Improve plugin home defaulting.

api/types/errunabletofind.go

@@ -0,0 +1,40 @@
+// Copyright 2019 The Kubernetes Authors.
+// SPDX-License-Identifier: Apache-2.0
+
+package types
+
+import (
+	"fmt"
+	"strings"
+
+	"github.com/pkg/errors"
+)
+
+type errUnableToFind struct {
+	// What are we unable to find?
+	what string
+	// What things did we try?
+	attempts []Pair
+}
+
+func (e *errUnableToFind) Error() string {
+	var m []string
+	for _, p := range e.attempts {
+		m = append(m, "('"+p.Value+"'; "+p.Key+")")
+	}
+	return fmt.Sprintf(
+		"unable to find plugin root - tried: %s", strings.Join(m, ", "))
+}
+
+func NewErrUnableToFind(w string, a []Pair) *errUnableToFind {
+	return &errUnableToFind{what: w, attempts: a}
+}
+
+func IsErrUnableToFind(err error) bool {
+	_, ok := err.(*errUnableToFind)
+	if ok {
+		return true
+	}
+	_, ok = errors.Cause(err).(*errUnableToFind)
+	return ok
+}