Ref resolver doesn't follow JSON Reference specification

Using io.swagger.codegen.v3:swagger-codegen:3.0.7 it fails to resolve $ref aka JSON Reference. Calling new OpenAPIV3Parser().read("src/openapi/openapi.yaml") fails with:

java.lang.RuntimeException: Unable to load RELATIVE ref: ./schemas/index.yaml path: <path>/src/openapi

The API is not a Hello World so it is split to >30 files. Directory structure snippet:

openapi
├── components
│   ├── index.yaml
│   ├── parameters
│   │   └── index.yaml
│   ├── responses
│   │   └── index.yaml
│   └── schemas
│       ├── connection.yaml
│       ├── connectiondirection.yaml
│       ├── connectors
│       │   ├── connector.yaml
│       │    ...
│       │   └── impl
│       │       ├── foo.yaml
│       │        ...
│       │       └── bar.yaml
│       ├── index.yaml
│       ├── info.yaml
│        ...
│       ├── reports.yaml
│       ├── transaction.yaml
│       └── workflow.yaml
└── openapi.yaml

The issue is caused by a "nested" relative referencing:

/openapi.yaml
    $ref: "./components/index.yaml#foo"
/components/index.yaml
    foo:
       $ref: "./schemas/index.yaml#bar"
/components/schemas/index.yaml
    bar:
       ...

According to JSON Reference:

Resolution is performed relative to the referring document.

This means the ./schemas/index.yaml reference inside /components/index.yaml file shouldn't be resolved against the root directory but /components directory! On a first sight the io.swagger.v3.parser.ResolverCache.loadRef() operates with a static parentDirectory only.

This is a well-documented feature and different parsers work just fine.

Start with io.swagger.v3.parser.ResolverCache.loadRef(), then trace how OpenAPIV3Parser.read("src/openapi/openapi.yaml") resolves the nested references in the issue. Reproduce the supplied openapi.yaml, components/index.yaml, and components/schemas/index.yaml structure, and verify that each relative reference is resolved against its referring document rather than the root directory.