inverseRules:
  # Allow use of this package in all k8s.io packages.
  - selectorRegexp: k8s[.]io
    allowedPrefixes:

inverseRules:
  # Allow use of this package in all k8s.io packages.
  - selectorRegexp: k8s[.]io
    allowedPrefixes:

made, the import will be flagged as an error.

### What are rules files?

A rules file is a JSON or YAML document with two top-level keys, both optional:
* `Rules`
* `InverseRules`

### What are Rules?

A `rule` defines a policy to be enforced on packages which are depended on by
the package in question.  It consists of three parts:

inverseRules:
  - selectorRegexp: k8s[.]io
    forbiddenPrefixes:

inverseRules:
  - selectorRegexp: k8s[.]io
    allowedPrefixes:
      - k8s.io/kubernetes/cmd/import-boss/testdata/transitive/aaa

inverseRules:
  - selectorRegexp: k8s[.]io
    allowedPrefixes:

inverseRules:
  - selectorRegexp: k8s[.]io
    forbiddenPrefixes:
      - k8s.io/kubernetes/cmd/import-boss/testdata/transitive/aaa

inverseRules:
  # Allow Internal packages only in apiextensions-apiserver itself, discourage use elsewhere.
  - selectorRegexp: k8s[.]io/apiextensions-apiserver
    allowedPrefixes:
      - ''
  # Allow use from within e2e tests.
  - selectorRegexp: k8s[.]io/kubernetes/test
    allowedPrefixes:
      - k8s.io/kubernetes/test/e2e/apimachinery
  # Forbid use of this package in other k8s.io packages.
  - selectorRegexp: k8s[.]io
    forbiddenPrefixes:

		return filepath.Dir(pkg.GoFiles[0])
	}
	if len(pkg.IgnoredFiles) > 0 {
		return filepath.Dir(pkg.IgnoredFiles[0])
	}
	return ""
}

type FileFormat struct {
	Rules        []Rule
	InverseRules []Rule

	path string
}

// A single import restriction rule.
type Rule struct {
	// All import paths that match this regexp...
	SelectorRegexp string
	// ... must have one of these prefixes ...