func SplitMaybeSubscriptedPath(fieldPath string) (string, string, bool) {
	if !strings.HasSuffix(fieldPath, "']") {
		return fieldPath, "", false
	}
	s := strings.TrimSuffix(fieldPath, "']")
	parts := strings.SplitN(s, "['", 2)
	if len(parts) < 2 {
		return fieldPath, "", false
	}
	if len(parts[0]) == 0 {
		return fieldPath, "", false
	}
	return parts[0], parts[1], true
}
SplitMaybeSubscriptedPath checks whether the specified fieldPath is
subscripted, and
- if yes, this function splits the fieldPath into path and subscript, and
returns (path, subscript, true).
- if no, this function returns (fieldPath, "", false).

Example inputs and outputs:
- "metadata.annotations['myKey']" --> ("metadata.annotations", "myKey", true)
- "metadata.annotations['a[b]c']" --> ("metadata.annotations", "a[b]c", true)
- "metadata.labels['']"           --> ("metadata.labels", "", true)
- "metadata.labels"               --> ("metadata.labels", "", false)
package fieldpath
import (
	"fmt"
	"strings"
	"k8s.io/apimachinery/pkg/api/meta"
	"k8s.io/apimachinery/pkg/util/validation"
)
func FormatMap(m map[string]string) (fmtStr string) {
	for key, value := range m {
		fmtStr += fmt.Sprintf("%v=%q\n", key, value)
	}
	fmtStr = strings.TrimSuffix(fmtStr, "\n")
	return
}
func ExtractFieldPathAsString(obj interface{}, fieldPath string) (string, error) {
	accessor, err := meta.Accessor(obj)
	if err != nil {
		return "", nil
	}
	if path, subscript, ok := SplitMaybeSubscriptedPath(fieldPath); ok {
		switch path {
		case "metadata.annotations":
			if errs := validation.IsQualifiedName(strings.ToLower(subscript)); len(errs) != 0 {
				return "", fmt.Errorf("invalid key subscript in %s: %s", fieldPath, strings.Join(errs, ";"))
			}
			return accessor.GetAnnotations()[subscript], nil
		case "metadata.labels":
			if errs := validation.IsQualifiedName(subscript); len(errs) != 0 {
				return "", fmt.Errorf("invalid key subscript in %s: %s", fieldPath, strings.Join(errs, ";"))
			}
			return accessor.GetLabels()[subscript], nil
		default:
			return "", fmt.Errorf("fieldPath %q does not support subscript", fieldPath)
		}
	}
	switch fieldPath {
	case "metadata.annotations":
		return FormatMap(accessor.GetAnnotations()), nil
	case "metadata.labels":
		return FormatMap(accessor.GetLabels()), nil
	case "metadata.name":
		return accessor.GetName(), nil
	case "metadata.namespace":
		return accessor.GetNamespace(), nil
	case "metadata.uid":
		return string(accessor.GetUID()), nil
	}
	return "", fmt.Errorf("unsupported fieldPath: %v", fieldPath)
}