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

In version 6.0.0, if oneOf is used in the schema for a query parameter, the generated code is wrong in a few ways:

• The file which contains the type definition for the parameter also has code referencing functions that do not exist:
  
• The interface generated for the query parameters uses the type from that file but doesn't import it:
  

openapi-generator version

6.0.0. This is a regression from version 5.4.0.

OpenAPI declaration file content or url

https://gist.github.com/targos/ce0dcf58be520f94c1bdab868f14e17b

Generation Details

{
  "$schema": "node_modules/@openapitools/openapi-generator-cli/config.schema.json",
  "spaces": 2,
  "generator-cli": {
    "version": "6.0.0",
    "generators": {
      "typescript-fetch": {
        "generatorName": "typescript-fetch",
        "glob": "openapi.json",
        "output": "test/api",
        "additionalProperties": {
          "enumPropertyNaming": "UPPERCASE"
        }
      }
    }
  }
}

Steps to reproduce

npm install -D @openapitools/openapi-generator-cli
npx openapi-generator-cli generate

Related issues/PRs

Suggest a fix