Invalid URL (jsonschema RefResolutionError)

Start at jsonschema.validators.resolve_from_url and trace how openapi-core invokes jsonschema for the YAML $ref './paths.yaml'. Confirm how relative references are resolved against the current directory, then verify that the example paths.yaml reference resolves without RefResolutionError.

We probably should install an extra handler for jsonschema, one that prepends file:// and resolves the current directory to all relative file name references. The relevant code that errors out:

    # jsonschema.validators
    def resolve_from_url(self, url):
        url, fragment = urldefrag(url)
        try:
            document = self.store[url]
        except KeyError:
            try:
                document = self.resolve_remote(url)
            except Exception as exc:
                raise RefResolutionError(exc)

        return self.resolve_fragment(document, fragment)

The code in question:

openapi: 3.0.1
servers:
  - url: 'https://example.com/api/v2.0/'
info:
  title: Example API
  description: Our awesome example API
  version: 1.1.0
tags:
  - name: Service
paths:
  $ref: './paths.yaml'

I have also tried file://./paths.yaml, which then results in it looking for /paths.yaml, which is an error of the file resolver jsonschema is using. Either way, we currently cannot resolve any relative file references, which are allowed and correctly working in other tools, including openapi-spec-validator. The latter is a bit odd, since it should be resolving references and validating them.