perhallgren]

Bug Report Checklist

• [x] Have you provided a full/minimal spec to reproduce the issue?
• [x] Have you validated the input using an OpenAPI validator (example)?
• [x] Have you tested with the latest master to confirm the issue still exists?
• [x] Have you searched for related issues/PRs?
• [x] What's the actual output vs expected output? Expecting marshalling to produce

  {"obj":"A"} 

  But it produces

  {"obj":{"Int32":null,"String":"A"}}

• [ ] [Optional] Sponsorship to speed up the bug fix or feature request (example)

Description

When an anyOf model is a required property, JSON marshalling is incorrect.

openapi-generator version

docker run --rm openapitools/openapi-generator-cli:latest version
7.10.0-SNAPSHOT

OpenAPI declaration file content or url

openapi: 3.0.0
info:
  version: 1.0.0
  title: FooBar Service
paths: {}
components:
  schemas:
    Bad:
      type: object
      description: bad
      required:
        - obj
      properties:
        obj:
          $ref: '#/components/schemas/Obj'
    Obj:
      anyOf:
        - type: string
        - type: integer
      example: a
      description: obj

Generation Details

I'm running

docker run --rm -v "${PWD}:/local" openapitools/openapi-generator-cli:latest generate \
        --input-spec /local/go-json-marshal.yaml \
        --generator-name go \
        --additional-properties "withGoMod=false" \
        --package-name gen \
        --output /local/gen

Steps to reproduce

Run this gist

Related issues/PRs

• https://github.com/OpenAPITools/openapi-generator/pull/19962
• https://github.com/OpenAPITools/openapi-generator/issues/14028

Suggest a fix

• https://github.com/OpenAPITools/openapi-generator/pull/19962

[perhallgren]

Looks like the same issue: https://github.com/OpenAPITools/openapi-generator/issues/14028